NASA SP-493

ReflectanceSpectroscopy

inPlanetary

Science

Review and Strategyfor the Future

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https://ntrs.nasa.gov/search.jsp?R=19880015180 2018-05-29T05:36:29+00:00Z

NASA SP-493

ReflectanceSpectroscopy

inPlanetary

Science

Review and Strategyfor the Future

Thomas B. McCord, editor

f\|/\C%/\ Scientific an£l Technical Information Division 1988National Aeronautics and Space Administration

Washington, DC

Workshop Participants

Thomas B. McCord, Hawaii Institute of Geophysics, University of Hawaii - Chairman and editorJohn B. Adams, Department of Geology, University of Washington - Chapter 7 leaderJeffrey F. Bell, Hawaii Institute of Geophysics, University of HawaiiRobert H. Brown, Space Sciences Division, Jet Propulsion LaboratoryRoger G. Burns, Department of Earth and Planetary Sciences, Massachusetts Institute of TechnologyMichael Carr, U.S. Geological SurveyRoger N. Clark, Remote Sensing Section, U.S. Geological SurveyMichael J. Gaffey, Department of Geology, Rensselaer Polytechnic Institute - Chapter 2 and 3

contributorBruce W. Hapke, Department of Geology and Planetary Sciences, University of PittsburghB. Ray Hawke, Hawaii Institute of Geophysics, University of HawaiiRobert E. Johnson, Department of Nuclear Energy and Energy Physics, University of VirginiaTbrrence V. Johnson, Space Sciences Division, Jet Propulsion Laboratory - Chapter 6 leaderDouglas B. Nash, Space Sciences Division, Jet Propulsion Laboratory - Chapter 4 leaderRobert M. Nelson, Space Sciences Division, Jet Propulsion LaboratoryCarle M. Pieters, Department of Geology, Brown University - Chapter 5 leaderJames B. Pollack, Space Sciences Division, NASA Ames Research CenterDavid H. Scott, Solar System Exploration Division, NASA - SponsorGodfrey T. Sill, Lunar and Planetary Laboratory, University of ArizonaWilliam D. Smythe, Space Sciences Division, Jet Propulsion LaboratoryZeny Cocson, Hawaii Institute of Geophysics, University of Hawaii - Secretary

Other Contributors

Raymond E. ArvidsonEraser P. FanaleJonathan C. GradieLucy-Ann A. McFaddenRichard V. MorrisRobert B. Singer

Library of Congress Cataloging-in-Publication Data

Reflectance spectroscopy in planetary science.

(NASA SP ; 493)1. Imaging systems in astronomy-Congresses.

2. Reflectance spectroscopy-Congresses. 3. Astronomicalspectroscopy-Congresses. I. McCord, Thomas B.II. Series.QBS1.3.E43R44 1988 522'.67 87-28154

For sale by the Superintendent of Documents, U.S.Government Printing Office, Washington, DC 20402

Preface

Reflectance spectroscopy is one of several remotesensing techniques used to study the surfaces andatmospheres of solar system objects. It has become oneof the most important techniques because it providesfirst-order information on the presence and amountsof certain ions, molecules, and minerals on a surfaceor in an atmosphere. This sort of information is criticalto (1) develop models of the chemical andthermodynamic history of the interior of a solid bodyby determining the present exposures of primarymaterials or their weathering products; (2) determinethe processes altering the material by studying theweathering products; and (3) determine the spatialdistribution of rock types and minerals on the surfaceand make better geologic maps. The technique can becontrasted with and is complementary to the techniqueof monochromatic imaging, which is used to determinethe morphology of a surface, using landforms asindicators of processes which formed and altered theobject.

In light of the extensive planned use of reflectancespectroscopy on most current and future solar systemexploration spacecraft missions and the resulting heavydemands which will be placed on the reflectancespectroscopy community, there is a need to assesscurrent capabilities, facilities, and personnel and thefocuses and directions of current efforts. Also, the fieldhas developed considerably over the past 15 years with-out a formal review by its members. Finally, in thecurrent climate of decreasing research budgets, it isimportant to review the field, state the recognizedimportant future directions and needs, and restate goalsand objectives.

A workshop was held and this report written underthe sponsorship of the NASA Office of Space Science

and Applications Planetary Geology and GeophysicsProgram. A major effort was made during the 3-dayworkshop held April 9-11, 1986, in Yountville, California.A wide spectrum of investigators active in the field wasinvited, and most attended. Many of those who couldnot attend contributed written material and reviews ofthe report drafts.

Written material generated at the workshop wasconsolidated by the chapter leaders and the workshopchairman within a few weeks after the workshop. Thechairman edited this material and his own notes intoa first draft of the report, which was circulated amongthe participants for extensive review. The results of thisreview were used by the chairman to prepare a sec-ond draft. In August this second draft was circulatedmore widely throughout the community, including theoffice of the NASA sponsor. The final report wasprepared in October 1986 by the chairman from theresponses to the second draft. Almost all therecommendations of the participants were included inthe report, reflecting the wide agreement within thecommunity.

This report is intended as a start rather than thecompletion of a review of the field. NASA's need ofinformation for programmatic reasons at this timedictated a hasty and therefore incomplete response. Oneof the major recommendations is that a furtherassessment and a revision of this document be madewithin 2 years.

The near-complete participation and the high level ofenthusiasm exhibited by the community for thisendeavor are strong indicators of the vigor and healthof the field. Members of the community are inagreement on many of the issues and are anxious towork together to explore the solar system.

111

Acknowledgment

The efforts of Zeny Cbcson and her staff are greatly appreciated.

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Contents

Preface iii

Acknowledgment iv

Chapter 1 Summary and Key Findings 1

Chapter 2 Purpose and Scope of the Workshop 7

Chapter 3 The Field of Reflectance Spectroscopy 9

Chapter 4 Contributions 13

Chapter 5 Current Capabilities and Resources 17

Chapter 6 Future Applications and Requirements 27

Chapter 7 Strategy and Implementation 35

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Chapter 1Summary and Key Findings

IOrigin and Purpose of this ReportThe field of reflectance spectroscopy as a remote

sensing tool applied to the study of solar system objectshas blossomed in the past 15 years, resulting in majordiscoveries about almost all solar system objects.Reflectance spectroscopy has become one ofthe most important investigations on mostcurrent and planned NASA Solar SystemExploration Program space missions. Thereflectance spectroscopy effort encompasses virtuallyall objects in the solar system, and it involves manydisciplines other than spectroscopy, such as geology,geochemistry, geophysics, and atmospheric sciences.This development has depended on and resulted inincreased activity in this area within the NASA basicresearch and data analysis program. Tight restrictionof funds for the program has created hardship withinthe field, and the growth of the field has affected otherdisciplines. Yet the new mission investigations requiremajor support from this field and NASA, and theresearch field must plan for this need. This report isthe product of a three-day workshop held in April 1986.

IKey FindingsReflectance spectroscopy has proven to be themost powerful technique for determiningsurface lithologic composition by remotesensing.

The U.S. solar system exploration program willplace even greater demands on the reflectancespectroscopy field than it has in the past.

There presently exists an appalling mismatchbetween the objectives of NASA (and foreign)planetary missions to conduct high data ratereflectance spectroscopy experiments and thepresent capabilites for data handling, analysis,and interpretation.

The existing reflectance spectroscopy efforthighly leveraged and vulnerable to changesoutside programs and institutions.

I

isin

Communications are not sufficient.creators of basic knowledge (e.g. surface

mineralogy)-«-"-users (e.g. volcanologists)

spacecraft projects/investigations--—«-basicresearch community

planetary program*—^terrestrial remotesensing program

research/projects -—-NASA Headquartersmanagement

Description of the FieldReflectance spectroscopy in the NASA Solar System

Exploration Program is the measurement andinterpretation of solar flux passively scattered from thesurfaces and atmospheres of solar system objects. Thewavelength range covers the near ultraviolet to the mid-infrared, approximately 0.2 /i to 5.0 p. The spectralfeatures sought are absorptions due to photon-inducedelectronic and molecular energy transitions within thesurface minerals and the atmospheric particles andgases. Mineral and gas species and their abundancescan often be identified from these spectral features.

The successful application of reflectancespectroscopy requires serious and interactiveeffort in each of several distinct and equallyimportant areas:

Development and maintenance of laboratory,telescopic, flight instrumentation, dataprocessing software and related personneland facilities

Measurement of planetary reflectancespectra using ground-based, Earth-orbital anddeep space probes

Laboratory measurement of spectra andrelated study of the properties of materials

Development of theory and models ofreflectance and scattering and interpretationtechniques and methods

Design of planetary investigations andinterpretation of the resulting data with focuson well-defined scientific problems

Reflectance spectroscopy has proven to bethe most powerful technique for determiningsurface lithologic and thick atmosphericcompositions by remote sensing. From Mercuryto Pluto, almost everything known about surfacemineralogy (except for Earth and the Moon, for whichwe have direct documented samples, and for indirectinferences from morphology) has resulted fromreflectance spectroscopy, using ground-based telescopes.A long list of scientific contributions is given in thisreport (chapter 3). These include mapping of hightitanium minerals on the lunar maria and discovery ofolivine-rich rock in some central peaks derived fromdepth, basalt rocks on Vesta, ice as the major constituenton most outer solar system satellites, sulfur as a majormineral involved in the volcanism on lo, iron oxide andclay minerals on Mars, and the fact that meteoriticmineral assemblages are similar to those composingmost asteriods. There is groundtruth confirmation ofenough of the remote measurements to lend credibilityto the technique. These include lunar samples returnedfrom areas measured remotely and meteoritic materialsfrom asteroids.

This report contains a summary of current capabilitiesfor deriving scientifically useful information for solarsystems studies using reflectance spectroscopytechniques (chapter 4). The basic measurementobjectives of the technique are:

Identify the presence of specific minerals andgases and map their distribution.Determine the abundance of mineralspresent. ••Estimate the composition of the individualminerals.

For minerals with strong, well-defined absorptionbands (e.g., pyroxene, olivine, water ice), it is possibleto detect their presence as only a few percent of thesurface material and to estimate their abundance andindividual key element compositions to 5 or 10%. Otherminerals with no absorption bands (e.g., carbon) canbe detected only by inference.

A summary of the facilities and personnel involvedin spectral reflectance work under the NASA programis provided in chapter 4. The three closely related dataacquisition and analysis activities are

Obtain reflectance data for planetary surfacesthrough a well-planned data acquisitionprogram (ground-based and Earth-orbitaltelescopes and deep space probes).Establish a solid foundation of laboratoryreflectance spectroscopy measurements formaterials and conditions appropriate for thesurfaces studied.Develop accurate theoretical and appliedanalysis capabilities to interpret the data andextract the desired information.

Reflectance spectroscopy is a technique, and it ismeasurement oriented. Measurement, however, is notan end itself but rather a means to answer a scientificquestion. It is extremely important that thedevelopment and application of reflectancespectroscopy as a technique be motivated bybasic scientific questions about the solarsystem and the objects and material concerningit. This is the case for almost all the investigators'programs, for review committees are extremely sensitiveto this issue and funding is so restricted. On the otherhand, no one investigator can be equally active andcompetent in all areas of investigation required for thedevelopment and application of a technique. Thus, thefield should be reviewed overall for its balanceof technique and science, and individualinvestigators should be allowed to emphasizeareas of specialty as long as there iscommunication among investigators and thefield as a whole is in balance. Consortia are a gooddevice for helping technique-oriented investigators focuson scientific problems and for keeping theoreticalscientists within the reality of the data and using thebest observational and modeling capabilities.

There are about 18 university, NASA center, and U.S.Geological Survey locations at which at least oneinvestigator is active in reflectance spectroscopy asapplied to planetary studies. About half these programshave only one investigator; the total number ofinvestigators is about 30. Most investigators do not spendfull time on planetary reflectance spectroscopy, andsome are not funded at all by the NASA program. Thereis very little overlap among investigators and institutionprograms. This indicates a rather thin spread ofresearch personnel with the associated risk of toolittle communication.

Essentially all the existing reflectance spectrafor planetary objects have been obtained usingground-based telescopes. No U.S. spacecraft hascarried a reflectance spectrometer to a planetary object.The IUE Earth-orbital telescope has been used forultraviolet observations of asteroids, comets, and Galileansatellites. The Space Telescope instrumentation will allowobservations in the ultraviolet and visible spectra.

Laboratory measurement and models ofreflectance properties of materials are essentialfor developing the methods, backgroundinformation, and the models to interpretplanetary data. Laboratory measurements shouldconcentrate on well-documented samples and on end-member materials and mixtures. Models should bedeveloped and used to extend the laboratorymeasurements to the general case of different mixtures,geometries, and other conditions to avoid massivemeasurement projects and to respond quickly to a newplanetary measurement. At least 13 research centershave laboratory reflectance spectroscopic measurement

I

capability, and at least 6 of these have only oneinvestigator active in this work. Yet there is very littleoverlap in the work at these centers, most centers haveonly limited capability, and some needed capabilities donot exist at all. Not only must the spectra be measured,but the conditions of a planetary environment, includingtemperature, pressure, and radiation, must often bereproduced.

Existing data sets for planetary objects andlaboratory materials are scattered and not welldocumented. This is typical of most remote sensingresearch fields. The Planetary Data System project isbeing implemented in an attempt to overcome thisproblem. The PDS should take into account theneeds of the reflectance spectroscopy field byestablishing at least one discipline node andseveral investigator nodes.

New spectrum and image cube data handlingand analysis software systems are particularlyimportant to handle the expected very largedata sets from the NIMS and VIMS spacecraftinstruments and the similar ground-basedtelecope instruments about to becomeoperational. Several image cube systems are underdevelopment (GARP, SPAM). GARP is almost entirelydirected at mission support, and SPAM is largely aneffort of the terrestrial remote sensing program. SPECPRis a one-dimensional spectrum processing system which,is fairly mature. At present, the capability tohandle imaging spectrometer data sets of thevolume expected does not exist.

Future Applications, andRequirements

The U.S. Solar System Exploration Program,as now planned , will place demands on thereflectance spectroscopy field far greater thanin the past. Imaging spectroscopy techniques willincreasingly dominate spectral reflectance studies. Inaddition to even more sophisticated and extensivetelescopic studies of planetary reflection spectra, majorspacecraft mission data sets with many orders ofmagnitude and more data volume for a variety of bodieswill be available in the next decade. The Galileo and MarsObserver mission payloads contain reflectancespectrometers as do the strawman payloads for theGRAF, LGO, and Cassini missions. It appears thatcompeting solar system exploration programs in othercountries will also include these investigations.

It is recommended that efforts be accelerated inseveral critical areas. Theoretical and laboratorystudies aimed at interpreting planetary spectrafrom diverse surfaces are needed. These shouldinvolve detailed measurements of well-characterizedminerals and condensed volatiles (including

I

environmentally controlled studies) appropriate forexploration of outer satellites, Mars, the Moon, cometsand asteroids. Investigation of alteration and weatheringprocesses and products (including the effects ofirradiation) for these bodies is also needed. Developmentof accurate theoretical and analytical capabilities isrequired to extract the essential compositionalinformation from complex spectra of the surfaces ofthese bodies. Earth-based telescopic observationsmust be continued; we must have information aboutthe spectra and geochemical properties of solar systemobjects in order to properly plan and carry outspacecraft missions and to provide the realistic data setsnecessary to develop and test analysis techniques.Techniques for handling imaging spectroscopicdata sets must be further developed so that therapid advances in instrumentation and spacecraftexperiments yield comparable advances in the ;understanding of the geochemistry and geology ofplanetary surfaces. Data sets should be catalogedand maintained in living data bases for betteraccess by the scientific community.

All this can and should be done while an emphasison scientific issues and questions is maintained (seechapter 6).

Strategy and ImplementationCertain aspects of the reflectance

spectroscopy program urgently requireattention if the mission and science objectivesdiscussed previously are to be met. These includecritical research problems and other problems that arelargely programmatic in nature. More detaileddiscussions of some of these problems and proposedsolutions appear in chapter 7.

Mission ReadinessSpectra have been treated on an individual basis, and

we have not had to be concerned with processing largequantities of data. Multispectral images have beensimilarly treated on an individual basis or for only a fewbands. However, future missions (and telescopicinvestigations) will produce an unprecedented flood ofspectroscopic data. A few tens of seconds oftransmission from the Galileo NIMS or Mars ObserverVIMS instruments can exceed the total of all existingtelescopic spectra of the jovian system. An entirely newapproach is necessary, and some are now being testedin a few laboratories. However, one of our key findingsis that there presently exists an appallingmismatch between the objectives of NASA (andforeign) planetary missions to conduct highdata rate reflectance spectroscopy experimentsand the present capabilities for data analysisand interpretation.

We identify three critical research areas that requireimmediate attention in preparation for future planetarymissions.

Large Data Sets and the Merging of Spectraland Image Analysis. Future missions will obtainspectroscopic data in the form of three-dimensionalreflectance data arrays (image cube). As the spectraldimension is increased into the range of the 100 or morebandpasses necessary for spectroscopic interpretations,the problem of data management becomes acute. It isstill common, however, for scientists and programmanagers to treat spectroscopy and image analysisseparately. Although a few research groups areaddressing these problems, the level of effort within theplanetary reflectance spectroscopy program is low.

Enabling Instrumentation. Existing laboratoryand telescope observing facilities must survive if themission goals discussed above are to be achieved. Ofthe greatest urgency is the operation of existingspectrometers and other equipment. Funding fortechnical personnel is the greatest need in mostlaboratories, followed by support for maintenance andrepair of facilities. A few new specialized facilities areneeded.

Predictive Spectral Modeling. The goal ofpredictive spectral modeling is realistic in the view ofsome investigators familiar with recent developmentsin the field; however, the present level of effort in theprogram is modest, partly because techniquedevelopment is not a high priority of science proposalreview committees. Yet such an approach may be theonly way to analyze efficiently the large quantities ofdata expected from new missions.

Vulnerability of a Leveraged ProgramAttempts to maintain a balanced program with a

broad scope in the face of mission delays and constraintson the research budget appear to have resulted in aprogressive reduction of support for most individualinvestigators over the past 5 years, although newinvestigators were added and the proportion of thePlanetary Geology Program funding for this field wasapparently modestly increased. At the same time, thescientific and technical sophistication of the field hasincreased, thereby increasing the requirements forlaboratory facilities, computational facilities, telescopicinstrumentation, etc.

The reflectance spectroscopy effort is nowhighly leveraged, that is, high research output ispossible only because other NASA programs, othergovernment agencies, and universities are carryingmany of the real costs of planetary reflectancespectroscopy research. In the short term, shifting coststo other programs or institutions appears to be desirablebecause it results in more research per dollar for theNASA planetary program. This leverage, however, worksboth ways: control of the program passes to others who

do not necessarily share the objectives of the reflectancespectroscopy program. If the other programs defaultor change direction, the NASA planetary reflectancespectroscopy program is vulnerable.

Interface With Other Scienceand Program Areas

Because reflectance spectroscopy is a technique withinthe broader field of planetary science, it is essentialthat there be strong cross-disciplinary tiesamong the investigators. However, cross-disciplinarywork does not always fit conveniently within NASAorganizational and programmatic structures. ThePlanetary Astronomy Program handles much of theplanetary data set acquisition and the relatedobservational instrumentation support, but data analysisis the responsibility of the Geology and GeophysicsProgram or the Planetary Atmospheres Program.Geochemistry and extraterrestrial samples programs arealso involved. Program management can promoteefficient use of existing resources by encouraging andfunding consortia and cooperative researchprojects among scientists within the reflectancespectroscopy program, and including outsideinvestigators.

Tbday, NASA is involved in a very active terrestrialremote sensing program involving reflectancespectroscopy. The terrestrial program has in some waysexceeded the planetary program in capability and levelof effort. There is now considerable competitionbetween these programs for personnel and facilities. Werecommend that a specific effort be made tocoordinate the reflectance spectroscopy effortsin technique development in the planetaryprogram and in the terrestrial program.

We recommend that immediate measures betaken to improve communications between theNASA reflectance spectroscopy programmanagement and the mission-orientedactivities in NASA, especially Galileo and MarsObserver. It is not clear that the mission planners oreven the investigation team leaders are aware of theongoing research requirements in reflectancespectroscopy, or that NASA management has been fullyappraised of the mission reflectance spectroscopydrivers.

EducationUniversity programs are a fundamental part of the

NASA program, not only because of the science andtechnology produced, but also because new researchers,technical staff, and administrators are being trained. Yetthe tendency in most government programs when fundsare limited is to consolidate around government facilities.The NASA planetary program has resisted this tendencybetter than most agency programs. To train students,funding must be stable for a 3 to 5 year period, but

this has not always been the case. It is essential thatstudent training continue and that newresearchers continue to be brought into thefield.

Consequences of Funding Actions

For the past 5 years, although we have been told thatthe portion of the Planetary Geology Program fundingfor reflectance spectroscopy was modestly increased,the funding per investigator per year appears to havediminished. Furthermore, for the reflectancespectroscopy investigations planned for new missions(e.g., MOM/VIMS) measurement planning and dataprocessing budgets are a factor of 3 to 5 too low to carryout the required work; this load is historicallytransferred to the basic research program, where itcannot be borne. The highest priority must begiven to stabilizing the program, preventingfurther deterioration of the funding base, andbuilding that base to meet the missionrequirements of the near future.

We have identified possible scenarios for futuremanagement of the field:

Scenario 1. Continue the current downward trend insupport per investigator and continue to apportion thebudget cuts among investigators. It is the continuationof this trend that is of primary concern, for the broadscience coverage and balance of the program are atstake. The demands of future missions cannot be metthis way.

Scenario 2. A small increase in funding would stabilizethe program, keep pace with inflation, and allow fora maintenance mode in which the program is intact butresources are not adequate to meet the critical missionchallenges ahead.Scenario 3. If a substantial increase in support wereavailable, the program could be stabilized, and a newlevel of effort could begin on mission-related challenges.There would be a lag period of a few years for gatheringpersonnel and equipment. Some investigators have takenon other research commitments as funding hasdiminished in the planetary reflectance spectroscopyeffort, and these commitments will not be droppedimmediately.Scenario 4. A scenario unattractive to someinvestigators is the elimination of some investigators tomaintain level or increased funding for others. This isthe approach of consolidating around a few centers ofexcellence where facilities as well as investigators exist.In this case, it is difficult to maintain a balance, but itpreserves a core capability which can be built on when(if) funding increases.

It is essential that the investigators in thereflectance spectroscopy program work closelywith management to provide information andsupport. It is also important that investigatorscommunicate effectively as a group. An annual orbiannual meeting of investigators andmanagement to discuss research andprogrammatic problems, not to presentresearch papers, would be useful.

Chapter 2Purpose and Scope of the Workshop

IPurpose and ObjectiveThe workshop was commissioned by the Planetary

Geology and Geophysics Program of the NASA Officeof Space Science and Applications, Division of Solar Sys-tem Exploration. The purpose was to review the fieldof reflectance spectroscopy, particularly as it is relevantto the sponsoring Progam. The basis for the field, itscontributions, present conditions, and future directionsand needs were to be treated. The science and tech-nique were to be considered, particularly in light of theneed for future space mission support. The instructionswere to hold a workshop and in other ways foster com-munication among members of the community, solicitopinions, and prepare a written report presenting asummary of the community conditions and impressions.The objective is to provide the Program with materialbased on which informed programmatic and budget de-cisions can be made.

Scope and LimitationsThe scope of this report is limited to reflectance spec-

troscopy in the visible and near infrared regions andits application to remote sensing of planetary surfacesand atmospheres other than Earth. All aspects of thefield are covered: spacecraft, telescope and laboratorymeasurement capability, previous science results, cur-rent and future problems, analysis and interpretationcapabilities and techniques, and laboratory and theo-retical studies of material properties.

Several other fields are closely related to remote sen-sing; they are discussed briefly below. It is importantto realize that the relationships among all the remotesensing areas are symbiotic and complementary. No twotechniques produce (to any great extent) the same in-formation, but they do allow consistency checking.

Terrestrial remote sensingThe development of reflectance spectroscopy as a re-

mote sensing tool occurred first in the solar system ex-ploration program as applied to other solar systemobjects using ground-based telescopes. Application toair- and spacecraft-borne studies of Earth was recog-nized early, and development soon began, but in a waysomewhat isolated from the planetary effort; the twoprograms were carried out in different parts of the or-

ganizational structure of NASA and with differentphilosophies. Today there is greater overlap in person-nel, technologies, and philosophy, but the two programsare still administered separately.

The terrestrial program is now more advanced inflight measurement technology and available data sets.This trend probably will continue, because aircraftmeasurements can be made while NASA spaceprobelaunch capabilities are being regenerated. Nevertheless,reflectance spectroscopy technique and science as relat-ed to the terrestrial remote sensing program are nottreated in this study. The scientists and facilities of thetwo areas of application (planetary and terrestrial)should be more closely linked for the benefit of bothareas. This will require coordination within the NASAorganization.

Atmospheric studiesThe application of reflectance spectroscopy to the

study of the composition and physical properties ofplanetary atmospheres has been extensive and success-ful. Here we concentrate on scattering from solid sur-faces, but aerosols or clouds contain solid or liquidparticles and may show characteristic absorptions; thesame physics and theory apply. We refer to this areaoccasionally, but it is not treated in depth, and thereare serious omissions.

Emission spectroscopyIn the mid-infrared spectral region (about 5—50 in)

there are strong and complicated bands in the emissionspectrum of many geologically important minerals. Ab-sorption and emission features in this region of the spec-trum arise primarily from molecular and latticevibrations. This was realized before reflectance spec-troscopy gained wide attention. However, problems inunderstanding and removing the effects of the physi-cal properties of materials (e.g., particle size, packing)caused funding agencies to lose interest. Neverthelessemission spectroscopy as a remote sensing techniquehas strong potential for providing mineralogical infor-mation. In fact, such an investigation (TES) has been ten-tatively selected for the Mars Observer Mission. Emissionspectroscopy could become a very effective complementto reflectance spectroscopy; reflectance and emissionspectroscopy should probably be considered as tandeminvestigations, as has apparently worked out for the

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Mars Observer Mission. However, emission spectrosco-py is not so far developed as reflectance spectroscopy,and much more research is required to define its ulti-mate worth. It is not discussed further in this report.

Vacuum ultraviolet spectroscopyVacuum ultraviolet spectroscopy is concerned with

wavelengths shorter than about 0.2 fi, where commonatmospheric gases are strongly absorbing. For use inplanetary science, this spectral region has had to awaitthe development of observational facilities, such as theIUE (International Ultraviolet Explorer spacecraft) orSpace Telescope, situated above the obscuring at-mosphere. The interaction of high-energy photons withplanetary materials primarily involves strongly allowedelectronic transitions "(charge transfer, exciton, andvalence-conduction band excitations), resulting in veryhigh optical densities. Most of the reflected flux is thusfrom first surface reflections, with very little transmit-

ted component. For polished mineral surfaces in labora-tory measurements, spectral reflectance is diagnostic.However, in paniculate materials, spectral contrast issomewhat reduced, and the diagnostic features aresomewhat degraded. The major difficulty with the tech-nique in this spectral region is that the solar flux is verylow. With our present instrumentation, only the closeterrestrial planets can be observed with adequate signal-to-noise ratio.

Other remote sensing techniquesThere are other remote sensing techniques funded

under the Planetary Geology and Geophysics Program,including radar and radio thermal emission, that arenot treated here. The field of monochromatic imagingis not treated here because it is directed at morpholog-ical studies and is more appropriately the topic of a sep-arate report.

Chapter 3The Field of Reflectance Spectroscopy

IHistoryThe reflectance spectroscopy technique has been used

extensively only for the last 20 years because theradiation detector technology for measuring (withsufficient precision and spectral coverage) thereflectance spectrum of distant objects was not availablepreviously. Even so, attempts have been made since thebeginning of this century. When the ability to observesolar system objects effectively was developed, a wealthof observational data resulted; the theoretical andlaboratory work to improve the technique followedquickly.

The excitement of initial and continuing discoveriesusing reflectance spectroscopy resulted in an increasein the number of scientists developing and applying thetechnique and in the funds supporting the work. TheNASA Solar System Exploration Program was an earlysupporter and continues to support work in this field.

Reflectance spectroscopy is a very active andproductive technique which is applied using ground-based telescopes as well as laboratory and theoreticalinvestigations. Over 100 articles per year from about25 active workers in the field appear in professionaljournals. Major discoveries have been made, and muchof the early reconnaissance of several objects or objectsystems (e.g., asteriods) has been carried out (see chapter3). The technique and instrument development havebeen driven by the telescopic observations. Essentiallyall existing reflectance spectra remote sensing data setsfor solar system objects other than Earth were acquiredusing ground-based telescopes; a few sets have resultedfrom Earth-orbital telescopes.

With the success of the technique, nearly everyadvisory committee studying future planetary missionsin the past 10 to 15 years has recommended that areflectance spectrometer be included in almost everyproposed mission pay load. The technique is now con-sidered so important for flight missions that NASA hasdeclared it a facility experiment to be provided by theflight projects rather than by principal investigators, asis the spacecraft itself and as were the television imagingexperiments.

But reflectance spectroscopy has not yet played a rolein NASA solar system exploration program flightmissions because of (1) the increasingly long lead timeNASA requires for development and flight of spacecraftinstruments, (2) the lack of initiative for new

experiments caused by the great success of the imagingsystems of the early lunar and planetary missions, and(3) the hiatus in planetary missions resulting frombudget cuts and NASA priorities over the past 10 years.Nevertheless, a reflectance spectrometer was chosen forthe (later canceled) Lunar Polar Orbiter mission in 1975.It apparently was to be an instrument on the CometHalley flyby-lemple 2 Rendezvous mission, for whichinstruments were never formally selected after anannouncement of opportunity was circulated in 1976.In 1976, the Near Infrared Mapping Spectrometer(NIMS) experiment was chosen for the Galileo Project;the instrument has been built and is awaiting theeventual launch of the spacecraft (scheduled for 1989or 1991). The Mars Observer Mission (MOM) also hasa reflectance spectrometer (VIMS), selected in April1986. The Comet Rendezvous Asteriod Flyby mission(CRAF) announcement of opportunity described afacility reflectance spectroscopy instrument as a primecandidate for the payload, and Lunar Geoscience Orbiterand Cassini mission science working groups haveseriously recommended this investigation. Because ofthe impending mission involvement, the field ofreflectance spectroscopy has recently evolved as asubdivision of the planetary exploration program, andthe specific activities of the field have been tailored toaccommodate specific mission capabilities.

Reflectance spectroscopy has become increasinglyimportant in the area of terrestrial remote sensing. How-ever, the focus of this report is the use of reflectancespectroscopy in planetary studies.

A related area of remote sensing that was active 20years ago and has again become active is emittancespectroscopy. This field takes the general approach usedin reflectance spectroscopy farther into the infraredspecial region, where thermal emission is the dominantsource of radiation from planetary surfaces andatmospheres. Much of the reflectance spectroscopymeasurement and analysis approach still applies, andthe physics of the emission process is almost totallycontrolled by molecular processes. This area is nottreated here.

IScience FocusThe primary purpose of planetary geosciences (e.g.,

geology, geophysics, and geochemistry) and atmospheric

sciences is to determine the nature, origins, and historiesof the solid bodies and atmospheres of solar systemobjects. The majority of terrestrial geoscienceinvestigations rely on mineralogy as a criticalinformation source, and mineralogical information isequally critical to solar sytem object investigations.Specific mineralogy is not only a measure of the initialelemental composition of an object but also a directindicator of the thermodyamic conditions experiencedby at least parts of the object throughout its history.The molecular and particulate constituents in theatmosphere and exchanged with the surface are equallyimportant to the study of these objects.

Reflectance spectroscopy provides information on thetype and phase abundance of surface mineralassemblages and atmospheric constituents, and henceinsight into the history and processes operative for eachobject. Reflectance spectrophotometry also providesinformation on -the physical characteristics of thesematerials. In combination with other data sets, such aselemental compositions from gamma- and x-rayspectroscopy (which give elemental abundances), themineral properties derived from reflectance spectraprovide a powerful means of investigating planetaryobjects. Reflectance spectroscopy constitutes one of thevery few and sometimes the only remote sensingtechnique available for determining mineralogy of mostsolar system objects for the foreseeable future.

By characterizing an important subset of the surfaceand atmospheric constituents (mineral or cloud species,composition and abundance, gaseous species) ofplanetary bodies, reflectance spectroscopy provides abasis for extension of data derived from spacecraftlanding sites and from returned samples and meteorites.

The field consists of both science and technique, asis true of most experimental and measurement-orientedresearch. The science is a mixture of (at least) geology,geophysics and geochemistry, physics, and chemistryand is centered on determining the mineralogy andcomposition of solid objects and their atmospheres andworking out the physical and chemical processesoperating to create and alter them. This basicinformation is used by a wide variety of scientificdisciplines. A good understanding of the technique isrequired for the science to be properly done, and thetechnique itself is still subject to major improvementsand new measurement discoveries. Thus, students andprofessionals must be qualified in the use of thetechnique in order to contribute to the first-orderdevelopment of the field. The long-term goal is to makethe technique a straightforward analysis method easilyunderstood by nonspecialists. As long as the techniqueis effective and the information it provides is useful,there will be a need for scientists with a wide rangeof orientations, from nearly pure technique developmentto nearly pure science application.

The evolution of this field has reached the point at

which the name reflectance spectroscopy may no longerbe appropriate. The term reflectance spectrophotometrymay prove to be more desirable in recognition of thefact that future planetary exploration missions will re-turn both spectral and photometric information of highspatial as well as spectral resolution. Future spectralanalysis activities will expand beyond identification ofnew mineral species and will include determination ofabsolute abundances of particular species and phaseswithin a given spatial unit. For this more difficult goal,precise measurements of intensity are required.

IAreas of EffortThe primary planetary reflectance spectroscopy data

set results from the measurement of reflected sunlightfrom a planetary object and the calibration of themeasurement instrument and the conditions so that theratio of reflected to incident sunlight as a function ofwavelength (spectral reflectance) can be calculated. Thespectral reflectance of a particulate surface depends onmany factors; mineral type, chemical composition,abundance, and grain size are the most important. Mostminerals show diagnostic absorptions due to molecularvibrations, electron charge transfer, conduction bands,and electronic transitions. Second-order effects onabsorption band presence and wavelength positioninclude viewing geometry, particle packing, andtemperature. Other effects such as weathering (whichproduces other minerals) and sputtering can be majoror very minor. The magnitude of these effects dependson the exposure time, intensity, and the exact nature(i.e., mechanism) of the weathering and sputteringprocesses.

The technique of reflectance spectroscopy involves theinterpretation of the planetary reflectance spectra todetect these absorptions, to identify the mineral phasespresent, and, through available models (theoretical andempirical) to determine abundances and physical states.It can often work in the opposite sense, that is,determining what is not present on the surface of abody—a result of great significance in refining existingmodels and developing new models of surfaceproperties.

The theoretical models and laboratory measurementsof candidate materials from which the interpretationof the planetary data set can be derived are of primaryimportance. The fundamental data set used forinterpreting the planetary spectra and determining thecomposition of planetary surfaces is the laboratoryreflectance spectra of minerals, rocks, gases, and ices(which themselves are minerals) under simulatedplanetary conditions. The spectra of many hundreds of(planetary surface analog) materials have beenmeasured, allowing many of the discoveries cited inchapter 3. Theoretical models to calculate reflectance

10

spectra from basic material optical properties and theuse of examples from laboratory measurements arecritical for efficient interpretation of the coming waveof new data; laboratory measurement of all materialsunder all relevant conditions are time consuming,expensive, and virtually impossible.

The successful application of reflectance spectroscopyrequires contributions from four distinct and equallyimportant areas:

Development, operation, and maintenance oflaboratory, telescopic, and flightinstrumentation and related personnel andfacilities

Measurement and archiving of spectra andsupporting parameter data bases for solarsystem objects and candidate materials in thelaboratory, using telescopes, spacecraft, andlaboratory systems, to address well-formulated and significant scientific questionsor technique development needs

Development of reflectance spectroscopytheory, rigorously based on radiative transfertheory, along with interpretive calibrationsand procedures from which procedures canbe developed for deriving chemically,mineralogically, and geologically significantproperties from spectral data sets

Interpretation of the observational data setto determine the planetary surface andatmospheric properties and integration ofthose properties with other availableinformation into an appropriate model thataddresses the specific scientific issue raisedin the original statement of the problem thatmotivated the measurement

Instrumentation, interpretive calibrations, laboratorydata sets, and theoretical modeling are enablingtechnologies. They permit acquisition of spectral datafor solar system objects and interpretation of those datasets to derive surface mineralogic and physicalparameters and certain atmospheric properties. Prop-er data base management procedures must be followedto ensure that the data sets are and will continue to beuseful to the community at large. All these activities areessential to the successful application of reflectancespectroscopy to planetary science problems, and mostmust be carried out as integrated activities withparticipating scientists working in and familiar withseveral areas.

IMeasurement ConsiderationsThe fundamental measurement of reflectance

spectroscopy is the ratio of reflected sunlight to incidentsunlight on an area of a solar system object. Thismeasurement is made using detectors and wavelengthdiscriminating devices that (ideally) yield a spectrum oflight intensities as a function of wavelength, polarizationstate, location on the surface of the object, and therelative angular relation between Sun, object, andobserver at the time of measurement.

Reflectance spectroscopy depends on an illuminatingsource of light, which in planetary studies is the Sun.As a quasi-blackbody radiator at 6000 K, the Sun is anefficient radiator of energy in the near ultraviolet,visible, and near infrared spectral regions. However,somewhere in the spectral region between about 1.6and 5.0 ft. for the terrestrial planets (depending on thedistance of an object from the Sun), the planetary bodyitself becomes a radiator and emits as much or morethermal energy from its surface as the energy ofsunlight that it scatters back to space (see the figure).When the emitted energy becomes the major fractionof the reflected energy at a given wavelength,interpretation of the measured spectrum becomes dif-ficult to impossible. At ultraviolet wavelengths shorterthan about 0.4 ji the solar flux decreases rapidly.Therefore, the region of most interest covers the wave-length interval from about 0.3 n through about 5.0 /*,where reflected incident solar light is usually the pri-mary source flux from surfaces and atmospheres ofsufficient strength to be measured accurately.

IPhysical BasisThere is a direct link between the phenomenological

aspects producing reflectance (or absorption) spectraand the regions of the electromagnetic spectrum wherefeatures are observed. In the wavelength range 0.2—5.0(i, spectral features have origins involving electronic,vibrational, and rotational energy levels. Thesetransitions are further subdivided into anion-^cationelectron transfer (e.g., O "-*Fe +) in the near ultravioletregion, metal-^rnetal intervalence electron transitions(e.g., FeZ+—Fe or Ti -*>Ti in pyroxenes) in thevisible region, intraelectronic or crystal field transitions(e.g., t2g-»eg energy levels of 3d orbitals of Fe inolivines) in the visible near infrared region, andvibrational and rotational transitions of specificfunctional groups of molecules or anions that areobserved in the near infrared region as combination andovertone bands (e.g., H-O-H or CO2) or anions (e.g., O-H" or CO ) in, for example, clay silicates and carbonates.

In general, wavelengths (energies) of these transitionsare diagnostic of cations and their crystallineenvironments, or of functional molecular or anionic

11

groups, in minerals. However, additional theoreticalanalyses of spectra and energy levels, utilizing crystalchemistry, bonding models, quantum theory, andselection rules, are often required to aid the assignmentof features in reflectance spectra. On the other hand,laboratory spectral measurements of correlative mineralassemblages or rock types believed to be models ofsurfaces of planets have had to be made under physicalconditions simulating their regoliths. An ongoing re-search area is the measurement of spectra at differenttemperatures, confining (atmospheric) pressures,particle sizes, grain size packings, and modal mineralproportions. Thus, laboratory and theoretical calibra-tion studies are a prerequisite for detailed interpretationsof remote-sensed reflectance spectra.

The light scattered by a surface or atmosphere can be Ihe resull of a very complexinteraction. First surface reflections and diffuse scattering from several materialsof several grain sizes can be mixed in a single measurement for one resolution ele-ment. For many solar system materials, reflectance spectra can be considered asprimarily a function of the mineral or molecular species and their abundance andcomposition. For solid surfaces, the measurement usually involves only the upperfew millimeters of the surface material. These materials at ultraviolet, visible, andnear infrared wavelengths exhibit absorption features due to molecular vibrationsand lo electronic energy transitions of several types. This first-order effect is modifiedby a number of second-order effects, such as geometry and particle size, which usuallyalter Ihe spectral properties only in a way slowly varying with wavelength. Thereare materials which are important exceptions, such as various ices and oxide minerals,where particle sizes have a major first-order effect on the absorption band proper-ties in the spectrum. Thus the problems of complex scattering and mixtures belowthe spatial resolution element are very important, sometimes making it impossibleto separate atmospheric and surface effects.

EMITTEDTHERMAL

REFLECTEDSOLAR

ASSUMED'I Km2 MARE AT SUBSOLARPOINT; MEAN EARTH-MOONDISTANCEPHASE ANGLE » O"T = 3 9 5 ° KE M I S S I V I T Y = 1.00

2 3 4

WAVELENGTH

RADIATION FROM MOON [ikm2 of more] AT EARTH

12

Chapter 4Contributions

Surface composition and mineralogy of a solar sys-tem object are fundamental properties that must be de-termined in order to understand the history and originof the body. Reflectance spectroscopy has proven to bethe most powerful available technique for determiningthick atmospheric and surface lithologic compositionby remote sensing. Planetary scientists using Earth-basedtelescopes and spectrometers have used this techniqueto determine the primary surface and atmospheric con-stituents of all the major bodies in the solar system, fromthe nearby Moon to distant Pluto. Essentially everythingwe know about surface mineralogy, except for Earthand the Moon, for which we have documented samples,has resulted from reflectance spectroscopy used as aremote sensing tool and with ground-based telescopes.

The basis for the credibility of the technique lies inboth past discoveries of planetary surface and at-mospheric properties and confirmation of predictionsby groundtruth. These are discussed below.

IDiscoveriesThe major scientific contributions made to planetary

science through the use of reflectance spectroscopy andrelated techniques, such as multicolor photometry andpolarimetry, are many and varied. Perhaps the most ef-fective way of communicating the extent and nature ofthese contributions here is to simply list examples.

MercuryLunar-like surface regolith (1960)Low ferrous-iron crust (1975)Spectrally distinct surface units (1975)Sodium emission (1985)

VenusCarbon dioxide atmosphere (1932)Isotopic forms of CO2 (1962)CO, HC1, HF in atmosphere (1967)Sulfuric acid in clouds (1973)Sulfur in clouds (1975)Sulfur dioxide in atmosphere (1979)Highly oxidized surface materials (1986)

MoonNo atmosphere (1859) [using polarization data]

Surface rough and loose (1865)Basaltic surface (1908) [confirmed in 1963 and

1968]Spectrally distinct surface units (1918)Surface very porous (1918) and fragmental (1945)Surface is impact debris, glassy, some iron (1953)Surface darkens with age (1955)Surface particle sizes to 0.3 pi (1960) [polarization

data]Solar wind darkening (1962)Large amount of opaque phases (1963)Dominant particle sizes about 10 /t (1963)Olivine or clinopyroxene present (1968)Vitrification darkening by impacts (1970)Major highland rock units defined (1972)Existence of many units unsampled by Apollo

(1978)Olivine-rich material in some central peaks (1982)Existence of ancient, pre-basin basalts (1983)Anorthosite deposits in Orientale and Nectaris ba

sin rings (1984)Near-side crust is laterally and vertically in-

homogeneous (1986)

MarsSurface of Fe-oxide and silicates (1961)Carbon dioxide in atmosphere (1966)Hydrate and water-ice on surface (1969)Clay minerals in atmospheric dust (1971)Mafic silicates on surface (1972)Carbon dioxide ice at south pole (1976)Water ice at north pole (1979)Mg-OH and clays on surface (1981)

AsteroidsParticulate surfaces (1964)Vesta is a differentiated body with basaltic surface

(1970)Many distinct compositional classes (1971)Some composed of meteorite-like mineral assem-

blages (1975)Some dynamic families have common parent bod-

ies (1977)Radial distribution of classes in belt (1982)Some asteroids are olivine rich (1983)Some have mineralogically distinct surface units

(1983)

13

Near-Earth asteroids a different populationOrganic-rich composition of some asteroids (1984)Metamorphic heating declines rapidly with solar

distance (1985)FeO content increases rapidly with solar distance

(1986)

Giant PlanetsMethane and ammonia in atmospheres (1930s)Hydrogen atmosphere (1960)Vertical cloud structure and particulate properties

(1960?)Stratospheric hydrocarbons (late 1960s)D/H ratios in Jupiter (1972)CO in stratosphere of Jupiter (1975)

Satellites of Jupiter (Galilean)All have leading/trailing spectral asymmetry (1927)lo

No water ice (1972)Sulfur rich (1973)Sodium cloud (1973)Sulfur dioxide gas and ice (1979)Longitudinal distribution of SO2 (1980)Albedo-temperature relationship for hotspots

(1985)Europa

Water ice (1972)SO2 on trailing side (1981)Sulfur on trailing side, magnetospere modifica-

tion (1985)Ganymede - water ice (1972)Callisto - water ice (1972)Hemispheric dichotomy in surface (1975)Magnetospheric effects on trailing hemispheres

(1981)

Satellites of SaturnMethane on Titan (1948)Complete cloud cover on Titan (1972)Water ice surfaces (1975)Bright hemisphere of lapetus is water ice (1976)Dark hemisphere of lapetus "carbonaceous rich"

(1983)

Satellites of Uranus and NeptuneSurface water ice (1980)Dark carbonaceous-like component (1983)Methane ice, solid or liquid nitrogen on Triton

(1984)

Rings of SaturnWater ice (1970)Dark non-icy component (1973)Dark component may be carbonaceous (1980)

I

Rings of UranusVery low albedo, non-icy (1977)

Rings of JupiterLow albedo, non-icy (1980)

CornetsEmission lines from CN, C2, C3, (1882)Emission from OH (1943)Emission from ionized water (1974)Neutral water (1985)Organic compounds (1986)

PlutoMethane ice (1976)Methane gas (1980)

GroundtruthGroundtruth is important to the effectiveness of re-

mote sensing techniques both for confirming and refin-ing the techniques and for allowing the extension ofmore sophisticated interpretations of unsampled loca-tions. Except for Earth (which we exclude from this dis-cussion), we have documented surface material samplesonly for the Moon. Although reflectance spectroscopywas not sophisticated when the Apollo program beganproducing samples, it was possible to make predictionsabout the mineralogy of landing sites before sampleswere returned. In particular, the prediction of the titani-um content (in ilmenite) of the Apollo 17 site was suc-cessful and helped confirm the technique. Well beforethe Apollo program, predictions from lunar colors andearly spectra called for a basaltic surface material. In1967, the importance in the lunar mare soil of pyrox-ene with a Hedenbergite composition was predictedfrom spectra.

Meteorites are now accepted as samples of asteroids(with a few exceptions), with the clearest associationsbeing in the .cases of basalt meteorites (Vesta) and dunitemeteorites (class A asteroids). In general, it appears thatlarge biases exist in delivery of meteorites to Earth, sothat some important classes of asteroids have not beenincluded in sample studies.

Experiences from both the Viking mission to Mars andthe Voyager mission to the Galilean and outer solar sys-tem satellites in general show that reflectance spec-troscopy measurements and most of the interpretationsare at least reasonable. In a sense, these missions provid-ed a measure of groundtruth by at least relativelycloseup observations at higher spatial resolution (butlower spectral resolution and reduced spectral range)that confirmed earlier Earth-based observations. In fact,some "discoveries" commonly attributed to these mis-sions were actually made years before by spectrosco-py from Earth. However, the lack of any direct surfacemineralogy investigation on these missions makes com-parisons difficult.

14

ISummaryLaboratory spectroscopy of terrestrial minerals and

rocks, various gases, frosts, ices, and synthetic com-pounds, and extraterrestrial materials such as meteor-ite and lunar samples have shown that there arediagnostic features that allow discrimination of themineral assemblages on planetary surfaces and henceprovide insight into the composition of these objects.Most meteorite mineral assemblages have been foundon asteroids, and our knowledge of meteorite materi-als has been extended to specific places in the solor sys-tem. The bulk of lunar sample spectra are for Apollolanding site soils and provide good background for un-derstanding the alteration and agglutinate formation

process of the lunar environment. Minerals that havebeen identified spectroscopically in lunar soils includelow-Ca pyroxene, high-Ca pyroxene, plagioclase, olivine,Fe-bearing glass, and Fe- and Ti-oxides (opaques). Thisinformation provides a basis for mapping widespreadareal units on the Moon using telescopic surveys, infor-mation otherwise presently inaccessible. This is just oneexample of how reflectance spectroscopy should be in-tensely applied to all bodies in the solar system. Withmost of the solar system unexplored, the vast bulk ofthe work in the new field of planetary spectral reflec-tance remains to be done. In future decades more dis-coveries will occur, and fundamental spectralinformation needed to understand the origin and evo-lution of the solar system will develop.

15

Chapter 5Current Capabilities and Resources

I

This chapter presents a list and short description ofthe existing capabilities and facilities of research centerswhich are utilized for planetary studies using reflectancespectroscopy. These are given in terms of (1) the abilityto derive information from measurements and (2) thefacilities and personnel to make the measurements andto interpret them. The interpretive capabilities arepresented according to the goals and objectives of thefield and the degree to which they have been achieved.The facilities and personnel are discussed by identify-ing the principal research centers and outlining the re-search topics treated at each, as well as by listing thefacilities available for reflectance spectroscopy at eachresearch center. Much of the information is presentedin table or matrix form to make it easier to comprehend.

This report should be used to evaluate the scope anddirection of the community as a whole and not to re-view individual research centers. Individual investiga-tors are not identified. Full evaluation of the field isbeyond the scope of this study. These summaries andoutlines are reasonably comprehensive, but because thematerial has not been fully reviewed, there are proba-bly some errors and omissions.

It must be noted again that there were severe limita-tions on the scope of this study, and areas such as ter-restrial remote sensing are not considered here.

Objectives and StatusThe goals and objectives of reflectance spectrosco-

py are discussed in chapter 3. An attempt is made hereto review the current capabilities for deriving scien-tifically useful information for solar system studies us-ing the reflectance spectroscopy technique bydescribing the degree to which these goals and objec-tives have been met. The objectives are listed in or-der of increasing difficulty:

Identify the presence of specific materialsand map their distribution.Determine the abundance of materialspresent.Estimate the composition of materials.

The current status of the accomplishment of theseobjectives and the goals to be pursued in the future are

outlined by objective in, respectively, tables 1, 2, and3. It can be seen from these three summary tables thatthe current and anticipated capabilities address fun-damental questions about the nature of the solar system.

IFacilities and PersonnelTo achieve the goals and objectives described in chap-

ter 3 and above requires three closely interrelated dataacquisition and analysis activities:

Obtain reflectance data for planetary sur-faces through a well-planned data acquisitionprogram (ground-based and Earth-orbital tel-escopes and deep space probes).Establish a solid foundation of laboratoryreflectance spectroscopy measurements formaterials and conditions appropriate for thesurfaces studied.Develop accurate theoretical and applied anal-ysis capabilities to interpret the data and ex-tract the desired information.

Each of these activities must be motivated by basic scien-tific questions about the solar system. This is an ex-perimental science, and it is measurement oriented.Measurement, however, should never be an end in it-self but rather a means to answer a scientific question.

These activities require the development, main-tenance, and operation of adequate facilities (telescop-ic, laboratory, computer, technical personnel, etc.) tocarry out the data acquisition and analysis objectives.A deficiency exists. There is no separate funding or pro-gram base to cover facility support. Budget line itemscovering this need which are included in researchproposals are routinely cut by review committees. A for-mal program is needed to provide long-term (3 to 5years) stable support for basic facilities at designatedcenters of excellence.

Many research centers have research goals and facil-ities that are involved with and funded by other (non-planetary or even non-NASA) programs. The planetaryresearch pursued by these groups is often heavily ortotally subsidized by other programs and agencies.Therefore, it should not be assumed that all or even

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most activities, facilities, and personnel mentioned inthe following sections are funded directly by the Plane-tary Geology and Geophysics Program. The communi-ty is in fact highly leveraged in that a little support fromthe Program is buying much capability. Slight decreasesin support by the Program could result in major lossesin capability, as researchers can no longer extend theirsupport under other programs without jeopardizingthose programs.

Participating Organizations andPrincipal Programs

There are at least 18 university, NASA center, and U.S.Geological Survey locations at which at least one inves-tigator is active in reflectance spectroscopy research asapplied to planetary studies. These research programsvary greatly in size and breadth. About half of the pro-grams have only one investigator. The total number ofinvestigators is about 30, and many of these do not de-vote full time to this area.

Table 4 summarizes these organizations and the prin-cipal research topics. None of the programs encompass-es all the areas required in the field, nor should they.There is considerable interaction among individuals andresearch centers concerning research topics andprograms.

Because the field is young, many investigators con-tinue to communicate with their home center after leav-ing. The small size of the community and the restrictionin funds, especially recently, has resulted in very littleoverlap in facilities and research programs amonggroups.

Planetary Spectrum MeasurementFacilities

The acquisition of reflectance spectroscopy data de-pends on the capabilities of instruments on Earth-basedor Earth-orbiting telescopes and on future instrumentscarried on planetary spacecraft. These facilities producethe primary data required to investigate the nature andcomposition of planetary surfaces. The informationabout solar system materials derived from the correctinterpretation of these data is the reason for the exis-tence of this field of planetary science. The capabilityof these facilities and the quality of the data they pro-duce thus control developments in the rest of the field.The measurements made using these facilities are guid-ed by scientific questions and by the technology thatcan be incorporated into the facilities.

Essentially all the reflectance spectra for planetary ob-jects have been obtained using ground-based telescopes.No U.S. spacecraft has carried a reflectance spectrom-eter to a planetary object. The only U.S. spacecraft thathas made planetary spectral reflectance measurementsis the IUE. Thus, it can be argued that the ground-based

telescope facilities are the most important to the fieldat this time and for the next several years, until the SpaceTelescope and the Mars Observer begin returning data.In fact, the Space Telescope does not have an instru-ment in its first payload to measure reflectance spec-tra other than in the ultraviolet and blue spectralregions.

There are only two centers at which major ground-based telescope facilities are actively used for reflectancespectroscopic studies of solid surfaces (University of Ar-izona and University of Hawaii). The Jet PropulsionLaboratory has significant facilities but most of theirobservations in the recent past have been made withthe Hawaiian facilities. Current planetary data acquisi-tion facilities are summarized in table 5.

Laboratory SpectrumMeasurement Facilities

The measurement of the optical properties of candi-date and sample materials for solar system objects iscritical for interpreting the planetary data set. It pro-vides comparison spectra of known materials for directinterpretation of spectra for unexplored planetary sur-faces. It provides fundamental data on physical and op-tical parameters required for use in theoretical modelsfor calculation of reflectance spectra. It also can be usedto create model data sets, which are necessary for de-veloping and testing the computer and automated dataprocessing and analysis systems required by the nextgeneration of primary planetary data, from imagingspectrometers.

This laboratory measurement capability has grownthe most of the various facilities for reflectance spec-troscopy research in the recent past. This is becausethere is so much to be done. There are so many cate-gories of materials to be studied: ices, frosts, hydrates,organics, salts, silicates, oxides, metals, etc. There is suchvariety in the conditions under which they must be stud-ied to be relevant: cold temperatures of outer solar sys-tem objects, high temperatures of the surface of Venus,atmospheric conditions on Mars, radiation conditionsof the Galilean satellites, volatile environment of the sub-surface of Mars, conditions of cometary nucleus sur-faces, etc. This requires a wide variety of laboratoryfacilities: environment chambers of many sorts in whichconditions can be controlled while measurements aremade, irradiation systems, spectral coverage over a widespectral range requiring several different detector anddispersion technologies, goniometers, microsample sys-tems, etc. These are probably too complex for any oneinstitution. Capabilities are needed for detailed studiesof the spectral reflectance properties of materials (un-der both diffuse and bidirectional geometry) as well asfor studies of the general photometric properties of sur-faces. In addition, these facilities must have data process-ing capabilities to reduce and analyze the measurements.

18

The capabilities of existing research facilities availa-ble to planetary scientists are summarized in table 6.There are at least 13 research centers with laboratoryreflectance spectroscopic measurement capability, andat least 9 of these have only one investigator active inreflectance spectroscopy. At least 5 research centers re-port no capability. The facilities in table 6 overlap verylittle in application focus; these facilities are heavily used.

Planetary Spectrum Data SetsCurrently available spectral reflectance data for plane-

tary surfaces have been obtained almost completelythrough the use of Earth-based telescopes. This will con-tinue to be the case until the Mars Observer returnsdata in 1991, followed by Galileo, CRAF, and the Observerseries LGO, NEARS, etc. The existing and expected newtelescopic data sets are critical to planning the new mis-sion investigations as well as preparing the data han-dling systems and the interpretive techniques for thedeluge of data expected.

In addition to the telescopic spectra, there are a fewMars reflectance spectra in the infrared for wavelengthslongward of about 2.5 /* from the Infrared Spectrome-ter (IRS) investigation on Mariner Mars 6 and 7. Also,the International Ultraviolet Explorer flUE) Earth-orbitalspacecraft has produced a large number of ultravioletreflectance spectra of the Galilean satellites and comets.

There has been no formal (Program) organization ofthe available reflectance data of planetary surfaces; how-ever, individual investigators have imposed an informalstructure. Many data sets are now being restored, main-ly at the University of Hawaii, where most of them wereacquired, as part of the Planetary Data System program.There are significant spectroscopy data sets for almostall planetary objects; the largest are for the Moon, Mars,and asteroids. The principal planetary spectroscopy datasets are maintained at the University of Hawaii, theUniversity of Arizona, the Jet Propulsion Laboratory,and Brown University.

Laboratory Spectrum Data SetsPreliminary surveys of the spectral properties of so-

lar system materials exist for terrestrial, lunar, andmeteoritic samples and for rocks and minerals, con-densed volatiles, and frosts. These data provide a foun-dation for interpretation of planetary data. However, ameasure of the wide range of conditions of these datasets is the fact that no meaningful summary of the ex-isting data sets could be prepared for this report.

Many data sets do not contain sufficient characteri-zation of the materials and are thus inadequate for therequirements of applied reflectance spectroscopy overthe next decade. Laboratory measurements were oftenmade for specific applications and not to support a data-base. Only certain spectral ranges were covered, andinformation on sample and measurement conditions wasnot recorded. More attention should be paid to properly

characterizing samples and measurement conditionsand to placing the data in a standard format. This li-brary task is just one of many that have been uncoveredby the Planetary Data System effort. A committee com-posed of members of the spectroscopy communityshould be formed to promote better archiving and re-trieval of laboratory reflectance spectral data sets.

New laboratory measurements of materials will be re-quired for future investigations. These should be madeat several laboratories and should focus on the needsof specific research programs. Theoretical modelsshould be used to extend laboratory measurements andto help avoid massive and detailed measurement pro-grams. The measurements should be archived for gener-al use.

Spectrum Analysis CapabilityThere are several types of spectrum analysis capabil-

ities: computer hardware and operating systems, dataprocessing and analysis software systems, and interpre-tive techniques and algorithms. All research centers in-volved in reflectance spectroscopy research must havespectrum data set handling capabilities.

The computer facilities being used for theoretical andapplied analysis projects using reflectance spectrosco-py are summarized in table 7.

The software data handling system is especially im-portant, particularly for the large imaging spectrome-ter data sets expected from ground-based telescopes andspacecraft instruments and for the associated labora-tory data libraries. Several integrated systems have beendeveloped specifically for reflectance spectrum handling.SPECPR, which deals with single spectra, was developedto handle one-dimensional data sets. It is maintained atseveral centers, and exchange of developments is fairlywidespread. Image cube data processing systems (GARPand SPAM) have also been developed. These systemshandle the data sets produced by imaging spectrome-ters and deal with image cubes as well as with imageplanes and individual spectra. GARP and SPAM havebeen exchanged between the development centers andare running in a preliminary fashion at one or two othercenters. There is a need for innovative analysis of datasets using "artificial intelligence" techniques.

The current status of interpretive capability is moredifficult to summarize, since reflectance spectroscopyis not a "black box" science, for which every input hasa uniquely interpretable output. Although analysis hascertainly progressed well beyond simply "matching"spectral curves, a number of areas need considerableeffort and testing, especially to obtain the second andthird objectives of reflectance spectroscopy (tables 2 and3) which provide the type of quantitative informationnecessary to address many geochemical problems.

InvestigatorsThe individuals participating in spectral reflectance

19

research applications are the most important assets ofthe field. The number of scientists and students activelyworking on spectral reflectance applications in plane-tary science are summarized in table 7. Approximately30 investigators are currently using reflectance spec-troscopy for planetary studies. Only two researchcenters have three or more investigators. This indicatesa rather thin spread of personnel, with the associatedrisk of too little communication, especially since manyof the investigators have unique areas of specialization.

About seven of the research centers currently trainstudents for work in the field. The average number ofnew Ph.D. researchers from all education programs is

estimated to be one to three per year. Not all or evenmost of these students enter the NASA PlanetaryProgram.

Very few investigators receive all their funds fromplanetary investigation programs; some are unfunded.A large percentage of participants contribute their ef-forts to the Planetary Program at a level much higherthan that of their funding by the Planetary Program.This highly leveraged involvement carries with it aninherent lack of stability for the planetary reflec-tance spectroscopy community and the planetaryprogram as a whole.

Table 1. Detection and Identification of Specific Materials

Planetary Body Status Goals

Mercury Surface properties appear to be similar to Moon;no specific minerals identified yetNa in atmosphere, presumably sputtered fromNa-bearing minerals in the regolith

Moon3 Pyroxene, olivine, Fe-Ti-bearing glass detectedPlagioclase detected in basaltic mareShocked and unshocked plagioclase(anorthosites) identified in highlandsAgglutinates detected

Mars Fe3+-bearing phases and amorphous ferricoxides detectedPyroxenes detected locallyOlivine suspectedClay minerals detectedCrystalline ferric oxides can be detected (ifpresent)H2O frost detectedDust characterized

Asteroids Pyroxene, olivine, plagioclase detectedOrganic polymers suspectedOpaques detected qualitativelyOH detected

Metal suspected

Outer SO2 detected on loSatellites Sulfur component detected on Europa,

suspected on loH2O frost detected (± unknown contaminants)on Europa, Ganymede, Callisto, Tethys, Dione,lapetus, Rhea, Enceladus, Hyperion, Miranda,Ariel, Umbrial, Titania, OberonCH4 detected on Pluto, probably on TritonN2 (solid or liquid) probably detected on Triton

Identify the minerals and any alterationproducts of the surface

Resolve superimposed features of low- andhigh-Ca pyroxene, olivine, and plagioclaseDetect Fe-bearing glass (low-Ti)Confirm detection of plagioclaseDetect ilmeniteDetect Ti3+-bearing pyroxenes and glasses inmare basalt regions

Resolve superimposed features of pyroxene,olivine, and atmospheric bandsDetermine characteristic properties ofplagioclase and opaques for Mars materialIdentify mineral compositions and structuresof clay mineralsDistinguish overlapping features of H2O (iceand adsorbed) and atmospheric CO2Search for minerals hosting SO^- anfj

CO3 anionsDetermine nature of oxide and oxyhydroxidephases, especially <100 nm

Distinguish differentiated metal from chondriticmetalUnderstand physical state of metal in regolithsResolve superimposed features of low- andhigh-Ca pyroxene, olivine, and plagioclaseDetermine relative abundance andcomposition of silicates and organics and thepresence and amount of hydrates and water

Identify silicate, carbonaceous, and othercomponentsIdentify other volatiles and frosts, e.g.,presence of mixtures such as NH3+H2O,form of sulfur and sodium on lo, irradiationproducts

By remote sensing for unsampled localities, not from returned samples.

20

Table 2. Determination of Abundance of Materials

Planetary Body Status Goals

Mercury

Moon

Mars

Asteroids

Low ferrous iron content of surface

Relative abundances of olivine measuredRelative abundance of pyroxene measuredUpper limit of pyroxene determined for highlandfresh surfacesRelative maturity described locally (agglutinatecontent)

estimatedLower detection limits set for some minerals:

clay silicate minerals <+5%crystalline and magnetic ferric oxides <1%

OuterSatellites

Relative abundance of orthopyroxene and olivineestimated to ±5%

Quantitative mapping of S02, sulfur, sodium onloWater abundance estimated to ±10% on icybodies

Quantify amount and type of silicatesDetermine mineralogy of regolithIdentify source mineral of Na

Determine modal abundances for unsampledareas with the following precision:

pyroxene +5%olivine +10%plagioclase:

anorthosites identified and mappedother rock types ±10%

glass (Fe bearing) ±10%glass (Ti3+ bearing) ±10%opaques ±2%alteration products (agglutinates) ±10%

Map local and global surface composition

Determine modal abundances with thefollowing precision:

pyroxene ±5%olivine ±10%plagioclase ±10%clay silicates ±5%carbonates, sulfates, nitrates ±5%opaques ±5%sulfur compounds, specifically sulfate

minerals ?H2O frosts ±5%alteration products ±10%

Clarify hydroxylated minerals (clay silicates,iron oxyhydroxides, basic ferric sulfates)Map local and global surface composition

Determine amount of waterDetermine silicate/metal ratioIdentify specific carbonaceous chondriteclassesDetermine FeO/(MgO + FeO)

Determine silicate/frost ratioDetermine relative proportions of differenttypes of silicatesDetermine relative proportions of differenttypes of frosts

21

Table 3. Composition of Materials and Nature of Alteration Products

Material Status Goals

Pyroxene

Olivine

Plagioclase

Glass

Oxides

General systematics identified in early 1970s:Ca/(Ca+Fe+Mg) ±5%Fe/(Ca+Fe+Mg) ±10%

Compositional variations only defined accuratelyfor transmission spectra

Strength of plagioclase band is known todepend on FeO content

Absorption characterictics of Fe and Ti bearingglasses have been measured for terrestrial andlunar materials

Much is known about absorption characteristicsof crystalline and amorphous iron oxides; theconditions under which they are produced havebeen investigated, but are not well understood

Should be updated with more preciseanalytical techniques

Derive Mg/(Fe+Mg)

Resolve ambiguity between abundance andFeO contentDerive FeO content of feldspar

Calibrate Fe, Ti variations for reflectancespectraUnderstand vitrification and devitrificationprocesses and products for various surfaceenvironmentsUnderstand conditions and variations ofimpact melt

Determine the proportions of mixtures ofamorphous and crystalline iron oxidesDetermine the conditions under which theyare developed

AlterationProducts onPlanetaryBodies

Status Goals

Moon

Mars

Asteroids

OuterSatellites

Complex glass-welded aggregates (agglutinates)are the principal alteration products of theregolithTiO2 content can be estimated for mature maresoils to ±2% (±1% relative)

Global dust is fine-grained (<10 n) weatheringproduct of mafic silicates

Fine-grained regolith exists.Its nature is unknown, but the presence ofsignificant agglutinates is not expected

Regolith contains fine-grained frosts

Determine the effects of shock on mineralpropertiesDistinguish breccias, impact melt, and lithicassemblagesEstimate FeO content of mature soilsEstimate Fe and Ti content of pyroclasticglasses

Determine the nature and origin of global dustDetermine the sources, sinks, and distributionof global dustClarify the sulfate-bearing minerals anddelineate water or hydrated minerals in thepermafrostGeneral mineralogy (acidic - basic) of volcanicflows)

Determine alteration products of the radiationand impact environment on asteroid surfaces

Determine the effects of irradiation (ion,ultraviolet, etc.) and vacuum weatheringDetermine the effects of cumulative impactprocesses (macro and micro)Determine the nature (meteorite, cometary) ofthe impacting material in the outer solarsystemDetermine the minor components (clathratesand hydrates) in water frost surfaces

22

Table 4. The Role of University and Government Centers in Reflectance Spectroscopy

Center Contribution

University ofArizona

Brown University

Cornell University

GoddardSpace FlightCenter

Hawaii Institute forGeophysics,University ofHawaii

Jet PropulsionLaboratory

Johnson SpaceCenter

University ofMassachusetts

University ofMaryland

MassachusettsInstitute ofTechnology

University ofPittsburgh

RensselaerPolytechnicInstitute

U.S. GeologicalSurvey (Denver)

U.S. GeologicalSurvey (Flagstaff)

Measurement of transmission and reflectance spectra of frozen volatiles for application toouter solar system problems

Derivation of absorption coefficientsBidirectional reflectance measurements of lunar and terrestrial materialsDeconvolution of mineral mixturesAcquisition and analysis of telescopic spectra for unexplored lunar areasInvestigation of regolith development on lunar and asteroid surfacesAnalysis of venusian surface spectra

Phase function studies of spacecraft dataLaboratory phase function measurements

Infrared spectroscopy on megaelectronvolt irradiated samples of low temperature comet-icemixtures

Development of advanced mapping and point spectrometer instruments and analysissoftware systems, especially for spectrum and image cube data processing

Acquisition and analysis of telescopic spectra of Mercury, Moon, Mars, outer satellites,and asteroids

Bidirectional reflectance measurements of analog materials including silicates, metals, andvolatiles under a wide variety of environmental conditions

Implantation of S and SO2Spectrum database management and networkingDevelopment of analysis software for mapping spectrometer dataAcquisition and analysis of telescopic spectra for asteroids, outer satellites, and

atmospheric cloudsSpectrogoniometric and diffuse reflectance measurements of sulfur, frosts, and mixtures

of minerals and icesProton and ultraviolet irradiation of minerals, rocks, sulfur, and icesTheoretical analysis of phase functions

Bidirectional reflectance measurements of Mars analog materials with a focus on theproperties of iron oxides and oxyhydroxides

Acquisition and analysis of reflectance spectra of asteroids and MercuryDevelopment of automatic analysis capabilities, including extraction of absorption band

information from reflectance spectraWeathering processes on Mars

Acquisition and analysis of asteroid and comet spectra

Spectral measurements of minerals, glasses, colloids, and mixtures of these (100-600 K)Theoretical calculations of molecular orbital energy levels to aid assignment of energies

and intensities of spectral features observed in reflectance spectra

Develop reflectance spectroscopy theoryApplication and testing of theory for planetary data (Moon, Mercury, asteroids, satellites)Supportive laboratory studiesEffects of melting, vaporization and kiloelectronvolt ion irradiation on optical properties of

mineralsDerivation of interpretive spectral calibrations appropriate for asteroids for investigations of

the thermal and collisional evolution of the early planetesimal populationAcquisition and analysis of time varying (rotational) asteroid spectraDetermination of the fundamental properties of carbonate spectraDevelopment of fast algorithms to derive mineral abundance and grain size information

using reflectance theory and optical constant informationAnalysis of icy satellite spectra

Multispectral image data analysis and map makingDevelopment of computer data processing software systems and techniques for

multispectral image analysis and cartography

23

Table 4. The Role of University and Government Centers in Reflectance Spectroscopy (continued)

Center Contribution

University ofVirginia

WashingtonUniversity

University ofWashington

University ofWyoming

Kiloelectronvolt ion irradiation of low temperature condensed gasesMaterials analysis, including infrared spectroscopyMegaelectronvolt ion work in conjunction with AT&T Bell Labs

Efficient management of imaging spectrometer data

Merging of reflectance spectrophotometry with multispectral imagingDevelopment of algorithms to compare image spectra with laboratory reference spectraDevelopment of spectral mixing models that cover composition, particle size, and lighting

geometry variations

Development of analytical models for complex mixtures

Table 5. Facilities for Obtaining Planetary Reflectance Spectra

Location X. range (M) X resolution Comments

TelescopesHIGHIGHIGHIGUAUAIRTFIRTFMcDpossibleJPL/IFAHIG

SpacecraftIUEGalileo

0.35-1.00.6-2.62.0-5.01.0-5.00.3-2.50.3-1.00.8-5.01.0-5.00.3-1.0

future:1.0-2.50.2-5.0

0.1-0.30.7-4.0

1.5%1.51.5-3.0<~1%? High? High~3%--1-1/3%1%

1/2%<~1%

High0.5%

Circular variable filterCircular variable filterCircular variable filterGrating imaging spectrometer (being tested)InterferometerCCD; grating spectrometerCircular variable filterGrating arrayCCD; grating spectrometer

Prism spectrometer (proposed)Grating imaging spectrometer (augmentation

Grating spectrometerScheduled to fly 1989 or 1991; will measure

of above device under way)

satellites of Jupiter as well as

Mars 0.35-4.3 or 5 ~1%Observer

Lunar Geochemical ObserverComet Rendezvous/Asteroid FlybySpace 0.1-0.7 High

Telescope

asteroid (flyby); data in 1 to 5 years after launchScheduled to fly 1990; data in 1991/92

Mapping spectrometer being planned; mission anticipated; data in 1992/3Spectrometer being planned; mission anticipated; data in mid-1990sHigh resolution grating spectrometer

Abbreviations:HIG Hawaii Institute for Geophysics, University of HawaiiUA University of ArizonaIFA Institute for Astronomy, University of HawaiiIRTF NASA Infrared Telescope Facility, Mauna Kea Observatory, HawaiiJPL Jet Propulsion LaboratoryMcD McDonald Observatory, University of Texas

24

Table 6. Facilities for Laboratory Spectral Reflectance Measurements

Institution

University ofArizona

BrownUniversity

CornellUniversity

Goddard SpaceFlight Center

Hawaii Instituteof Geophysics

Jet PropulsionLaboratory

Johnson SpaceCenter

University ofMassachusetts

MassachusettsInstitute ofTechnology

University ofPittsburgh

RensselaerPolytechnic Institute

U.S. GeologicalSurvey (Denver)

University ofVirginia

University ofWashington

instrument

Type-

Bi-?

Bi@-D

Bi@-0

Bi

Bi@-D

Hm-ABi-ABi@BiHm-DBi@-D

Hm-D

Hm-A

Bi-ABi@-A

Hm-DBi@-D

Bi®-D

Hm-D

Model'

IdeaIHIHiRelab

IH

PE

IH

B-DK2AAct!HA

CallGW

PE

Ca17

Ca14IH

B5270N

B-DK2A

\Range

Start

1.00.4

0.35

0.35

3.3

0.35

0.250.23VIS2.3

0.2

0.35

0.3

0.2VIS

0.21.6

2.1

0.35

End

-5.0-1.0

-2.6

1.2

-27

-5.0

-2.5-6.0

-22

2.5

2.5

2.2

2.5VIS

4.020

5.0

2.5

X Resolution<nm; visible)

0.21

1.6

10

3/30

<~1%

—1%v-1%

2cm"'

0.12

~1%

1

0.110

0.05-320.2-40

1/20

0.2-22

Xsampling(nm)

0.10.51

10

1

<«~1%

~1%

1

0.1~70

0.05-320.2-40

(FFT)

0.2-2.2

SampleOrientation'

VT-C

Hz-U

Hz-U

VT

Hz-U

V-CHz-UHz-UHz-U

Hz-UAny

Hz-C

Hz-U

Hz-UHz-U

Hz-U

Vt

V-C, Hz-U

EnvironmentControl4

LT, V

HT

LT, HT, V, G

LT, HT, V, G

LH, HT, V

LT.HT

HT

LTLT

LT, HT, V, G

LT, V, G

LT, HT, V, G

IrradiationFacility'

M

K, UV

UV

UV

K, UV, X

K, M

AnalyticalFacilities'

P. X

P, X

X, S

P,X,M,S,T,I,V

P,X,M

X,S

P.X.S.RA

P,X,S,D,F

X.S.SI

P,X,S

SpecialFeatures'

a

b,c

e

a.b

b.c

b

e

Upgrade*

In Progress

Repair

K

B.I

C,D,E

D

D

Planned

A.C.F

J

D.G

Bi, bidirection reflectance@, plus full angular controlHm, hemispheric (diffuse reflectance)D, digital outputA, analog output

IH, built in houseCa, GaryPE, Perkin ElmerB, BeckmanA, AnalectN, NickoletGW, Guided Wave

Hz, horizontalVt, verticalU, uncoveredC, cover glass used

LT, low temperatureHT, high temperatureV, vacuumG, gas mixing

K, keV ionsM, MeV ionsX, x-rayUV, ultravioletG, gamma ray

P, microprobeX, x-ray diffractionM, MossbauerS, SEMT, TEMF, x-ray flourescenceE, EscaA, AugerSI, SIMSI, instrumental neutron activation analysisV, vibrating sample magnetometer

a, same instrument as that on telescopesb, can precisely measure small samples (20-100 mg; 1 mm clasts)c, polarization opticsd, UV/visible flourescence spectral capabilitye, ion beam attached to environment chamber

A, spectral range extended to —5 f.B, spectral range extended to ultravioletC, environment chamber0, output digitizedE, optics for polarization measurementsF, camera to record state of sampleG, high pressure spectra (diamond cells)H, atmosphere control chamber1, increase spectral resolution to-^1/4%J, ultra-low (1.2 K) temperatures

K. small phase angles

ORIGINAU PAGE' ISOF POOR QUALITY

25

Table 7. Computer Facilities and Personnel Involved In Spectral Analysis

Location

University of Arizona

Brown University

Cornell University

University of Hawaii

Jet PropulsionLaboratory

Johnson SpaceCenter

University ofMassachusetts

University ofMaryland

MassachusettsInstitute ofTechnology

University ofPittsburgh

RensselaerPolytechnicInstitute

U.S. GeologicalSurvey (Denver)

U.S. GeologicalSurvey (Flagstaff)

University ofVirginia

WashingtonUniversity

University ofWashington

University ofWyoming

HardwareSpectraanalysis

Hp 9000

Micro Vax II

Vax(DEC) 750

Vax(DEC) 750

Vax(DEC)LSI

IBM pcVax(DEC)

Hewlett Packard

IBM pc

POP 11/73

IBM pc

IBM pc

Hp 9000Vax (DEC)

Symbolic

Cyber

Imageprocessing

Vicom

Vax(DEC) 750

Vax(Dec) 750

Vax(DEC) 750SUN 3/lls

Vax(DEC)

Gould

Pe 3240Vax (DEC)

Vax (DEC)Micro Vax II

Symbolic

OperatingSystem

VMS

UNIX/VMS

VMS/UNIX

MS-DOS/VMS

MS-DOS

MS-DOS

IBM-DOS

UNIX/VMS

VMS

VMS/UNIX

NOS

No. ofScientists

2

1

2

5

3

2

1

2

1

1

1

3

2

1

1

2

1

No. ofStudents

2

1

2

7

1

2

1

!

26

Chapter 6Future Applications and Requirements

IMissionsFuture planetary missions will rely heavily on spec-

tral reflectance and spectral imaging experiments. Be-cause of the immense data return expected from thesemissions in the next two decades, a new era will beginin qualitative and quantitative analysis of spectral reflec-tance data.

NASA has emphasized the major role reflectance spec-troscopy will play in the solar system exploration pro-gram by making the visible and infrared imagingspectrometer instrument (VIMS) a facility instrumentfor all missions starting with the Mars Observer. Majorsupport is required for the reflectance spectroscopy fieldin order to make the experiment results match theprominence in the payloads.

It appears that competing solar system explorationprograms in other countries will also include reflectancespectrometer experiments, further increasing the needfor an understanding of the techniques and science ofthe field.

The major missions likely to carry reflectance spec-troscopic investigations are listed here in approximatechronological order of data return.

Phobos - Soviet mission to Mars with emphasis onstudies of the satellite Phobos, will probably carryFrench infrared spectrometer similar to Vega instrumen-tation and multispectral CCD imaging. Launch, 1988;Mars data return, 1990.

Mars Observer Mission (MOM) — U.S. mission to or-bit and map Mars, will carry a visible and near infraredmapping spectrometer system. Launch, 1990; Mars datareturn, 1991.

Galileo — U.S. mission to Jupiter with extensive studiesof the planet and satellites, will carry multispectral CCDimaging and a near infrared imaging spectrometer(NIMS). Will probably fly by one or more asteroids inaddition to Jupiter mission. Launch, 1989; data returnat Jupiter, 1994; asteroid data return, 1990 (?) and,1992 (?).

Soviet Lunar Polar Orbiter — Soviet lunar mission withinfrared spectral reflectance capability. Launch, early1991 (?); data return 1992 (?)

Lunar Geosciences Observer — U.S. lunar mission,similar to MOM .'Launch, early 1992 (?); data return,1992 (?).

Vesta — Soviet/French mission to Mars with separatespacecraft going to one or more asteroids; will proba-bly carry infrared spectrometers on both Mars andasteriod 1994 (?).

Comet Rendezvous/Asteroid Flyby (CRAF) — U.S. mis-sion to an asteroid and comet nucleus, will carry a visi-ble and near infrared reflectance spectrometer withmapping capability. Launch, 1992 (?); arrival at comet,mid-1990s.

Cassini — U.S./ESA mission to Saturn and Titan, willorbit and study rings and satellites as well as Saturnand Titan. Cassini will probably also fly by an asteroiden route. Recommended pay load includes visible andnear infrared spectral mapping experiments on the or-biter and some near infrared spectral and/or imagingsystem on the Titan probe. Launch, mid-1990s (?); ar-rival at Saturn, ~ 2002 (?).

IMajor Scientific Issues and QuestionsAnalysis of the current planetary reflectance spec-

troscopy data sets (which are almost totally telescopic),plans for future telescopic work, and preparation forthe upcoming spacecraft experiments point to a num-ber of major scientific problem areas that are the fo-cus of much of the current work in the field. Thefollowing sections indicate current broad researchtrends.

Icy surfaces/frozen volatilesOne major new area of investigation made possible

by recent advances in spectroscopic instrumentation andtheory is the search for volatiles such as NH3, CH4, andCO on the surfaces of icy satellites. Because most of thesevolatiles, if they occur on satellite surfaces, probably existin small quantities and in clathrate or hydrate form, therequired data and spectral analysis capabilities have notexisted until recently. This is an important new area ofspectral investigation because the results are necessaryfor understanding the conditions of satellite formationand the important drivers for their subsequent geophysi-cal, geochemical, and geological evolution. At the tem-peratures of most of the satellites, normal H2O ice isa reasonably strong rock, and the observed geologicalactivity on many icy bodies is probably facilitated bythe presence of these non-water condensables.

27

Dark material in the solar systemLow albedo material (p/^3-10%) is a major compo-

nent of many bodies in the solar system. The surfacesof Mercury and the Moon are composed basically ofsilicates which are intrinsically relatively dark and arefurther darkened by soil maturation processes. The darkmaterials on the satellites of Mars, many asteroids, out-er plant satellites, some planetary rings, and cometnuclei have very different spectral properties from thelunar soils and are believed to be carbonaceous in na-ture. The relationship of this material to the dark car-bonaceous meteorites, the differences among the severaltypes of dark objects known, and the origin of this ma-terial (whether primordial or produced by irradiationof carbon-rich ices or some combination of both) areopen questions and are or should be the subject of in-tensive study using spectral techniques.

Asteroidal materialsOf the eight missions listed above, five may obtain

spectral data for asteroids. These missions will be thefirst to these very important objects. Asteroids providea window on the early processes of condensation andaccretion which are obscured by later events onplanetary-sized bodies. Major gaps remain in our abili-ty to interpret the data expected from these missions.

Reflectance spectroscopy results from telescopicstudies suggest that a major fraction of inner-beltasteroids are metal-rich objects (perhaps analogous tothe pallasite and lodranite meteorites). Chondriticasteroids would also have a metal component in theirregolith, but derived from discrete gains in the bedrockrather than from the fracture of large metal masses.Laboratory spectra of these meteorites have not beenobtained yet because of the extreme difficulty in produc-ing a realistic metal-rich regolith simulation from solidmeteoritic NeFe alloy. There is little information abouthow impact gardening affects a material whose com-ponents have radically different mechanical properties,since the terrestrial planet surfaces do not have any suchmaterials. Tt> properly interpret spectra of asteroid areasreturned by these missions, a detailed knowledge of thephysical nature and spectral properties of metal-silicateregoliths (derived from both chondritic and differen-tiated substrates) is needed. Such knowledge will requirean integrated study of mechanical properties, measure-ments, impact simulation experiments, regolith garden-ing models, and spectral measurements to derivecalibrations of metal/silicate ratios for use in analysis ofspacecraft data.

Mars mafic mineralogy and interiorcomposition

The mineralogy of the volcanic flows and other fea-tures on Mars is a good indicator of the thermodynamicand chemical conditions under which these features andtheir composite material formed. Since they are der-

ived from the Mars interior and at different times inthe evolution of the planet, they are a useful probe intothe evolution processes. A quick study of Mars surfacemorphology using images shows many volcanic features,including large shield volcanos and extensive flows fromdifferent eras. Volcanism played a major role in the evo-lution of Mars. Existing Mars reflectance spectra showthe presence of pyroxene and possibly olivine as wellas the weather products (amorphous iron oxide) of vol-canic glass. Just recently, telescopic instrumentation hasbegun to resolve spatially, with high signal to noise andbroad spectral coverage, the major volcanos and volcanicregional units on Mars. Future Mars-Earth oppositionsshould enable us to increase our knowledge of themineralogy of these units. This knowledge, with esti-mates of the time sequence of feature implacement,should help constrain models of the interior evolutionof Mars.

Salts on Mars and volatile evolutionExtensive evidence of catastrophic surface flooding

on Mars, indicating huge aquifers, together with evi-dence for extensive hard frozen permafrost which couldbe intruded by igneous bodies, suggests the possibilityof brine development and stabilization during Mars' his-tory. There is also direct Viking-observed evidence forsalt cementation (the soil-capping "duricrust") at the land-ing sites which may be even better developed elsewhereon Mars. Finally, many models suggest an early CO2greenhouse which would require subsequent formationof large carbonate deposits to "hide" the CO2 in theregolith. Thus the search for salts is of primary interestfor the MO mission. The best hope is to identify promi-nent infrared absorptions for the anion groups in sul-fates, carbonates, and nitrates in the 3—5 p range andsecondary bands at shorter wavelengths. However, ex-tensive laboratory work is needed in which spectra to4.5—5.0 n are measured of trace or minor amounts ofthese infrared-active salts mixed with likely matrix ma-terial (like palagonite) thought to constitute the bulk ofthe regolith. Such work has not yet been performedbut the results would be highly supportive of one ofthe major Mars Observer Mission goals.

Lunar basins and early crustaldevelopment

The major impact basins on the lunar surface haveexcavated material from a variety of depths and deposit-ed this material in a systematic manner around the im-pact site. Analysis and interpretation of spectra obtainedfrom these deposits provide key information concern-ing the composition and stratigraphy of the lunar crustin the pre-impact target sites. Comparison of the resultsfor different basins will lead to a better understandingof lateral variations in crustal composition. Spectral datafor distal basin deposits can be used to determine theimportance of "local mixing" by secondary cratering

28

processes and to help place the returned lunar samplesin their proper regional context.

Sulfur and sodium chemistry andmineralogy on lo and Europa, andmagnetospheric effects on the Galileansatellites

Sulfur and sulfur compounds are thought to be ubi-quitous in the inner jovian satellite system. These materi-als, which are produced on lo, are spread throughoutthe jovian system by the powerful jovian magnetosphere.In the most general sense, the major issues that spec-tral reflectance properties can address include: (1) whatis the nature of the spectrally active materials on thesurface of lo? (2) what relationship does this materialhave to the crust of lo? (3) how are these materialsformed? and (4) what effects do these materials, oncecaptured into the jovian magnetosphere, have on thespectral reflectance properties of the other jovian satel-lites (namely, Europa and Amalthea)?

Spectral reflectance properties of these satellites havebeen investigated on both global (ground-based telescop-ic and Voyager 1 and 2) and regional (Voyager 1 and2) scales. Data exist for studies on local scales, but littlehas been done. Laboratory spectral reflectance proper-ties of sulfur and sulfur-related compounds are requiredif the issue of sulfur versus silicate (basalt) landformson lo is to be addressed correctly. Similarly, laboratorystudies of materials in simulated jovian environments(i.e., radiation, thermal cycling, etc.) must be attemptedbefore we understand what happens on local andmicroscopic scales to form and modify the surfaces oflo, Europa, and Amalthea. Ion implantation into ice andsilicate materials is a relatively unexplored area in thecontext of spectral reflectance measurements. Thesestudies will have particular relevance to Europa, Gany-mede, and Amalthea.

ISurface ModificationA major problem for geologists trying to understand

the surface composition of solar system objects has beenthe various surface alteration processes. These are of-ten interesting in themselves. Also, knowledge ofprocessing (weathering) rates for surface materials cangive information on the age of soil and rate of turn-overof crustal materials. A simple example is the amorphouslayer produced on lunar materials exposed to solar windbombardment which indicated that a particular mate-rial in an Apollo sample was indeed on the surface (i.e.,weathered) at some time. Of course, knowledge of thevery active weathering rates on Earth is an importantgeologic tool. The weathering processes also indicatemuch about the environment experienced now and inthe past.

Weathering can also play a role in obscuring the pri-

I

mary mineral composition of the surface. There aremany interesting and important problems in this area,for example, hydroxalization and oxidation of Mars sur-face materials. The effects of weathering vary; someplanetary bodies have (had) atmospheric and fluid enve-lopes, and some are rock with essentially no atmosphere,such as the Moon, Mercury, and the asteroids. Thesemay be modified by meteoritic, solar, and galactic par-ticle bombardment and possibly by ultraviolet irradia-tion. In fact, the recent evidence for sodium sputteringon Mercury may help increase our understanding ofthat surface.

The surfaces of the small bodies and grains in the out-er solar system, particularly those orbiting within mag-netospheres, have been irradiated at a variety of levelsearly in their formation and are being irradiated at pres-ent. Because these surfaces are composed of volatilematerials, the irradiation effects are correspondinglymuch more dramatic than those produced in the rockyobjects in the inner solar system. For example, con-densed volatile materials can be directly converted toorganic materials and organics to highly carbonized(dark) materials by particle radiation. In addition, par-ticle radiation has been shown to compete with subli-mation in determining the grain sizes of the icy regolithsof outer solar system bodies and clearly competes indetermining the crystallinity of the volatile layer. As thepenetration depths of the incident radiation are oftencomparable to the sampling depths of the reflected pho-tons, the effects of such weathering will be evident inthe wavelength region of interest. Therefore, reflectancespectra can give information on the active weatheringof these surfaces as well as on the important questionof whether or not the obscured materials areprimordial.

Planet Surface Mineralogyand Processes

Determination of the mineralogies of altered and un-altered primary rocks and how they vary across aplanet's surface is a major goal of reflectance spectrosco-py. Indeed, the technique is the only one available forglobally mapping mineralogy. All the terrestrial planetsappear to have undergone differentiation into crust,mantle, and core. Primary rock mineralogy provides di-rect clues to the composition of these basic global com-ponents and the nature of their implacement. We knowthat Earth has a granodioritic crust and that the Moonhas an anorthositic crust. The compositions of the mer-curian and martian crusts are unknown, but they canbe determined from the mineralogies of rocks of thecratered unplands or of crustally derived volcanic rocks.Of particular interest for models of accretion of Marsis the extent to which hydrated minerals such as am-phiboles and micas are present. Similarly, the mineral-

29

ogy of volcanic rocks provides direct clues about suchfundamental mantle properties as oxidation state, Fe/Mgratio, and Ti content. In addition, layering in the uppermantle can be inferred from the different mineralogiesof differently aged rocks, as determined by crater-counting studies.

Knowledge of the variability of volcanic mineralogywil lead directly to a better understanding of volcanicprocesses. Reflectance spectroscopy may, for example,reveal that different volcanic landforms, such as shieldvolcanos, paterae and lava plains, and volcanic provincessuch as Tharsis and Elysium, are compositionally dis-tinct. Most volcanism on planets other than Earth ap-pears to be basaltic. A wide variety of products thatresult from interaction of lava and groundwater orground ice may be present where more siliceous formsof volcanism dominate.

We must achieve a better understanding of the miner-alogy of primary and secondary (weathered) alterationproducts on Mars. Abundant chemically alteredweathered products appear to be present, but it is notclear when and under what climatic or environmentalconditions these products were produced. Knowledgeof the mineralogy of the weathered products, as provid-ed by spectroscopy, will greatly help us understand theseproblems. Detection of salts such as sulfates, carbonates,and nitrates will also help us understand not only thesource of the weathered debris and the sink for vola-tiles but also the climatic conditions under which trans-port and segregation of the products took place.

Scientific questions concerning the Moon andasteroids that will be addressed by reflectance spec-troscopy are more sophisticated because of the availa-bility of samples which can be studied in the laboratoryand used to model components of an unexplored sur-face. Reflectance spectroscopy is particulary effectivehere because the lunar and meteorite samples providecompositional information that ties the remote meas-urements with reality in a very direct way (\e., ground-truth), and it provides not only scientific results but alsotechnique verification and development.

It seems likely that new assemblages and new com-ponents will be discovered with spacecraft measure-ments of the Moon and asteroids. For example, a varietyof pristine crustal materials have been identified as frag-ments in the lunar sample collection; their lateral andvertical distribution is unknown, but fundamental ques-tions about the formation and evolution of the lunarcrust depend on this information. For the Moon, thehigh spatial resolution spectra expected from an orbit-ing satellite will allow extensive details of crustal stratig-raphy to be examined locally (largely throughmeasurements of the material excavated by large andsmall impact craters) and globally (through measure-ments associated with a variety of major basins). Pri-mary requirements to obtain the desired scientificinformation from such studies include developing a

detailed understanding of the spectral character of keylunar materials and the effects of shock metamorphismand brecciation as well as the deconvolution of com-plex multicomponent lunar spectra to produce accurate^measurements of mineral abundances.

Asteroid science has similar requirements (laborato-ry mesurements of key meteorite materials, examina-tion of alteration effects, and accurate analyticaltechniques). The questions are, of course, quite differ-ent and relate to distinguishing the nature and extentof the earliest differentiation events in the solar system.A major question is whether some asteroids are extinctcomets or whether cometary nuclei are like asteroids.Visible and infrared spectroscopy will be a primary toolin addressing this question with future Earth-based andspacecraft observations (e.g., GRAF).

For Mercury, a major question is whether there is anyferrous iron at the surface, and if so, in what miner-al(s). If not, is the surface highly reduced? The sodiumdetected in the atmosphere presumably is sputteredfrom the surface, implying the presence of an Na-bearing mineral in the regolith. This presents a puzzlebecause Mercury is thought to have formed under high

, temperature conditions that would not have been favora-ble for retention of large amounts of sodium.

Near-Earth asteroids are particularly interestingbecause they are near Earth and may account for a largeshare of the meteorites. Some investigators believe thatthese objects contain a population of extinct cometnuclei. Others argue from existing spectral reflectancedata that all these objects can be explained by mineralassemblages like the main belt asteroids and that theyare derived from that source, expecially near the 3:5resonance. Continued telescopic observations and a low-cost spacecraft rendezvous will determine morecompletely the suite of mineral assemblages composingthis group of objects and answer the question of theirultimate origin.

Outer planet satellites pose other challenges. Icy bodiespresent water ice and clathrate mineralogies which mustbe identified. Water volcanism or other resurfacingprocesses are possible. lo is a most active volcanicenvironment, with flows, plumes, and calderas, but eventhe major type of volcanism (silicate, sulfur) and theeffects of the vacuum environment on materialproperties are not well described. The Galileo NIMSinvestigation and further ground-based observations willpresent important data sets for interpretation.

ITechniques and Data RequiredIn order to address the scientific questions described

above and to prepare for the analysis of spacecraft datain the near future, considerable effort in a number ofareas is required. Again, this discussion is meant to beillustrative and not exhaustive.

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Theoretical workThe physical and chemical principles and the general

basis for understanding and interpreting reflectionspectra have been brought to a reasonably mature levelin the last two decades. The effort can be thought ofas having three components: (1) identifying the presenceof specific minerals, (2) making quantitive estimates ofphase chemistry, and (3) determining the relativeabundance of the phases. The latter two are moredifficult and require better models. The effort requiredin these areas includes work aimed at understandingthe effects of temperature and the physical state of thesurface on spectrophotometric properties.

Underlying the application of reflectancespectroscopic data in planetary sciences is the correctassignment of observed spectral features. This isachieved in large measure by direct measurements inthe laboratory of candidate minerals and mineralassemblages (rock types) believed to comprise materialson weathered or irradiated planetary surfaces. However,the ultimate assignment of band energies and intensitiesis based on calculated energy levels and transitionprobabilities. As molecular orbital calculations (requiringhuge computing capabilities) become more sophisticated,necessitating considerations of next-nearest neighborand other environmental interactions (variable ligands,point defects, broken bonds at crystal surfaces), so toowill the precision of interpreting reflectance spectraevolve. The special properties that planetary materialshave provided (Fe and Ti in lunar glasses, Ti3+ and Fe2*—-Ti4+ spectral features in lunar minerals, poorlycrystalline martian Fe3+ oxides and clay silicates) haveyielded problems unique to planetary science. Suchleading-edge fundamental scientific research mustcontinue to be carried out.

Particularly important are mathematical modelsrelating fundamental material properties (such as thecomplex index of refraction) to the diffuse reflectionspectrum of a realistic planetary surface composed ofsuch materials. This allows measurements of spectra ofend members of material compositions and mixturesin the laboratory to be used to calculate spectra of amultitude of mixtures and gradations of these materialsand reduces the need for more expensive and time-consuming laboratory measurements. This is acomplicated problem because of the multiscatteringenvironment among grains of differing size, shape, andoptical properties. A particular problem is the case ofmineral mixtures and the methods for deconvolving themixture spectra. Models exist, but they must be mademore sophisticated and easier to use.

Several specific requirements can be identified in thisarea:

Continue to develop a mathematical model forcalculating the diffuse bi-reflectancespectrum for mixtures of materials using theoptical constants of end members.

Continue to provide the association of specificbands with the chemical nature of thematerials.Continue to develop models for deconvolvingthe spectrum of mixtures of materials andderive the end member materials and theirrelative contributions.Develop models for separating theatmosphere from the ground for Marsobservations.

Telescopic observations (gound based andEarth orbital)

Essentially all data obtained for solar system objectshave come from ground-based telescopic observations.While more and more data will come from the missionsdescribed in the beginning of this section, telescopicstudies will remain a critical element of planetaryreflectance spectroscopy for a number of reasons:

Some bodies, particularly in the outer solarsystem, will not be visited by planetarymissions until well into the next century.Telescopic studies will be used to supplementand support missions, providing time andspectral coverage unavailable to thespacecraft experiment and/or data bases onother similar objects to provide the contextfor spacecraft measurements (e.g., forasteroids and comets).Telescopic observations (and Earthobservations) will remain the proving groundfor new instrumentation and techniques,since spacecraft experiments must by natureuse tried and (by the time of encounter)usually out-of-date methods.

Future requirements to maintain and advance theknowledge and technique base in reflectancespectroscopy as applied to planetary science include:

Support the ground-based telescope facilitiesrequired for the measurements. The mostactively used facilities include the NASA IRTFand the University of Hawaii 2.2 m telescopeson Mauna Kea. The JPL Table Mountainobservatory, McDonald Observatory, and KittPeak telescopes have been used as well. Thecurrent pressure for observing time isillustrated by the fact that observing time onthe IRTF is oversubscribed by a factor of 3for the current observing period (fall 1986)Support the modification of existing and thedevelopment of new array spectrometers toreach fainter objects, obtain better precisionover a wider spectral range, particularly inthe 1.0 — 5.0 /* spectral region, and produce

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data sets which simulate those to be obtainedby space missions.Provide better support in general for facilitymaintenance and provide better support forguest investigators to use existing equipmentand telescopes.Provide for the restoration to a commonformat of the existing data sets; they aredifficult or impossible to duplicate. These datasets should be placed in the Planetary DataSystem as part of the reflectancespectroscopy node responsibilities.

A problem in this area is that the ground-basedobserving program is supported by a separate programwithin the Solar System Exploration Division other thanthe Planetary Geology and Geophysics Program. Closercoordination is required between these two programs.

Laboratory measurementsLaboratory measurements have increased in the past

5 years as several new research centers have developed.This is in response to the greater demand for such data.The existing data sets, especially the earlier sets, are notwell documented and have not been restored to acommon format. Some are on tapes that are difficultto read. This kind of information will be in demand inthe future.

Continued laboratory work aimed at addressing someof the problems discussed above is required to providea sound interpretive base for both mission and telescopicwork. This work should focus on obtaining a detailedunderstanding of the physical and chemical processesthat affect spectral information in the environment ofactual planetary surfaces; these environments differgreatly from object to object. The development ofappropriate and well-characterized data bases ofspectroscopic information is a part of this effort, butthis should not consist of simply building large referencelibraries of spectra. It is equally important to obtain anaccurate analytical capability to extract the desiredinformation from complex multicomponent spectra.Among the requirements are

Environmentally controlled studies ofcandidate planetary volatiles

More information about the mid-infraredrange, from 2.5 to 50 /*

Studies aimed at unraveling various formsof spectral mixing

Studies of the effects of sampletemperature on spectra

Environmentally controlled studies of saltsand hydrated minerals, including duringhydration and dehyration

Radiation bombardment of particulatemedia rather than smooth, flat surfaces, andparticularly of ices, so that processes in aregolith are simulated realistically

Studies of optical properties of crystallinephases having sub x-ray dimensions

Better characterization (chemical, phase,grain size, etc.) of samples upon whichspectral measurements are made

Imaging spectroscopyOne of the most important trends in the field of

remote sensing is the development of spectral imagingsystems which produce large, two-dimensional arraysof moderate to high resolution spectra—images'—forwhich each picture element is associated with a fullspectrum, not just a few broadband colors. These datasets are often called image cubes. Virtually all U.S.planetary missions in the future will carry devices ofthis sort, and a number of Earth-orbital spectral imagingexperiments will have been flown (indeed, terrestrialapplications are providing one of the strongest driversfor the development of these techniques).

These developments will have a profound effect onthe field of reflectance spectroscopy and pose a numberof formidable challenges to researchers. As the fieldmoves from the "classical" mode of single spectrumanalysis to manipulation of massive (> 10^8 to 10lv" bits)data sets, new methods will have to be developed forpreparing, assimilating, and analyzing these data. Thescale of this problem may be illustrated by consideringthat there are now perhaps about 1000 visible to nearinfrared spectra of individual planetary bodies (mostlyfor lunar areas and individual asteroids) or differentparts of their surfaces; the Galileo NIMS experiment willexceed this data volume in its first 25 minutes ofoperation! One major challenge is simply preparing thespacecraft data set in a form which is useful for furtherdetailed analysis; the experiments will not in generalproduce simple, error-free, geometrically pure databases, and the production of geometrically accurate,well-sampled data bases with spacecraft and lightinggeometry effects removed will be a major task. Learningto organize and extract the geochemically andgeologically most useful information from these databases will require a major research effort as well,combining mathematical tools for data handling,laboratory and theoretical analysis, and correlations withother data sets.

Work is currently being carried out in many of theareas mentioned above, but far more must be done toprepare for the data expected in the next 10 years. Inthe very near future, workers in remote sensing willdeal with increasingly unified mixtures of spatial andspectral information and will often be presented with

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spectra in an imaging context and images as collections Develop innovative approaches for analyzingof spectra. Some suggested areas of emphasis are image cube data sets using expert systems

Continue to develop and distribute integrated and artificial intelligence technology to extendsoftware data processing systems such as the scientists' capability.GARP and SPAM for the routine handling of Promote research projects which will test andimage cube data sets in coordination with motivate these capabilities.space mission projects such as Galileo andMOM, for which such development is alsoneeded.

Chapter 7Strategy and Implementation

IScope of Program and ApproachThe scope of the reflectance spectroscopy program

is extremely broad. The program encompasses allobjects in the solar system and involves many disciplinesother than spectroscopy, such as geology, geochemistry,geophysics, and atmospheric science. The nature of theprogram is documented in previous chapters. Here weemphasize that a broad scope of effort requires a carefulbalance among several areas of research in order to beeffective. These include:

Theory and technique of reflectancespectroscopyLaboratory studies of candidate materialsAnalysis and interpretation of existingplanetary dataAcquisition of new* telescopic dataPlanning and preparation for spacecraftmissionsParticipation in missions and in post-missiondata analysis and interpretation

These areas of research are so closely interwoven thatthe strength of the program depends on maintaininga balanced effort that covers all areas. For example,further development of background theory is ofparamount importance at this time in preparation forupcoming spacecraft missions which will requireentirely new methods of spectral analysis. In addition,new telescopic data will not only produce important newdiscoveries, but will be an important high-spectralresolution supplement to future spacecraft data from,for example, Galileo NIMS.

Any implementation of the program must take intoaccount the problem of establishing a long-termperspective and a continuity of effort. Future NASA andforeign spacecraft missions are primarily orientedtoward remote sensing experiments (in contrast tolanded experiments or sample return), and reflectancespectroscopy is an essential part of most payloads. Inan era of budget awareness and post-Challengerrescheduling, the missions that once appeared imminentare now likely to be postponed. It will be a majorchallenge to maintain and develop an innovative andforward-looking program in an era of mission delaysand uncertainty. However, without this continuity thehard-won missions may be compromised by lack of

preparation, reducing the potential for reflectancespectroscopy to play a key role in future planetaryscience discoveries.

IProgram FocusCertain aspects of the reflectance spectroscopy

program urgently require attention if mission objectivesand science objectives are to be met. These includecritical research problems and other problems that arelargely programmatic in nature. More detaileddiscussions of some of these problems and proposedsolutions appear in later sections of this chapter.

Mission ReadinessPlanetary reflectance spectroscopy has its roots in

telescopic observations. Telescopic spectra are not easilyobtained because of object availability, telescopeavailability, observing conditions, etc. Even today, high-quality telescopic spectra of planetary objects arenumbered in the hundreds. Interpreters have been ableto treat spectra on an individual basis and have not hadto be concerned with processing large quantities of data.

During the rapid evolution of reflectance spectroscopyover the last 20 years, virtually no spacecraft missionshave obtained high-resolution spectra of planetarysurfaces. (An exception is the Mariner 6 and 7 IRSexperiment in the 1.9—6,0 /x region.) Meanwhile thetechnology in detectors and in data storage andtransmission has surged ahead to the point at whichfuture missions can produce an unprecedented floodof spectroscopic data. Furthermore, the data can be filedand displayed as images. A few tens of seconds oftransmission from Galileo NIMS can exceed the total ofall of the existing telescopic spectra of the jovian system.

The bulk of future reflectance spectroscopy data fromspacecraft cannot be efficiently examined spectrum byspectrum as in the past. An entirely new approach isnecessary, one based on a scientific rationale and usingnew high-speed data processing techniques. Newapproaches are now being tested in a few laboratories.However, one of our key findings is that there presentlyexists an appalling mismatch between the objectives ofNASA (and foreign) planetary missions to conduct highdata rate reflectance spectroscopy experiments and thepresent capabilities for data analysis and interpretation.

We identify below three critical research areas thatrequire immediate attention.

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Large data sets and the merging of spectral andimage analysis. A crucial aspect of the presentmismatch between mission objectives and currentcapabilities is the problem of managing large data ratesfrom reflectance spectroscopy experiments onspacecraft. This is partly an engineering probleminvolving data links, data storage, data compression, etc.It is partly a problem at the stage of interpretation, forthe scientific community has little experience in workingwith large data bases; the necessary tools and strategieshave not been developed. It is widely agreed that theproblem will not be solved by simply increasingcomputer throughput. It is more likely that the modelingstrategies (discussed below) will be used to selectivelyprobe the database, guided by scientific questions.

The appearance of imaging spectrometers has foreverchanged the nature and scope of reflectancespectroscopy. Future missions will obtain spectroscopicdata in the form of image arrays. Multiband images willbe treated as spectroscopic arrays. Photogeology andreflectance spectroscopy will converge to provideinterpretations that connect compositional informationwith landforms. Rapid strides are being made in thisdirection in the NASA terrestrial program using newAirborne Imaging Spectrometer (AIS) data beinggathered by JPL.

Images are by nature large data arrays. As the spectraldimension is increased to the range of 100 or morebandpasses, which are necessary for spectroscopicinterpretations, the problem of data managementbecomes acute, as discussed above. It is still common,however, for scientists and program managers to treatspectroscopy and image analysis separately. This divisionis based on imaging in a few broad bandpasses in pastplanetary missions and terrestrial Landsat missions.With the advent of imaging spectrometers, the approachto data management must evolve beyond our image-processing techniques. Current standard methods, suchas making ratio images and color ratio composites, areof limited use in dealing with hundreds of bandpasses.Although a few research groups are addressing theseproblems, the level of effort within the planetaryreflectance spectroscopy program is low and in fact isdeclining.

Enabling instrumentation. Two areas requireprogrammatic attention. First, existing laboratory andtelescope observing facilities must survive if the missiongoals discussed above are to be achieved. Funding mustbe maintained at a level that allows existingspectrometers and other equipment to operate. Fundingfor technical personnel is the highest priority in mostlaboratories, followed by support for maintenance andrepair of facilities.

Second, scientific progress depends on new specializedfacilities: (1) laboratory equipment to allow spectroscopic

measurements of frozen volatiles under conditions suchthat samples can be characterized by x-ray diffractionand other techniques, and (2) new telescopicinstrumentation to allow a 10 to 100-fold increase insensitivity of spectra of faint objects in the solar systemand for small areas on Mars. New facilities such as thesemight best be run as cooperative efforts.

Predictive spectral modeling. Laboratory referencespectra and reflectance theory together provide thefoundation for the interpretation of telescopic andspacecraft reflectance measurements. Advances in bothareas within the past 5 years have opened the possibilityof accurate prediction of how a spectrum will respondif the measured material is modified in terms of particlesize, mixtures with other materials, and changes inlighting geometry. A further objective is the ability tomodel the spectral effects of atmospheric attenuationand scattering and of instrumental attenuations.

The inverse, the ability to deduce the variouscomponents and their condition on a planetary surfacefrom a known spectrum and lighting conditions, is theprime operational objective. It is entirely unrealistic totry to develop a library of reference laboratory spectracovering all possible materials, particle sizes, and possiblemixtures. Instead, by measuring the spectra of arelatively few materials under known conditions, otherspectra can be calculated using tested algorithms. Thedifficulty is to make this technique work in reverse: givena photometric-quality spectrum and the lightinggeometry, determine the mineral composition andphysical state of the surface. The goal of all reflectancespectroscopy and of this approach specifically is theability to quantitatively determine the phase abundancesand physical states of remotely measured materials.

The goal of predictive spectral modeling is realisticin the view of some investigators familiar with recentdevelopments in the field; however, the present level ofeffort in the program is very modest, partly becausetechnique development is not a high priority of proposalscience review committees. Yet an approach like this maywell be the only way to analyze efficiently the largequantities of data expected from new missions.

Vulnerability of a Leveraged ProgramAttempts to maintain a balanced program with a

broad scope in the face of mission delays and constraintson the research budget appear to have resulted in aprogressive reduction of support for most indiviudalinvestigators over the past 5 years, even though newinvestigators were added and the proportion of thePlanetary Geology Program funding for this field wasmodestly increased. At the same time, the scientific andtechnical sophistication of the field has increased,

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thereby increasing the requirements for laboratoryfacilities, computational facilities, telescopicinstrumentation, etc. The program is now highlyleveraged, that is, high research output is possible onlybecause other NASA programs, other governmentagencies, and universities are carrying many of the realcosts of planetary reflectance spectroscopy research.

As a simple example of leveraging, consider theinvestigator whose funding has diminished by somefraction for each of the last 5 years. Five years ago theplanetary progam supported a proportionate share ofthe expenses of running the investigator's laboratory,including technician's salaries, maintenance and repairof equipment, and other costs. As the annual budgetdiminished, the investigator, reluctant to reduce his orher output in a competitive environment, tried to shiftthe real costs of operating the facilities to other areas.Another grant that relies on use of a spectrophotometernow supports all of the operational costs. A privatefoundation and university matching funds are used topurchase a new computer or to replace failed orobsolete equipment.

In the short term, shifting costs to other programsor insititutions appears to be desirable because it resultsin more research per dollar for the reflectancespectroscopy program. This leverage, however, worksboth ways, because the control of the program passesto others who do not necessarily share the objectivesof the reflectance spectroscopy program. If the otherprograms default or change direction, the reflectancespectroscopy program is vulnerable.

At present, the reflectance spectroscopy program ishighly leveraged in terms of the support of laboratoryand observational facilities. Most investigators who doexperimental work rely on other sources of support.With further constriction of the progam, we wouldexpect that at some point the demands of the otherprograms will eclipse planetary reflectance spectroscpywork, and the objectives of a broad and balancedprogram will be compromised.

ISchedule of the ProgramThe reflectance spectroscopy community recognizes

that spacecraft missions are the major drivers forresearch funding. Tb a large extent, the present dilemmaof shrinking resources is linked to the absence ofmissions returning or about to return spectral data.Following the Challenger tragedy and the postponementof Galileo, the NASA schedule is uncertain. Severalforeign misisons are planned in the next few years (seechapter 6); however, the extent of U.S. participation willprobably be minor, and support for the reflectancespectroscopy program is not a consideration. The onlycertainty at this time is that reflectance spectroscopy

experiments will eventually fly on Galileo, MarsObserver, and other NASA missions.

Because funding is linked to missions, the slippingmission schedule poses an immediate and serious threatto the scope, balance, and quality of the overall researchprogram. In addition, the mission budgets, especiallyfor data handling and analysis, are decreasing. The MarsObserver VIMS budget for measurement planning anddata processing, for example, is a factor of 3 to 5 toolow, especially in light of the slip in the Galileo Project.In similar situations the basic resarch budget has beentapped to supplement the shortfall, further destabilizingthe program.

As discussed above, the program is leveraged, and isat or below the critical mass necessary to meet theobjectives of future missions in both direct support andin providing a science and technology base. Thus themain issue regarding the schedule of the program ishow long the present effort can survive.

IPersonnel and FacilitiesPersonnel

The scope of the reflectance spectroscopy programis determined by resources for both personnel andfacilities; however, the larger share of the cost is forpersonnel. The size and nature of the sciencecommunity are outlined in chapter 5, tables 4-7. Thecommunity covers a broad science area in terms ofdiscipline (geology, mineral physics, spectroscopy,astronomy, atmospheric science, etc.) and is highlyvaried in specialty (Mars, moon, asteroids, icy satellites,lo, etc.). Most scientists work across traditional disciplineboundaries; while all have become knowledgeable inspectroscopy, few are spectroscopists by formal training.In general, the community is composed of planetaryscientists who have become involved in the use anddevelopment of reflectance spectroscopy as a powerfulnew analytical tool.

Specialization has developed as the field has matured.There are a few (perhaps one to three) specialists in eacharea, such as asteroid mineralogy, icy satellites,reflectance theory, lunar rocks, mineral spectroscopy,the martian surface, etc. While there is a broad scopeof understanding among the small group of investigators,specialization has progressed to the point at whichpersonnel are not readily interchangeable.Programmatically, this means that if an investigatorleaves (e.g., for lack of funding), it is likely that a keyspecialty will be lost. In certain areas the loss of evena single investigator would be a major setback to theprogram in terms of mission readiness.

It is more difficult, within the scope of this report,to judge the quality of the program. This is best donefrom a broader perspective in planetary science on thebasis of the contributions of reflectance spectroscopy

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to our understanding of the solar system. It is knownthat the personnel in the program compete forresources through peer review of proposals by aninterdisciplinary panel of planetary scientists, wherepublished results are continually assessed. Unproductiveresearchers in this or any other area probably do notsurvive long in this environment, especially after severalyears of tight budgets. We believe that furtherreductions in numbers of investigators will result inreductions of high-quality science.

A deliberate effort has been made to bring a few newinvestigators into the program, even though the overallbudget has offered little opportunity for growth andchange. Shrinking programs are especially difficult foryoung investigators to enter: they have not had theopportunity to produce extensive research results, andthey must compete with established scientists. Whilethis problem is found in many other science areas, thereis a unique and important difference in the case of thereflectance spectroscopy program. With the schedulefor NASA planetary missions extending into the nextcentury, and with the existing commitment to flyreflectance spectrocopy experiments on all or most ofthose missions, young scientists must be trained nowand supported after they graduate to provide thenecessary long-term continuity. Given the major technicalchallenges discussed above, we cannot skip a generationor two of graduate students and then call on future newgraduates to meet the unfolding mission challenges.

FacilitiesThe facilities in use in the NASA solar system studies

reflectance spectroscopy effort are listed in chapter 4,tables 4-7. As discussed above, these facilities were onlypartly purchased with funds from this NASA programand are only partly operated and maintained by yearlyfunding from the program. There is a wide range ofadequacy in the various laboratories. There are one ortwo well-equipped and up to date U.S. laboratoriescapable of measuring the spectra of samples undercontrolled conditions, although none is capable ofhandling frozen volatiles adequately. Most facilitiesoperate below potential because of outdated equipmentand/or lack of funds for operating personnel and formaintenance and repair.

Laboratories equipped for studies of samples andtelescopic measurements are generally also used byoutside investigators. Some scientists in the program relyentirely on the facilities of others. This cooperativeapproach is desirable and conservative of resources;however, NASA has not consistently maintained orincreased operations funding for the institutions thatin effect serve as program facilities.

Computer facilities differ widely in nature andadequacy throughout the program. In general, theprogram has not been able to purchase computers forinvestigators, and other programs or institutions have

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borne these costs. To date, most of the research in theprogram has not been computation-intensive. This isnow changing rapidly, as spectral analysis increasinglyinvolves image cube processing. Few investigators haveimage cube processing facilities, which are costly andrequire additional personnel for operation anddevelopment. In the present budget climate it is desirableto concentrate limited resources for image cubeprocessing in a few laboratories. In the long term,hardware costs may decrease enough to allow widedistribution of imaging cube processing facilities;however, the costs of personnel for operations,maintenance, and software development will probablynot diminish.

Interface With OtherScientific AreasPlanetary Science

Because reflectance spectroscopy is a technique withinthe broader field of planetary science, it is essential thatthere be strong cross-disciplinary ties amonginvestigators. The program has evolved naturally in thisdirection; however, cross-disciplinary work does notalways fit conveniently within NASA organizational andprogrammatic structures. Funding is usually alongdisciplinary lines, and even conferences and workshopsare often organized by discipline. For example, theplanetary reflectance spectroscopy data set and theinstrumentation and data reduction facilities aresupported mainly through the Planetary AstronomyProgram but the analysis and laboratory studies arefunded mainly through the Planetary Geology andGeophysics Program. The Planetary Atmospheresprogram is also involved. It is essential at this point inplanetary science that no discipline area be isolated.

Among the ways to facilitate communication betweenscientific areas are consortia, coordinated projects, andtopical conferences and workshops. NASA can directlyinfluence the amount of communication amongscientists by its funding actions. For example, there hasbeen discussion recently about the need to have remotesensing specialists and photogeologists work moreclosely. Although some collaboration already exists,interaction between these groups has been limited forthe last 3 years. The small FORSE consortium comprisedworkers in the areas of photogeology, spectroscopy,planetary astronomy, radar, and theory, and includedvarious specialists on individual planets. This groupproduced a series of multidisciplinary papers onplanetary surfaces over a period of about 6 years. Suchcooperative efforts are minimal in today's fundingclimate, owing to restricted funding of investigators' timeand other resources, and to severe restrictions on travel.Thus, at the time in the evolution of the planetaryprogram when we should be integrating the results of

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the past decade in a multidisciplinary way in preparationfor the next generation of missions, we are insteadslipping into increasing isolation.

The solution to this problem lies partly with thescientists and partly with NASA. We suggest that thescientists take the responsibility and the initiative topromote cooperative multidisciplinary efforts (anexample is the successful MECA project). Modestfunding along with programmatic encouragement willbe required from NASA.

Terrestrial ProgramA decade ago reflectance spectroscopy was a minor

part of the scientific study of Earth and of the NASAterrestrial program. Landsat provided images in fourbroad bandpasses which had been chosen foragricultural purposes. Geologists exploited the broadcoverage of Landsat from a photogeological point ofview; however, mineral and rock identifications werenot facilitated by the data available. Tbday NASA isinvolved in an active terrestrial geology program thatis aimed at the use of imaging spectrometers on a spacestation in the 1990s. Imaging spectrometers are beingdeveloped and flown in aircraft. Scientists have foundnew ways to use reflectance spectroscopy in studyingEarth. Geologists in industry use high resolution fieldspectrometers and aircraft-mounted spectroradiometersfor mineral exploration.

The terrestrial program has brought new resourcesinto the area of geological reflectance spectroscopy. Thishas benefited the science; however, it also has placedthe terrestrial program in competition for the personnelresources in the planetary program. The competitionfor experienced personnel will intensify as activitiesrelated to the space station accelerate, for the time framefor the space station overlaps that for the Galileo andMars Observer missions.

We also note that the increasing use of reflectancespectroscopy in terrestrial mineral exploration and othercommercial and government activities has created anadditional draw on the limited personnel resources ofthe planetary program. This is especially evident in thetrend for graduate students trained in reflectancespectroscopy to take jobs in industry and government.A similar problem exists with respect to key technicalpersonnel.

IEducationUniversities are an important part of NASA's research

effort in reflectance spectroscopy. Support for agraduate student can cost as much as $20,000 per year;facilities, equipment, and supplies require additionalfunds. The current funding for the reflectancespectroscopy program is not adequate.

As funding for an investigator diminishes it is oftennecessary to seek other support for a graduate student.Students who are forced to change research topics areunlikely to return to the original field. Students avoidresearch areas in which the prospects for continuityof funding are uncertain. These uncertainties, coupledwith the poor job prospects in the planetary sciences,pose a difficult challenge for principal investigators andNASA program managers who are looking ahead tomeeting the challenges of future missions.

A steady flow of new scientists is necessary forseveral reasons:

Graduate students are an important and costeffective work force for research.Students and young scientists are a majorsource of new ideas and technology.Many of the experienced scientists workingtoday will no longer be active when thecurrently planned missions are flown.

We have also noted previously that students trainedin reflectance spectroscopy may obtain positions in theNASA terrestrial program and in a variety of industriesand government agencies. The few students beingtrained today are not working in the planetary sciences.

IConsequences of FundingActions

Although we have been told that the proportion ofthe Planetary Geology Program funding for reflectancespectroscopy was modestly increased, the funding perinvestigator per year appears to have diminished in thelast 5 years. Furthermore, as mentioned above, for thereflectance spectroscopy investigations planned for newmissions (e.g., MOM/VIMS), measure planning and dataprocessing budgets are a factor of 3 to 5 too low to carryout the required work. This load is historicallytransferred to the basic research program, where itcannot be borne.

We have identified possible scenarios for futuremanagement of the field of reflectance spectroscopy.Although some are not desirable, they are presentedhere.

Scenario 1. Continue the current downward trend insupport per investigator and continue to apportion thebudget cuts among investigators. Research groups ofhigh quality are being squeezed from the program. Afew investigators are receiving grants of $20,000 to$30,000, which is not sufficient to support a typicalindividual stand-alone research project (normallyrequiring about $100,000 per year); thereforeinvestigators depend on other funded projects. It is thecontinuation of this trend that is of primary concern,

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for the broad science coverage and balance of theprogram are at stake.

Scenario 3. A small increase in funding would stabilizethe program, keep pace with inflation, and allow fora maintenance mode in which the program is intact butresources are not adequate to meet the critical missionchallenges ahead.

Scenario 3. If a substantial increase in support wereavailable, the program could be stabilized, and a newlevel of effort could begin on mission-related challenges.Even if such funding increase were to begin in FY 88,there would be a lag period of a few years for gatheringpersonnel and equipment. As discussed above, someinvestigators have taken on other research commitmentsas funding has diminished in the planetary reflectancespectroscopy effort, and these commitments will notbe dropped immediately. As long as a balanced coregroups exists, the transition could be made efficiently.If the program shrinks so that the remaininginvestigators are those who operate on the lowestsurvival budgets (usually those who are not supportinglaboratory facilities), the program will not respondquickly to increased funding.

Scenario 4. A scenario unattractive to someinvestigators is the elimination of some investigators tomaintain level or increased funding for others. This isthe approach of consolidating around a few centers ofexcellence where facilities as well as investigators exist.In this case, it is difficult to maintain a balance, but itpreserves a core capability which can be built on when(if) funding increases.

IProgram InitiativesThe highest priority must be given to stabilizing the

progam, avoiding further deterioration of the fundingbase, and building that base to meet the missionrequirements of the near future.

As a first step in strengthening the reflectancespectroscopy program, immediate measures should betaken to improve communications between the NASAreflectance spectroscopy program management and themission-oriented activities in NASA, especially Galileoand Mars Observer. It is not clear that the missionplanners or even the investigation team leaders areaware of the ongoing research requirements inreflectance spectroscopy, or that the NASA managementis fully appraised of the mission reflectance spectroscopydrivers.

A specific effort should be made to coordinate thereflectance spectroscopy efforts in techniquedevelopment in the planetary program and in theterrestrial program.

It is essential that the investigators in the programwork closely with management to provide informationand support in the efforts to stabilize the reflectancespectroscopy program. It is also important thatinvestigators communicate effectively as a group. Anannual or biannual meeting of investigators andmanagement to discuss research and programmaticproblems would be useful.

Program management can promote efficient use ofexisting resources by encouraging and funding consortiaand cooperative research projects among scientistswithin the reflectance spectroscopy program, andincluding outside investigators.