- <, 7 vc ,Z

AD-765 421

THE POTENTIAL LI F OF POLARIZED REFLECTED LIGHT IN

THE REMOTE SENSING OF SOIL MOISTURE

ARMY ELECTRONICS COMMAND

JULY 1973

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z Reports Control SymbolOSD- 1366

0. .... 0 RESEARCH AND~ DEVELOPMENT TECHNICAL REPORT

*ECOM-5501 12

~ ~THE POTENTIAL USE OF POLARIZED REFLECTED~?~r:LIGT 1N- -THE REMOTE S.1ENSING OF

SOIL MOISTURE

Borry Doll

Atmospheric Sciences L.aboratory

* US Army Electronics Command

White Sartcs Missile Runge, New Mexico 88002

*A

* July 1973

.........

* Approved for public release, distribution unlimited.

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U S Department of Commierce

UNI1W STATES ARMY ELECTRONICS COMMAND -FORT MONMOUTH NWJRE0770

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I- ORIGINATING ACTIVITY (Calpoetei Author) 28. REPORT SECURITY CL'A014.IATIO

Atmospheric Sciences LaborajtoryLCLSIFEWhite Sands Miss'fle Range, New tVexico 88002 bGOP

11- REPORT TtTLE

THE POTENTIAL USE OF POLARIZED REFLECTED LIGHT IN THE REMTE SENSING OF SOIL W~ISTURI

4. OESCRIPTIVL NOTES (7Tp. 01oftpcriond incluoiv detoo)

5. AUTHOR(S) (Plst neeme middle ini~tial feetnems,)

SPI4 Barry Doll[ 8 CACT TC A. VZ70 OAI NO OW PAG&. 17b. No. OF REVSsF ;m AC. CO OR R GRANT NO. 94. ORIGINAlfit6R REPORT NUI43ERIS)

b. PROJECT NO. EO-5

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feld.

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Approved for public release; distribution unlimited.

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S.AlSTRACT

Polar*zatlon of light reflected from soil and san' samrples Is studied as surfacermoisture aýnd textlure of the samples are varied. A ref lectome-ter equipped witha rotating analyzer records the polarization percentage of the ref lected lI ght. 3The percentage of polarization runs from 15.5% for dry soilI to 89% for saturatedsoil , indicating that the polari/.ation method troy be viable Pis a remote sensingZsystem for de~ermi n Ing soIlI mo Istures. Background on 'the me rhods and i uip IIcat ionsof the results are presented.

Ea

DD 1~?41104 73 RSPA* 3OWO,4S. iego -

YC' V..6 Ftycy~?assification

1 Id LINKWD A LINK 0 LINK c

* ___________________________________ H OLZ PIT noIt- WT M06 W

1. Polarization

2. Ref lected Liaht

3. Remote Sensing

seem"CIA104c"IC

F-4

PREFACE

Figure I was provIdad by NASA, Figure 2 by the Department ofMeteorology, UCLA. Figures 3-5 are adapted from graphs

VO 1provided by the Departme~nt of Meteorology, UCLA.

If

I ~CON TENTSPa ge

4INTRODUCTION .

REMODTE SOIL SENSING. .. ...... ........ . . . . .* .5.

POLARIZED REFLECTED LIGHT.... .. .. .. . ... .. .. ..

EXPERIMENTAL PROCEDURE .. .. ..... . . .. . .. .. . .8

7 TEST RESULTS. .. .. ................ ................... 10

P ~FURTHE.RCONS i GRAT IONS............. . .14

SUMMARY. .. ........ .................... ............. 14

LITERATURE CITED .. .... ..... . .. .. .. .. .. . .15

. Preceding page blank

I NTRODUCT ION

The 3bility to rapidly move mechanized equipment over alltypes of terrain is essential to any modern army,. Sincenost of the earth's land surface Is covered by some~ kindof soil, the army must concern itself with problemr of soilirafficability. Some of the physical factors affectingtrafficability include soil type, -texture, comrpaction, andmoisture; slope and relief; the local hydrologic situation;climate; and vegetation type and density. Of these, themost imrportant short-term variable for a particular locationis undoubtedly soil moisture. A change In moisture conten,of soil can ma ke a normally trafficable zone effectivelyimp~assable to wheeled vehicles in a matter of hours.

7"RUEr.IE SOIL SENSING

A number of remote sensing techniques nave been applied tothe study of soils, and a few have been used to look at soilmoisture. Aerial photography can be used to obtain a roughidea of the water content of a soil; one of the tirstGemini photos shows a darkened swath of West Texas soil thathad been damp~ened by a thunder-.torm (Figure 1'. Black and

* white Infrared film can be used to locate water at the surface,3ince any water present will record as black.

*The Army Engineers Waterways Experiment Station has used afour-band radar system at a 15-rreter elevation to study surfacewater and soiI froisture Eli, pp. 52-533. Other organizationsi-,ve tried to apply variou,- types of roaar, including pulsed.

-C rv,,ar and radar scatterometr/, to tho sarre. problem [i, pp. 53-553.

Passive micrcwave radiometry Iiab shown a great deal ofprominse In de-rarmining surface composition and texture,mo~istre content, and layt-ring. The Space General Division

of Aerojel G(-,erai Corp. has done, aoxtensve work in thisara inclu.~ing sove suc:ce-,ful tosts with airborne 5ensors[i, p. 59]. NASA is currontly interested in usinlg polarized

misoa6i aatal ion tu. 5.tudy suf i~(.4~ OI t.JI,5:s . ~

I. Ned~e~a9 S. M., and C. E. &'bllpeux, 1969, "Earth Scler.ceApoI led to Mi ,itr~y Usae of t-atural Terrain," Air Force$jjrvOYS In Ckaphysics, No, 211.

5 Preceding pnge black

N4:4

4

It':..

its' N+

4��*

fl? .4 -

4.I

#- .4 � .,

& WI'

*� j4 4 .- S

A -

t -* .7

'Ij

(4 ft4 e

- 9 - 9- 9� .

4.-' 9 - - -

'A-4

Mi! POLARIZED REFLECTED LIGIHT

Another potentially valuable remcte sensing tool for the studyof soil moisture would involve the phenomenon of the poJarizationof light when It is reflected from natural surfaces. Virtuallyany natural surface alters the polarization properties of lightwhich is reflected from it. In the case of impinging sunlight,

A • which is essentially unpolarized, the resulting reflectedlight will exhibit some polarization. Natural surfaces thereforefall somewhere between the two theoretical extremes ofref lect ion properties:

(1) The Lambertian surface, from which the reflected lightis unpolarized, its intensity Indeoerdon,' of the angleof illumination; and

(2) the classical specular reflector, from which the lightis completely polarized, behaving according toFresnel's laws.

For the purpose of studying reilected earthllight, the earth's

land c-,irface h-s Senerelly been considered to be a Lambertian[3, p.. 45 reflector. tost surface roterials, when dry, reflect

4; light that Is very weakly polarized. Undisturbed water, however,is the closest owron approximtion to a specular reftector,and light reflected from Its surface rr-y be nearly 100%polarized (at least in +he laboratory). As water is added to

• a dry soil, therefore, we can expect that the porcentake ofp* plarization of lIght reflected .rom the sol will •rwt I esteadily as it wore and -wre strongly adopts Mie refle-ti%-properties of water.

rikCause the Lthenogrwna ol ritficcued HTiht aro ntvortlnt toVh

"Study of varour, problem in phy.ics$ 4nd w•o-troloqv, thWrQhas b"••uer. •erte iv , wokdmoHtis nr, . 2oo [43te

uf torN a groaet fwl of it, includinig hi;- Wr owne 'Itv4 atof oth¶?r- *k thji fie*ld o~f poor te$ rlrccted ltpt. In

"9"5, C1, ( n' St1sera. afw r bt thA, withe i.Iti•~ssistanC Sf£o'ikn, teýZ!an stpIdy i ri thve IvflIgioýr

itcrtesof natua surfaceos. Ihgv S.~Qc ~oip

thClen, ~4siStPU, C. 1.Nagarajz RkJcO .4nd Z. Sok:Q-ra, ;,%7,I1twtsti-et1 ont s ti Ar the r'olarizatioln cm Liqht PktIq'cctod b

Nos. 2AF7 19 i62&) SOO 3& Wtpt.. of MierlgUCLA~.

of tjaturb. :ýýrfecos InNrlRoc aisce" pfj

*"L • -r,." v"":. 17S " I I "•I~l l I I• I i • l~ • i17 |I • I- p7r I I I I I I

theoretical backgrounds for their study and methods [3, pp. 4-12],[5], as well as extensive reports of their findings [61. Theyhave been interested melniy in characterizing the polarizationresponse of light in various conbinations of incidence andreflection angles, although they have also varied the surfacecomposition to some extent.

The group at UCLA obtained noticeable differences in polarizationSfo.tcr wha," tcy chear* the rf!ecting surface material. Thisfact suggests that the polarization of the reflected lighTmight be studied to provide information about the surface.During the week of 28 August 1972 - I September 1972, theauthor visited Dr. Rao at his ;oboratory at UCLA to makepreliminary measurements cf the light refieead from surfacesof varying texture and moisture. The experimental apparatusand inbtrumentetion ued (Soue F;gtre 2) *werte &;,-;ar tothose described previousl' by Chen et at. [3, pp. 16-22j,but In their present form they rtln to be described more fully"in a forthcoming paper.

EXPERI ,.ENTAL PROCEDURE

In all the experiments, the illumination source angle waskept conctant (550 00' from the vertical), while the reflectionangle was moved in 6" increments through Wst of the princicalitplane. Since the most signicant results are in the specularhalf-plane (opposite the sour•e), only these orc shown for eachof the tgsts. The reflectonmte:- was equispped with o rotatlnqanalyzor, aad the dogree of plane polarlzation was date.rMinedby

"P K(j - I )pi 4I I (I).Max m .n IX m

whore F is the jacree ot Piano polarizin fnd V and miwire 'e mnaxirnve 'ffd Mit v '& Iradl.aricin transmitteiQk thflf~Uqg "_0 ajfalyZer, V, *)O~lanad by-Ccv son [N, p.

.R. herar, S, T,,"t labor-atory 01ee~ntit cINt C-ara'ceristicý %flecfS*C.0M1atricos5 of 114turaf Surfaces," J. itis.. D.: Aopp I Vhr! ,, .pp. lO57-.

6. Hao, C. k~ 4Vgra.a, aMl lti-%hu C',tqn. 196, "M Atiasof PŽiIarizaticn Features of Light R#ileeted fry DertSand, 'Witle Sand, atld Sol, SciefltiK q apor Uo. 5,.. ,.t .r~6aa.0f e1i•eorvl0', VLA.

,,II'..

¶X

WY

S1MOM

Ft~jujrt.. Lxpc':;rir' 1 •pDparj'ui _onsisting of (A) Quartz-halogenlight carriage, (H) Control panel, (C) Sample Tray, and(D) Rotating-analyzer polarimeter.

The surface material used in the texture-variation experiment wasa dry, sandy, granitic soil, which was separated into fourparticle-size ranges. Samples were placed In trays andsmoothed Oth a screed; results are found in Figure 3. Thesame soil, minus any particles larger than 0.47cm (0.185 in.),was used in the soil moisture tests (Figure 4), along with an

additional sample of white gypsum sand (Figure 5). The

variables introduced in the moisture testý are shown inthe key following Figure 4.

Because of time limitations, we were not able to vary anyproperties other than texture and moisture. In the future,

it would be profitable to study the effects of changing the

microrelief, tracc element composition, and compaction (including

frozen N/s unfroz,)n surfaces).

TEST RESULTS

The results obtained by varying the texture of the soil (Figure3) were relatively uniform. The only significant differencein readings was between the coarsest sample, which wasessential ly a fine gravel, and the three finer samples. Workwith still coarser samples should probably be done to fullyevaluate the effect of particle size on polarization.

The tests done with sand and soil moisture (Figures 4 and 5)revealed a phenomenon which could be exploited by remotesensors. At the optimum reflection angle (approximately60 degrees), polarization of the reflected light varied from15.5% for dry ýoil to '09% for saturated soil, with a nearlylinear progression of values between the extremes. Therange of polarization values Is such that very accuratemoisture determinations should be possible, especial!y ifprevious readings have established a standard for the surfaceiinder scrutiny. In this case, as in many others connectedv:'th remote sensing, it would be quite advantageous to combinedifferent kinds of remote sensors to maximize the obtainableinformation. Passes over an area of interest with IR andpassive microwave sensors, for example, might provideenough compositional data to allow precise moisture determinationswith a polarimeter. Any kind of meteorological data would, ofcourse, be of great help as well (see the following section).

10

REFLECTION 8.cs 530 00'SOURCE ANGLE

FOR ALL TESTS: 00 L --XA vs 49804NA'T-URAL LIGHT

SAMPLE

SYMBOL PARTICLE SIZEso • • <(0.21amm (0.0083")

I x x x BETWEEN 0.59mm (0.0232")and 0.83mm(0.0328)A A AA BETWEEN 0.83mm(O.0328")ond 4.70mm(O.1850")o o 0 0 >4.70rmm (0 . 18 5 0 m)

400

0.~ g.

REFLECTION ANGLE

Figure 3. Dry soil, varying particle size.

S~II

•F *@oo SIALI[ I

So eIIIP..I. MWL 3

S"0000 0

OCOOSLE' SALAAAWE 0

8. .-ui PLEo a 0

MURAL~ LmWr

4 &40 I

*4 go, o

REFLECTION AWLE

LEGEND:

* * . • SAMPLE L DRY, BROWNISH SOIL, PARTICLES SMALLER THAN

4.70mm (0.185") , SMOOTHED WITH A SCREED.

o o 0 0 SAMPLE 2. SAME SOIL, SPRINKLED UNIFORMLY WITH WATER

SURFACE DARKER THAN IN* I. WATER CONTENT: 5.5 %

BY WEIGHT.

x x x x SAMPLE 3. SAME SOIL, MIXED WITH WATER BY HAND. SURFACE

DARKER THAN IN 0'2. USE OF A SCREED CAUSED THESURFACE TO APPEAR TORN. WATER CONTENT: 6.8% BYWEIGHT.

6 A 6 A SAMPLE 4. SAME AS b3, BUT WITH WATER CONTENT OF 12.7%.

SURFACE APPEARED DARKER THAN IN 43.

0 0 0 0 SAMPLE 5. WATER WAS ADDED TO THE SOIL UNTIL IT OBTAINEDTHE CONSISTENCY OF SLIDING MUD. SURFACE HAD ANOVERALL GLEAM.

Figure 4. Sol I, varying moisture content.

12

REFLECTION 0.re 53•00'

SOURCE ANGLE

FOR ALL TESTS:NATURAL LIGHT

SAMPLE

'000

sOSYMBOL CONDITION

0 * 0 * DRY

so x x x x MOIST (6.0% BY WEIGHT). MOIST SURFACE

HAD A SCULPTURED APPEARANCE

~40-

SII

20

U !

R1EFLECTION ANGLE

Figure 5. Gypsum sand, varying moisture content.

13

FURTHER CONSIDERATIONS

!f a polarization analyzer Is to be used as a high-altituderemote sensor, there remains the problem of transmission througha turbid atmosphere. The atmosphere itself can act as apolarizing agent, especially at the shorter visible wavelengths.Transmission of surface infortmtion would be much moreeffective in the yellow, red, and near-infrared bands.Research would be necessary to determine the optimum transmissionbands for various applications, as well as the extent ofdistortions to be expected. Vertical profile meteorologicalInstruments might be-used to help correct for the distortions.Rao and others at UCLA have been studying the problem oftransmission of polarized light for some time, andsolutions are probably within reach.

Since the envisioned sensing system would involve opticalinteraction with soil particles at the surface, any physicalcondttion which tends to limit that Interaction couldconstitute a physical hindrance to the system. A heavyvegetative cover might conceal enough soil to make theresulting polarization percentages meaningless, depending onthe optical properties of the vegetation. A heavy dew couldcause misleading results In early morning readings. Eachof these limiting factors would have to be field-tested fromaircraft before the sensing system could be put into operation.

SUMMARY

Experiments have been performed on the extent of polarizationof light reflected from natural surfaces. Although othervariables remain to be tested, we have already foundthat a change in soil moisture has a profound effect onthe polarization percentage of light ref!ected from the soil.This fact could be used as the basis for a renote sensing systemfor determining surface moistures, specifically through theuse of a rotating-analyzer reflectometer as part of a satelliteinstrument package. Since angle of illumination lind angle ofobservation are so Important to the resulting polarization,a continual monitoring of these factors would have to beperformed by computer to allow an analysis of the results.Information from other sensors would be used to help determinesurface conditions.

14

LITERATURE CIE

p p1. T' Needleman S.??l M. and .t C . E. -oi x 199 "Ert Scienc

Aple to Miitr Us of Nal-a Te-an" i oc

Suvy in Gepyis No 211.

2.p WhthaVcoNSveblcmuiain92

3.CeHisu .R aaaj aadZ pea 97

- I. Neediemn, S. M., and6 C.Effct ofReneu tio P969, pearthSiencApedtMiiryUeof Natural Tefcerr eia ecnaissnc," AirpForedSuvesinGopyics, No.,pp 90591 .

p-I 3. Chnao -h, C. R. Nagaraja, Rao.he, and T. Sekerhia, 19671, ~"Investiationy oferinthen Polfiztihn ofarctLighti ReflectdobMtieofNatural Surfaces," Scetii Rport N. 2, Contract', 4

pp 157,16,2p.9597

6. Rao, C. R. Nagaraja, and Hsi-shu Chen, 1969, "-An Atlas

of Polarization Features of Light Reflected by Desert$and Whte Sndand QII1' SienificRepri N. 3Contract No. F19628-67-C-0196, Dept. of Mateoroiogy, UCLA.

1015

4I

IVIATMOSPHERIC SCIENCES RESEARCH PAPERS'

1. Dicktson, David H., and James R, Oden, Fog Dissipation Techniques for EmergencyUse, January 1972, ECOM-5420.

2. Pena, Ricardo, L. J. Rider, and Manuel Armendariz, Turbulence Characteristics atIHeights of 1.5, 4.0, and 16.0 Meters at White Sands Missile Range, NewMexico, January 1972, ECOM-5421.

3. Miller, Walter B., On Calculati( a of Dynamic Error Parameters for the Rawinsondeand Related S~ystems, January 1972, ECOM-5422.

4. Richter, Thomas J., Pawin Radar Targets, February 1972, ECOM-5424.I5. Blanco, Abel J., and L. E. Traylor, Statistical Prediction of Impact Displacement due

to the Wind Effect on an Unguided Artillery Rocket During PoweredFlight, March. 1972, ECOM-5427.

6. William%, B. H., R. 0. Olsen, and M. D. Kays, Stratospheric-Ionospheric InteractionDuring the Moveineit of a Planetary W&ve in Januar 1967, M&-rh1972, ECOM-5428.

7. Mason, J. B., and J. D. Lindberg, Laser Beam Behavior on a Long High Path, April8. 1)kon . H72, ECogwa 40 I nEperiment Using Helicopter Downwash, April 1972,

i'9. Schieusener, Stuart A., and Kenneth 0. White, Applications of Dual Parameter An-alyzers in Solid-State Laser Teats, April 1972, ECOM.5432.

1.Smith, Jack, Thomas H. Pries, Kenneth J. Skipka, and Marvin Harnilter, Optical10. Filter Function for a Folded Laser Path, April 1972, ECOM-5433.

11. Pries, Thomas H., Jack Smith, and Marvin Hai-niter, Some Observations of Meteor-ological Effects on Optical Wave Propagation, April 1972, ECOM-5434.

.12.Cantrsrael, Survey of Studies of Atmospheric Transmission from a 4w Light Source.. . . t a 21r Receiver, April 1972. ECOM-5435.

13. Lowenthal, Marvn J. The Accuracy of Ballistic Density Departure Tables 1934-I.1972, Apri 1972, ECOM-6436.

14. Barr, William C., Accuracy RequirementA for the Mleasurement of Meteorological Par-ameters Whic Affect Artiller Fire, April 1972, ECOM4-~537.

15. Duchon, C. E., F.V. Brock, M. Am. endariz and J. D. Horn, UVW Anemometer Dy-

Ifi16. Lee, Robert P., Artillery Sounrd Ranging Computer Siwulations, May 1972, ECOM-5441.

17. Doswell, C. A., 111, A W-oDimensional Short-Range Fog Foreca~t Mlodel. May1972, ECOM-5443.

1I& DoeswelL, C. A., I11, An Iterative Method for Saturation Adjustment, June 1972,ECOM-6444.

19.Oonez H. B, Amoipheric Effecta for Ground Target Sig'"ture Modeling 1. At-inospheric Trarmiaaon at 1.06 Mit.rmeteis, Juno 1972, ECOM-5446.

20..5. A Teetwical Manual on the Cbatacto.iaadOeato faCu,.Condvwsation NuliCfocinOtotnUcx ing rUment. June012 1972, ECOM-5447.

2L Waito-, IL W,, Relihilty Test of Electrontics Module, of Wlpte*oWtok Mcai~ingSe-t Ai~NI~hQ.2(XE.4), June 1972. EOOM-5448.

22. Horn, J. D., R. D1. Raynausl1. *nd T. H. Vonder Haar, Sumrv of Te'chniques lnd. irlDla4Vy e! Sequential Images Rw~oevd from deostafionar SateWtcv,June 19772, LV04-5460,

.23. Collett, Edward "Analysi of the Interction of 1Partially PolariW e1 iht with I-.efetxwic Nlte#," ECOM-6451, July 1972 WA) 146 %.42).

24. Collett, Edward, "NIOMat UitCSl FrOrmublaon Of the ftkorfertnC0 LAwa Of F1 ý-en

. . . .. .and Arago,'" EC0M-4152, July 1972 (AD 744 W6)._25 Mardwagber, Reinhold M., "Tho Developraent of Standard lhuttunents for lb"i-

tion M surerwa6 ." ECOM-54M3, July 1972 (AD 74f, SV2&.Mrhubw Reinhold M., "An An*.:'gue TeL+hnique for the In rovemnen of the Fw-n

quericy Response of a TheniJ )adioweter," ECOM4.54.4 July 1912

27. Bonner, R. S., aind H. M. White, Microphysical Observationi of Fog in Redwood Val-ley near A-cata-Eureka, California, July 1972, ECOM-5455.

28. Collett, E., and R. Alterness, "Depolariz~ation of a Laser Beam in a Turbulent Medi-urn"' ECOM-5458, August 1972 (AD 747 886).

29. Cantor, Isral, and Michael Hudlow, Rainfall Effects on Satellite Communicationsin the K, X, and C Bands, July 1972, ECOM-5459.

30. Ibtndhawa, J. S., Variations in Stratospheric Circulation and Ozone During Sel!3ctedPeriods, August 1972, ECOM-5460.

31. Seagraves, Mary Ann B., A General-Purpose Meteorological Rocket Data ReductionProgram, Aug'xst 1972, ECOM- 13.

32. Loveland, R. B., J. L. Johnson, and B. D. Hinus, Differential Magetic MeasurementsNear Cumulus Clouds, August 1972, ECOM-5463.

33. Nordquist, Walter S., Jr., and Dickson, David H., Helicopter Dowuwash Applied toFog Clearing: A Status Sunmmary, October 1972, ECOM-5465.

34. Rider, L. J.., Amnendariz, Manuel, Mean Horizontal Wind Speed and Direction Vari-ability at Heights of 1.5 and 4.0 Meters Above Ground Level at WSMR,New Mexico, October 1972, ECOM-5466.

35& Engebos, Bernard F., Effects of Vertical Wind on Tactical Rockets and ArtilleryShells, November 1972, ECOM-5467.

36. Armendariz, M., and James R. Scoggins, Characteristics of the Turbulent DiffusionParameters as Related to Stability, November 1972, ECOM..5468.

* 37. White, Kenneth 0., James B. Gillespie, Robert Armstrong, and Larry E. Traylor,State-of-the-Art Survey of Meteorological Instrumentation Required- foDetermine Atmospheric Effects -on Airborne Laser Tests, November 1972,

* ECOM-5469.38. Duncan, Louis D., and Barbara J. Richart, Mesoscale Variation of Spectral RadLance

Near 15 Micrometers, December 1972, ECOM-5470.39. Schleusener, Stuart A., and Kenneth 0. White, Solid-State Laser Multiwaveloxigth

Identification. and Display System, January 1973, ECOM-5473.40. Nordquist,.Walter S., Jr., Numerical Approximnations of Selected Meteorological Par,

anieters Related to Cloud Physics, March 1973, ECOM-6475.41. Maynard, Harry, An Evaluation of Ten Fast. Fourier Transorm (FPIT) Programs,

March 1973, ECOM-6476.42. Gerber,- Henann E., Freern Water with Sized Agl Particles -Part 1: A Survey,

March 1973, E29AM-5477.A&. Gerber, Herrawan E .. Fwrerng Water wvith S12ed /%I Particles Part I!: Theortical

Considerations March 1973, RCOM-5478.44. D'Axey, Edward M,. Accuracy Study of the T-9J Radar, March 1973. ECOMM*5480.4& iMiller, Walter B., An Investigation of Ezrimr Introduced into Mote ohrogical ('alcula-

!ions Through Use. of the Hypswaictrice Equation, April 1973, MINI-5481.

46. Miler, Walter V, On Indirect Pmossure Estinmaiov from Nleasuremwnta of Heightandi i~ ieraturo, ApWi 19M3, ECONI-5482.

47. Wuehrt G. S., &Wd R. V. Lme, Apprent 7-Day Period in Vislihity Data at WhitSands hfisiale IlAnfi, New M~exiico. April 1073, ECOMN -5484.

48 Suingle, Donald M4.. and flayrnond Reflucci, Improvecd Sound flanging Location ofE~nemuy Artillery, Apri 1973, =CM-5486.

.49. Limlba&g Jam"c D., and David G. S "nyde-r. ltrnito of the UrOtcAl At".owtiohCoeafcet oi Powdered Maft66al Whose Partice Sire D iptiutio6 and

Rflelattite -ni.m* Ate Not Kilo*~ "Aptil 19"3, E(CON~I-481-* . 50. llubio, 1Re~ro, "Winter Anonialous RAdio Wave Alwwlion Days at 3211 N LAttudb

And prevalent soar iladiatio".,' ECOmi-&4$, may 1973SL1 NowiAd~ti WV. S_. "Ata from 4 Fog flisprual Experiumet Usiog 1ie~ioapler Down-

wash' EOMS56,Mly 1973.52. %inn, Joseph H. 7 '4(timump WindI Roundinp~ and- Army Fallout Prodi4.iw Amcur-

2665 EC0M548$9, May 1973.63. illt, altr B. ad Dnal R.Veaey~"An Integrated- Emrr Dericriptn of Active

amid Passive I1Uloom Track-n Systems." ECOM4-SWO, June 1073.U5. Dlo4 lHatn, "The Potential Use of Polatized HletkcWe 14;h in the Reo~t& Seasing

Of So11 Moistue". ECOM4SOI, July l073.