12
REPORT DOCUMENTATIOI, PAG AD-A255 374 Pubh( rCt*O,.nq burden tot ths (Oth I C01Ofi of ,nformation 1.1 "t.moted to a.CqC -Ou.' o er wO r a wic, g.therin and ma_. nta.nnq th data needed. Sn* co..aletng and revewng the CIleton of nfom. onI|II EIE of" cotfcc¶,on of Mformation. including iruqgesttoni, for qoau'Tn thIS b.udel' to Vaierr.ftqon -itadaoar hNli l UElE iili I Diont H-ghq ai. S.uot 1104. ArIth9toM. VA 22202-.3rU a&n tO the Ot',ce of aAn0q.*ent and Budge •- 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE " 124-27 March 1992 Scientific Paper 4. TITLE AND SUBTITLE S. FUNDING NUMBERS k " jr Azimuth Determination Using GPS Short Baseline Carrier Wave Interferometry 6. AUTHOR(S) Mahlon C. Hawker 7. PERFORMING ORGANIZATION NAME(S) AND ADORESS(ES) B. PERFORMING ORGANIZATION U.S. Army Topographic Engineering Center REPORT NUMBER ATTN: CETEC-LO Fort Belvoir, VA 22060-5546 R-172 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADORESS(ES) 10. SPONSORING/MONITORING AGENCY REPORT NUMBER 11. SUPPLEMENTARY NOTES 12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; Distribution is unlimited. 13. ABSTRACT (Maximum 200 words) The U.S. Army Topographic Engineering Center (TEC) is involved in research regarding the determination of azimuth by measurement of the carrier phase of GPS satellite signals between two or more antennas. TEC awarded three first generation contracts to develop a GPS Azimuth Determining System (GPS ADS). Presented is a discussion of the three approaches, and test data from limited Government tests of the original systems. DTIC "he1199Z U 14. SUBJECT TERMS 15. NUMBER OF PAGES Azimuth determination 10 GPS satellite signals 16. PRICE CODE 17. SECURITY CLASSIFICATION ItI SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) P-wicbd bv ANSI Sta 139.-1 296-IO

REPORT DOCUMENTATIOI, PAG · The Adroit antennas were removed from their mount and attached to a roof top fixture which allows the long baseline to be spaced 0-842 meter, 1.498 meters,

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Page 1: REPORT DOCUMENTATIOI, PAG · The Adroit antennas were removed from their mount and attached to a roof top fixture which allows the long baseline to be spaced 0-842 meter, 1.498 meters,

REPORT DOCUMENTATIOI, PAG AD-A255 374Pubh( rCt*O,.nq burden tot ths (Oth I C01Ofi of ,nformation 1.1 "t.moted to a.CqC -Ou.' o er wO r a wic,g.therin and ma_. nta.nnq th data needed. Sn* co..aletng and revewng the CIleton of nfom. onI|II EIE of"cotfcc¶,on of Mformation. including iruqgesttoni, for qoau'Tn thIS b.udel' to Vaierr.ftqon -itadaoar hNli l UElE iili IDiont H-ghq ai. S.uot 1104. ArIth9toM. VA 22202-.3rU a&n tO the Ot',ce of aAn0q.*ent and Budge

•- 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE "

124-27 March 1992 Scientific Paper4. TITLE AND SUBTITLE S. FUNDING NUMBERS k " jr

Azimuth Determination Using GPS Short BaselineCarrier Wave Interferometry

6. AUTHOR(S)

Mahlon C. Hawker

7. PERFORMING ORGANIZATION NAME(S) AND ADORESS(ES) B. PERFORMING ORGANIZATION

U.S. Army Topographic Engineering Center REPORT NUMBER

ATTN: CETEC-LOFort Belvoir, VA 22060-5546 R-172

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADORESS(ES) 10. SPONSORING/MONITORINGAGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Approved for public release;

Distribution is unlimited.

13. ABSTRACT (Maximum 200 words)

The U.S. Army Topographic Engineering Center (TEC) is involved in

research regarding the determination of azimuth by measurement of the carrierphase of GPS satellite signals between two or more antennas. TEC awarded three

first generation contracts to develop a GPS Azimuth Determining System (GPS ADS).Presented is a discussion of the three approaches, and test data from limited

Government tests of the original systems. DTIC

"he1199Z U14. SUBJECT TERMS 15. NUMBER OF PAGES

Azimuth determination 10GPS satellite signals 16. PRICE CODE

17. SECURITY CLASSIFICATION ItI SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACTOF REPORT OF THIS PAGE OF ABSTRACT

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIEDNSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

P-wicbd bv ANSI Sta 139.-1296-IO

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GENERAL INSTRUCTIONS FOR COMPLETING SF 298

The Report Documentation Page (RDP) is used in announcing and cataloging reports. It is importantthat this information be consistent with the rest of the report, particularly the cover and title page.Instructions for filling in each block of the form follow It is important to stay within the lines to meetoptical scanning requirements.

tlock 1. Agency Use Only (Leave blank). Block 12a. Distribution/Availability Statement.Denotes public availability or limitations. Cite any

Block 2. Report Date. Full publication date availability to the public. Enter additionalincluding day, month, and year, if available (e.g. 1 limitations or special markings in all capitals (e.g.Jan 88). Must cite at least the year. NOFORN, REL, ITAR).

Block 3. Type of Report and Dates Covered. DOD - See DoDD 5230.24, DistributionState whether report is interim, final, etc. If See o n Technicalapplicable, enter inclusive report dates (e g. 10 Documents.'Jun 87 - 30 Jun 88). DOE - See authorities.

Block 4. Title and Subtitle. A title is taken from NASA - See Handbook NHB 2200.2.

the part of the report that provides the most NTIS - Leave blank.

meaningful and complete information. When areport is prepared in more than one volume, Block 12b. Distribution Code.repeat the primary title, add volume number, andinclude subtitle for the specific volume. Onclassified documents enter the title classification DOD - Eave blank.in parentheses. DOE - Enter DOE distribution categories

from the Standard Distribution for

Block S. Funding Numbers. To include contract Unclassified Scientific and Technical

and grant numbers; may include program Reports.

element number(s), project number(s), task NASA - Leave blank.

number(s), and work unit number(s). Use the NTIS - Leave blank.

following labels:

C - Contract PR - Project Block 13. Abstract. Include a brief (MaximumG - Grant TA - Task 200 words) factual summary of the mostPE - Program WU - Work Unit significant information contained in the report.

Element Accession No.

Block 6. Author(s). Name(s) of person(s) Block 14. Subiect Terms. Keywords or phrasesresponsible for writing the report, performing identifying major subjects in the report.

the research, or credited with the content of thereport. If editor or compiler, this should followthe name(s). Block 15. Number of Pages. Enter the total

number of pages.

Block 7. Performing Organization Name(s) and

Addressles). Self-explanatory. Block 16. Price Code. Enter appropriate price

Block 8. Performing Organization Report code (NTIS only).Number. Enter the unique alphanumeric reportnumber(s) assigned by the organizationperforming the report. Blocks 17.- 19. Security Classifications. Self-

explanatory. Enter U.S. Security Classification in

Block 9. Sponsoring/Monitoring Agency Name(s) accordance with U.S. Security Regulations (i.e.,

and Address(es). Self-explanatory. UNCLASSIFIED). If form contains classifiedinformation, stamp classification on the top and

Block 10. Sponsoring/MonitoringiAqency bottom of the page.Reoort Number. (If known)

Block 11. Supplementary Notes. Enter Block 20. Limitation of Abstract. This block mustinformation not included elsewhere such as: be completed to assign a limitation to the

Prepared in cooperation with...; Trans. of...; To be abstract. Enter either UL (unlimited) or SAR (same

published in.... When a report is revised, include as report). An entry in this block is necessary ifa statement whether the new report supersedes the abstract is to be limited. If blank, the abstractor supplements the older report. is assumed to be unlimited.

Standard Form 298 Back (Rev. 2-89)

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AZIMUTH DETERMINATION USING GPS SHORT-BASELINE CARRIER WAVE INTERFEROXETRY

Mahlon C. HawkerPhysicist

U.S. Army Topographic Engineering Center* FortBelvoir. Virginia 22060-.5546

"Telephone (703) 355-2799

ABSTRACT.

The U.S. Army Topographic Engineering Center (TEC) is involved inresearch regarding the determination of azimuth by measurement ofthe carrier phase of GPS satellite signals between two or moreantennas. TEC awarded three first generation contracts to developa GPS Azimuth Determining System (GPS ADS). Presented is adiscussion of the three approaches, and test data from limitedGovernment tests of the original systems.

INTRODUCTION

Since the early 1960's, the TEC has been investigating and usingsatellites to determine position. Most recently, TEC has beenstudying the Global Positioning System (GPS) and it's applicationto tactical operations. The use of GPS broadcast signals todetermine azimuth was part of these studies. These studies showedthat azimuths could be accurately determined using the standard GPSbroadcast information.

In May 1989, TEC awarded three contracts for the design anddelivery of technology demonstration models of azimuth determiningsystems utilizing modified commercial GPS positioning receivers.The intent of the program was to demonstrate the feasibility ofdetermining azimuths of an accuracy of 0.5 to 3 mils, in real time,utilizing GPS receivers in a portable field equipmentconfiguration. Contracts were awarded to: Magnavox AdvancedProducts and Systems, Torrance, California; Texas Instruments (TI),Plano, Texas; and Adroit Systems, Alexandria, Virginia. The threetechnology breadboard units were successfully demonstrated to theU.S. Army Field Artillery School on September 27, 1990.

DESCRIPTIONS OF THE SYSTEMS

The TEC approach was to utilize Li carrier phase short baselineinterferometry to determine an angle between the antenna baselineand each of three or more satellites. The phase difference L COS0 is the sum of N integral phase cycles, each cycle determined bythe Li carrier wavelength of 19 cm and a residual phase of lessthan 3600. The integer number N must be known in order to resolveangle ambiguities, the solution to this determination being themajor difference among the three approaches. Solving three or more

92-23950

92 8 28 052

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simultaneous equations, one for each satellite used in the azimuthdetermination, gives the orientation of the antenna baseline withrespect to the satellites and thus can be referred to the earth'ssurface. The approach selected by Adroit Systems, Alexandria,Virginia utilized a dual baseline antenna.

The long baseline (0;85 meter) antenna pair resolves the measuredphase into precise multiple solutions.. Each quadrant (9b0) hasmultiple solutions which exactly fit the residual phasemeasurements. Making simultaneous measurements to multiplesatellites increases the total number of solutions. Only onesolution is correct, but the residual differences *are so similarthat selection of one correct solution is very time-consuming anderror-prone involving many iterations and the determination of thelowest residual solution.

Adroit's solution was to use a very short baseline (0.14 meter)antenna pair that resolves an angle to only h to 1 degree. Thiscoarse angle determination is not accurate enough to satisfy theaccuracy requirements of the users, but it is more than adequate todetermine which of the multiple solutions is correct. The shortbaseline has only two ambiguous solutions which are so far removedfrom the connect solution as to be inconsequential.

The Magnavox Marine Systems division approach used a dual frequency(Li and L2) "wide-lane" ambiguity solution method. Subtracting theL2 signal from the Li gives an effective wavelength of 86 cm. Aswith the Adroit approach, the accuracy of the 86 cm. angledetermination does not meet the required specifications, but theambiguous solutions are sufficiently far apart that the correcthigh resolution (Li) solution can be selected.

Texas Instruments utilized a rather straight forward approach,using a two antenna single frequency (Li) 1 meter baseline, anddepending on mathematical computations to resolve the correctsolutions. The TI-420 receiver used incorporated a two stateKalman filter, the only system to do so.

RESULTS OF TESTING

All three systems were demonstrated to the U.S. Army FieldArtillery School, Fort Sill, Oklahoma in September 1990. Theresults (See Figure 1) were obtained during an informaldemonstration by contractor personnel using their own measuringtechniques, which are different for each system. The Adroit datais unique in that it was collected over a period of 1h hours, asopposed to the approximately 15 minute data collection periods of 3r

the other two. It should be noted that all subsequent tests of thesystems at Fort Belvoir, Virginia, by TEC showed results consistent 0with the Fort Sill, Oklahoma data when using the same techniques. 0

Figure 2 shows the results of the three systems located parallel toeach other and separated by three feet. They were not boresighted .to a common azimuth, as the intent was to determine their responses./

tY Cvdon

MC QUtALrrTW OIECTED 3 Dlint -SpecalL

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over a period of time. This figure is a graphic example of thelarge differences in the response of the three technologies to what.is essentially the same input. While the ultimate output of eachsystem is a digital azimuth display, the plots of these azimuthvalues bear little resemblance to each other over an extendedperiod of time.

Multipath tests using these systems are. not considered to beeffective. The greatly varying responses to what is assumed to beeffectively the same stimuli negates any real attempt at using onesystem as a standard "reference" unit under benign, no multipathconditions (if this is possible),. and introducing deliberatemultipath conditions to the. second instrument. Only two identicalmatched and calibrated ADS units should be used to try to determinethe effects of multipath at a particular location. We do not havethis capability at this time.

The Adroit antennas were removed from their mount and attached toa roof top fixture which allows the long baseline to be spaced0-842 meter, 1.498 meters, and 2.216 meters. Figures 3, 4, and 5show one half hour of 0.842 meter data, recorded every 10 secondson four different days. Three days are consecutive and all timesare referred to the same sidereal time. The July 31 through August2 data show excellent correlation. It should be noted that themajority of the descenders, momentary large negative excursions inthe data average, occurred on August 2. These momentary excursionsare a result of measurement and computation errors attributed tothe hardware and should be disregarded. The exact mechanismsinducing these errors have not been determined.

Figure 6 data shows the effect of rotating the mounting structure900 CCW. The time corresponds to the August 1 and 2 1.498 metersbaseline data. Some of our data indicates the presence of a one-hour cyclic variation in calculated azimuths with peak-to-peakvariations of nominally 10 mils to as much as 20 mils.

CONCLUSION

TEC has successfully demonstrated the ability to measure azimuthsusing short baseline interferometry with GPS carrier phasemeasurements. The initial proof-of-concept brassboarddemonstration units did not achieve all design and per~ormancegoals but did identify several problem areas that requireaddressing in our follow-on work. The ability of our crude firstgeneration system to achieve an 8-mil probable error accuracyactually exceeded our initial expectations.

TEC has prepared specifications for a second generation ADS whosedesign will specifically address those problem areas presentlyidentified as major accuracy degraders. The U.S. Army FieldArtillery School, the Multiple Launch Rocket System (MLRS) andTrailblazer are actively involved in setting the requirements. Itis anticipated that the second generation ADS will be sufficientlyperfected so as to lead directly into full scale development for

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several Army weapon systems.

The Adroit system has been modified by the manufacturer to add acarrier phase logging capability and some software enhancements.An external 386 laptop computer is now used as a display and datalogging facility. New antennas incorporating improvedenvironmental shielding have been added.

A request for proposals has been issued for two second generationADS procurements. Specifications have been tightened to the 0.4 to1.0 mil range to meet published requirements for MLRS and otherartillery systems.

Page 7: REPORT DOCUMENTATIOI, PAG · The Adroit antennas were removed from their mount and attached to a roof top fixture which allows the long baseline to be spaced 0-842 meter, 1.498 meters,

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Page 8: REPORT DOCUMENTATIOI, PAG · The Adroit antennas were removed from their mount and attached to a roof top fixture which allows the long baseline to be spaced 0-842 meter, 1.498 meters,

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Page 11: REPORT DOCUMENTATIOI, PAG · The Adroit antennas were removed from their mount and attached to a roof top fixture which allows the long baseline to be spaced 0-842 meter, 1.498 meters,

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