1971 (8th) Vol. 2 Technology Today And The Space Congress® Proceedings Tomorrow

Apr 1st, 8:00 AM

Geodetic Application of Satellite Data

Thomas O. Seppelin Chief, Research Division, USAF Aeronautical Chart & Information Center

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Scholarly Commons Citation Seppelin, Thomas O., "Geodetic Application of Satellite Data" (1971). The Space Congress® Proceedings. 2. https://commons.erau.edu/space-congress-proceedings/proceedings-1971-8th-v2/session-15/2

This Event is brought to you for free and open access by the Conferences at Scholarly Commons. It has been accepted for inclusion in The Space Congress® Proceedings by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. GEODETIC APPLICATION OF SATELLITE DATA

Thomas 0. Seppelin Chief, Research Division USAF Aeronautical Chart & Information Center St. Louis, Missouri

ABSTRACT 2. GEOMETRIC APPLICATION OF SATELLITE DATA

The Aeronautical Chart and Information Center has a. Data Handling used the data obtained from the Geodetic Satellite Program in a number of ways. Our investigations Optical observations are available for both are divided into two separate categories which active and passive satellites—ANNA-IB, GEOS I support the development of a World Geodetic System and GEOS II, and ECHO I and II, and the PAGEOS both directly and indirectly. The geometric satellites. Active satellite data from the application has been specific point positioning National Aeronautics and Space Administration for the Test Ranges and the densification of (NASA) Geodetic Satellite Data Center can be used geodetic control in South America. The dynamic just as it is received. However, corrections must application has been concerned primarily with be applied to passive satellite observations determination of an earth gravitational model and before they can be used for geometric geodesy pur­ tracking station locations from a combination of poses. optical and electronic data supplemented with existing surface gravity anomalies. The status A polynomial adjustment program is used with of the various efforts is presented. passive data to adjust for time delay, correct the phase angles, and compute fictitious simultaneous The Air Force will obtain Geoceivers during 4th observations where camera shutters had not been quarter, FY 71, to replace the optical systems. synchronized. The geometric triangulation program A tri-service test has been designed for the then adjusts the "unknown" to the constrained period July-October 1971. The test objectives camera station positions. The unknowns are relat­ are presented along with results of simulated data ed to one or more camera positions already refer­ from the proposed deployment schemes. enced to a specific geodetic survey system,

b. Previous Applications 1. INTRODUCTION As I said earlier, the geometric application As the Air Force data reduction center, the Aero­ of satellite observational data at ACIC has been nautical Chart and Information Center (ACIC) has directed toward positioning specific points. This used all types of satellite observational data in diagram illustrates three of the projects which we various ways and is investigating other applica­ accomplished with satellite data. Figure 1. The tions. Basically, our studies are divided into network in "a" was used to position the various two separate categories—geometric and dynamic—­ downrange tracking sites of the Eastern Test Range both contributing to the improvement of the global (ETR) to Cape Kennedy on the North American Datum geodetic system. The geometric aspect of satel­ 1927 (NAD-27) and the Cape Canaveral Datums (CCD). lite geodesy at ACIC is involved with the applica­ This adjustment was completed in July 1966. tion of optical observational data for position­ ing specific sites while the dynamic aspects The station configuration used for the Bermuda embrace the integration of optical and electronic adjustment is shown in "b". The camera site in data for developing an improved earth gravitation­ this project was colocated with range tracking al model (EGM), deriving station shifts, and com­ instrumentation which was also located in terms puting a representative geoid. of NAD-27 and CCD. The scale (baseline) for the adjustment was provided by holding the positions I intend discussing the current status of the geo­ at Hunter AFB and Aberdeen, MD, fixed. The survey metric phase at ACIC and, very generally, the effort, data reduction and adjustment were com­ results we have achieved to date. I have included pleted in October 1967. considerably more detail concerning the dynamic aspects because this is a developing phase. The The adjustment of Johnston Island "c" was com­ Army, Navy, and Air Force are going into an oper­ pleted in 1968. This was a particularly inter­ ational test of a new data acquisition system esting project because it was the first time that (known as the Geodetic Receiver) this Summer. We data observed simultaneously with different bal­ intend using both short and long arc techniques listic camera systems was successfully combined to evaluate the capability of the equipment, for a precise station location. The National therefore I have included information regarding Ocean Survey (formerly the US Coast and Geodetic some of our tests of both procedures. Survey) was observing with BC-4 cameras on Maui,

15-1 Wake, and Christmas Islands for the PAGEOS ¥orld is indicated in Figure 5. deployed a PC-1000 camera to Network so we both observed simultaneously. All plate The data is merged in the solution when Johnston and available and reductions were accomplished at Baker-Nunn and Doppler observations are measurements time span. results showed that simultaneous for the same satellite over the same ACIC. The as was the case observations from more than one camera system can When integration is not possible, of arcs was increased so be combined for accurate geometric satellite with Beacon C, the number were able to achieve an internal that both types of data are included. In addition positioning. We will of better than one part in 750,000 in to arc parameters, a total of 455 parameters precision values for the solution, be determined including geocentric station longitude, latitude, and height above the and 13 optical c. Current Status of Geometric Phase reference ellipsoid for 34 Doppler stations; a gravitational model consisting of degree (n) 17 We are presently completing the computations tesseral harmonics complete through of resonance terms. for the South American Densification Project, and order (m) 15; and 7 pairs scheme is an integral part of the worldwide This data is geometric satellite triangulation (PAGEOS World We have found that, if satellite tracking densify the World Network, the Air Force to be used for gravitational model computations, Net). To a partic­ (9) sites with PC-1000 cameras and the orbital perturbations resulting from occupied nine than the simultaneously with four BC-4 cameras in ular harmonic coefficient must be greater observed of the America. The diagram in Figure 2 shows our "noise" level (the observational error) South of the coef­ work superimposed on the South American control in data. We have used current estimates magnitudes of the area. ficients to compute approximate perturbations through degree and order 24. The for Preliminary results of the computations indi­ results indicate that most perturbations 24 are less cate achievement of relative accuracies ranging coefficients from degree 14 through terms. from one part in 300,000 to one part in 600,000. than 10 meters except for the resonant future tracking The Air Force work is being done in cooperation Consequently, extreme accuracy in degree and order with the Pan American Institute of Geography and data is necessary if the higher It will contribute ultimately coefficients are to be determined. Furthermore, History (PAIGH). are readjustment and unification of the entire satellites at lower altitudes and inclinations to the data. South American control system into a homogeneous needed to supplement current tracking survey system referenced to the PAGEOS World Net. It is significant to note that ACIC pioneered the Completion of the South American project will technique of merging all types of observational surface gravity— virtually phase out the optical geometric era of data—optical, electronic, and satellite geodesy in the Air Force. We are redi­ for gravitational model studies. our effort into the dynamic aspects of recting procedure for satellite geodesy with emphasis on merging all We are also working with another This method is types of observational data and full exploitation the analysis of satellite data. of both the long and short arc techniques. known as short arc.

3. APPLICATIONS OF DYNAMIC SATELLITE DATA 4. SHORT ARC TECHNIQUES uses the The past few years we have been working toward In essence, the short arc approach long arc improved gravity models through solutions which qualities of both the geometric and length of the integrate worldwide satellite and surface gravity (dynamic) approaches in that the orbital revo­ data. Extensive studies have been made, and are (short) arc is always less than one of gravitational continuing, to establish practical weighting lution. Consequently the effects determination schemes for the combination of electronic, optical, model errors on tracking position and surface observation data. are minimized. into an current effort is directed toward computing The short arc concept has been developed Our for deter­ with long arc techniques an expanded set of har­ advanced satellite applications program of satel­ monic coefficients from satellite data supplement­ mining geodetic positions with a variety we use ed with surface gravity anomalies. Data from 15 lite observational data. The procedure is being processed. All of the arcs in will handle any combination of optical and elec­ satellites to the data set are 18 days in duration except those tronic directional or ranging observations which are only 15 days because of adjust large geodetic networks. In a study from 1966-5A 171 data. The arcs in the solution were completed recently, we used combinations of limited adjust­ selected because of distribution of data, residual satellite passes in a short arc geodetic orbital characteristics, etc. The ment to improve the coordinates of 29 observing patterns, with satellites, orbital characteristics, and the stations. The results of the adjustment spherical number of arcs from each are tabulated in Figure 3. Hunter AFB, GA, as the origin show a The network of observing stations is shown in standard error of approximately 3.5 meters. Figure 4 and the coverage of mean gravity anoma­ lies to be merged with the satellite tracking data

15-2 5. GEOCEIVER 6. DATA SIMULATION

This is the new data acquisition system I mention­ To validate computer software for the test, we ed. It is known as the Geodetic Receiver but is simulated Geoceiver data to test our short arc more commonly referred to as the Geoceiver. It procedure and its capability for determining will become the primary survey instrument for the unknown positions relative to known stations. Air Force by FY 72. While the Geoceiver may not Data was also simulated with the same Geoceiver offer any improvement in observational accuracy tracking network to evaluate the geocentric posi­ over the Doppler TRANET (Transit Navigation), it tioning capabilities of our long arc technique. is quite compact and highly portable with minimum The data simulations for the long arc tests were logistic problems. The Geoceiver is a portable supplemented with a 21 station Doppler TRANET satellite tracking system designed to recover tracking system. The tracking data for both the Doppler and ionospheric refraction data from geo­ short and long arc tests was simulated without detic and navigational satellites. For each satel­ "noise" and with varying levels of "noise". Ini­ lite pass over the equipment site, the Geoceiver tially, all data was simulated as range differ­ acquires the output signal from the satellite, ences. processes the signal, and punches signal data on paper tape. Once set up by an operator and in The data generation capability of the long arc operation, the Geoceiver can be left untended. technique was used to simulate both the Geoceiver and Doppler TRANET data. While the equipment will Fundamentally, the Geoceiver consists of three track several Navy navigation satellites for sev­ major components—antenna, radio receiver, and eral weeks in the field test, data simulation was recorder. The antenna is a portable assembly with limited to a single navigation satellite for a hemispherical radiation coverage for the reception period of one week. The satellite (67 92A) has a of both vhf and uhf satellite signals. The cylin­ semimajor axis of 7446 km, an eccentricity of drical body is a sealed unit and no tuning or 0.006, and an inclination of 89923. It has nodal adjustment is necessary. Azimuth radiation cover- period of approximately 107 minutes and is reso­ for the antenna is circular (omni-directional). nant with the 13th order harmonics. The gravita­ Vertical radiation coverage provides optimum hemi­ tional model developed by the Smithsonian Astro- spherical energy distribution for the associated physical Observatory (SAG) in 1969 was used to Geoceiver equipment to receive satellite signals. simulate the gravitational forces affecting the (There is a 30° null period at the zenith—15° satellite. Drag and radiation pressure forces on either side.) were omitted and a 15° minimum elevation angle was assumed for all tracking data (no data was simulat­ The radio receiver consists of 12 subassemblies ed until the satellite was 15° above the horizon). housed in a single unit which provides an air tight enclosure. All subassemblies are mounted so a. Short Arc Tests that all test points and cable connections are easily accessible. The respective modules are Although the short arc software includes an easily replaceable for maintenance and test pur­ extensive error modeling capability and other valu­ poses. able features, the ephemeris generator uses a power series solution to the equations of motion The recorder receives information from the radio with a gravitational model truncated to degree and receiver and punches it on paper tape. The paper order four. For this reason, one of the objectives tape provides a method for storing data from sev­ of this test is to evaluate the effect on the eral satellite passes and forwarding the accumu­ results of short arc computations of the use of lated data to a central processing station from the truncated gravitational model as opposed to an any telegraph facility. Approximately 80 inches extended model. We also want to determine the of tape are required to store the information from effect of errors in the Geoceiver data on station each satellite pass. positioning. Therefore, four different sets of data were simulated on the basis of the assump­ All units are stored in five transit cases. Since tions necessary to realize our objectives. they are not wrapped or stored in preservative, unpacking simply means removing them from the Case I. Here the gravitational model was cases. The recorder operates from the transit truncated at degree and order four to be compat­ case. ible with the short arc ephemeris generator. The adequacy of the test data can then be verified and Various tests have been simulated for Geoceiver any significant differences between the short arc deployment with stations positioned along the and long arc computer software determined. The National Ocean Survey (formerly the USC&GS) High data in Case I was generated without noise (error Precision Traverse within the continental limits free). of the United States. All of the stations select­ ed for the simulations have already been oriented Case II. In this set of data the SAO gravita­ to the North American Datum 1927 with gravimetric, tional model was truncated to degree and order Doppler, or other satellite observational data so thirteen plus selected higher degree terms. This that there is a good basis for comparison. data set was also simulated without noise to com-

15-3 the coordinate differ­ with Case I for the effects of the truncated Figure 7. In all cases, pare (generation) minus solu­ gravitational model on the relative positioning of ences are data simulation stations forming the test tracking network. tion parameters. Case I with perfect data Case III, This set has the same gravitational The values computed in model are essentially the same as model as Case II but the data is modified (degrad­ and a truncated in Case II with perfect data and a ed) by adding noise at the +2 meter noise level. those resulting full gravitational model. Results of Cases I and simulations provided enough Case IV. The data here is the same as Case II II also show that the relative positioning to that the noise level is increased to +5 data and geometry for except in any coordinate component. meters. Cases III and IV are designed to test the approximately 4 meters effects of varying noise levels. The results of short arc Case III show that the longitude and height The Geoceiver data simulated for the short precision of the geodetic from range differences to components of the station coordinates deteriorates arc tests was converted +2 which is directly com­ to 10 and 7 meters, respectively, with the cycle counts in a form of these Geoceiver data. The short meter noise level. Further deterioration parable with nominal 20 meters, recovered the original range two components to approximately 25 and arc preprocessor the +5 noise to 0.1 meters and time was recovered respectively, is demonstrated with differences absence of degra­ in all cases. The seven-day arc pro- level in Case IV. The apparent precisely is no doubt the network passes for the stations expected dation in the latitude values duced 22 of the satellite to participate in the operational test. result of the 90° inclination where the North-South and South-North passes are The use of more data, b. Long Arc Tests fairly well balanced. especially supplementary data for a satellite at probably improve the The sub-program of the long arc technique a lower inclination, would and height determinations in which performs single arc reductions for arc pa­ geodetic longitude and unknown station posi­ Cases III and IV. I remind you that all short rameters, data biases, position­ for the following tests. Only arc accuracies are in terms of relative tions was used the known station positions data generation cases were necessary in these ing capabilities where three centered. tests because both the data generation and the may or may not be earth single arc reduction sub-programs have the same I of the long arc tests show gravitational model capability. The findings in Case the capability of the technique to recover station and a set was generated with the same coordinates to one meter with errorless data Case I. This and III show model as short arc Cases II, III, known gravitational field. Cases II SAG gravitational commensurate data for the 21 Doppler TRANET sta­ a deterioration in accuracy roughly and IV. The into the Geo­ and the eight Geoceiver stations was gener­ with the noise levels introduced tions Case II and +5 meters without noise to evaluate the adequacy of the ceiver data—h2 meters in ated noted that these long arc technique to establish positions in an in Case III. It should be of the effect of noise error-free mode with the same gravitational model results are on the basis any of the effects of in both operations (data generation and single arc only. They do not include on the long arc technique. reduction). gravitational modeling

Case II. The data in this set was generated with the gravitational model used in Case I and a 8, CONCLUSION level of +0.01 cycles/second and +2 meters, noise that these tests respectively, for the Doppler TRANET system and To conclude, I want to emphasize and, as such, are only the Geoceiver simulations. are strictly simulations indicative of the conditions and assumptions of be This data set differs from Case II the simulations. We know that errors can Case III. at many noise level assumed for the Geoceiver introduced into the observational data only in the if I did it was simulated at +2 meters in Case points and I would be less than candid data. Where test assumed at the +5 meter level for this not warn against undue optimism over our II, it is short arc set. Both Case II and III were designed to results, You must keep in mind that the data positions so the effect of noise at varying levels on the method is strictly relative—the test respect to the long arc positioning capability. derived are accurate only with accuracy of the "known" stations. derived with 7. COMPARISON OF TEST RESULTS On the other hand those positions long arc techniques are geocentric in the truest of the Geoceiver stations at Belts- sense and are a requirement for many applications. The positions simulations Homestead, and Albuquerque were assumed However, our results for the long arc ville, arising from known for all of the test computations and the do not include any of the problems five were treated as unknowns. The gravitational modeling. Since we know these remaining effort is results of the short arc tests are tabulated in errors are substantial, a continuing earth 1 s gravitation- Figure 6 and those for the long arc technique in necessary to better define the

15-4 al field especially for the Post 1970 WGS that is currently in work.

ILLUSTRATIONS

Figure 1. Geometric Applications. Figure 2. South America Densification. Figure 3. Satellite Orbital Data. Figure 4. Baker-Nunn and Doppler TRANET Stations in ACIC Gravitational Model Normal Matrices. Figure 5. Gravity Data for l°x 1° Mean Anomalies. Figure 6. Short Arc Test Results (Values in Meters). Figure 7. Long Arc Test Results (Values in' Meters).

(To request copies, refer to ACIC Technical Paper Number 71-1.)

SEMMES ABERDEEN

a. EASTERN TEST RANGE (TRINIDAD) b. BERMUDA

WAKE IS.

c. JQHNSTON ISLAND

FIG. 1 GEOMETRIC APPLICATIONS

15-5 LCURACAO TRINIDAD

PARAMARIBO

NATAL

FIG 2. SOUTH AMERICA DENSIFICATION

15-6 SATELLITE SEMIMAJOR ECCEN­ INCLI­ PERIGEE DATA NAME AXIS TRICITY NATION ARCS DAYS (C) DAYS (D) COUR IB 7473 km .017 28?3 1210 km 2 36 TRAN 4B 7415 .010 32.4 1105 2 36 VANG2 8307 .164 32.9 3267 3 54 BEACC 7512 .025 41.2 1310 5 36 54 ECHOR 7977 .010 47.2 1683 3 54 ANNA IB 7514 .007 50.1 1181 3 54 54 GEOSI 8079 .073 59.4 2279 3 36 54 TRAN 4A 7323 .008 66.8 1000 3 54 SECOR5 8165 .080 69.2 2421 1 18 1964 01A 7306 .004 69.7 931 3 54 BEACB 7367 .012 79.7 1078 3 36 18 1966 05A 7422 .024 89.7 1214 2 30 63041 7477 .004 90.0 1120 3 54 MIDAS 10008 .012 95.9 3750 2 36 GEOS II 7708 .032 105.8 1576 3 54 DATA TOTALS 41 444 378 TOTAL OBSERVATIONS: TRACKING STATIONS: C = CAMERA = 9822 BAKER-NUNN = 13 D = DOPPLER = 76795 DOPPLER =31 86617 47 FIG. 3 SATELLITE ORBITAL DATA

Figure 4 Baker-Nunn and Dopplgr TRANET Stations In ACIC gravitational Model Normal Matrices

15-7 FIGURES. GRAVITY DATA FOR l°xl°MEAN ANOMALIES CASE I CASE II STATION A0 AA AH STATION A

BELTSVILLE -0.1 -0.1 0.0 BELTSVILLE -0.1 -0.1 0.0 HOMESTEAD -0.0 -0.1 0.0 HOMESTEAD -0.0 -0.1 0.0 COLUMBUS -0.3 -2.6 -1.8 COLUMBUS -0.5 -2.0 -0.7 GREENVILLE -2.3 -3.6 -0.1 GREENVILLE -2.3 -1.2 0.8 CHANDLER -1.6 -4.8 -0.9 CHANDLER -1.9 -0.9 -1.7 BROWNSVILLE -3.6 -1.3 -2.7 BROWNSVILLE -3.6 -0.3 -2.7 FE WARREN AFB 0.7 -1.7 -0.9 FE WARREN AFB -1.1 -0.5 1.9 ALBUQUERQUE -0.1 -0.1 0.0 ALBUQUERQUE -0.1 -0.1 0.0

CASE IV STATION AH STATION AA AH

BELTSVILLE -0.1 -0.1 0.0 BELTSVILLE -0.1 -0.1 0.0 HOMESTEAD -0.0 - 0.1 0.0 HOMESTEAD -0.0 -0.1 0.0 COLUMBUS 0.0 -11.8 1.7 COLUMBUS 0.1 -26.9 5.9 GREENVILLE -2.1 -10.5 6.9 GREENVILLE -2.1 -25.9 14.8 -2.8 CHANDLER -2.1 6.6 CHANDLER -3.4 -11.4 19.4 BROWNSVILLE -2.5 -0.5 6.6 BROWNSVILLE -0.5 - 5.4 14.3 FE WARREN AFB 1.6 3.7 2.6 FE WARREN AFB 2.0 -9.4 10.3 ALBUQUERQUE -0.1 -0.1 0.0 ALBUQUERQUE -0.1 -0.1 0.0 FIG. 6 SHORT ARC TEST RESULTS (VALUES IN METERS)

15-8

1.4 1.4

1.4 1.4

0.8 0.8

0.2

-0.6 -0.6

AH

1.4

0.3 0.3

0.6

-1.8

-0.4 -0.4

AX AX

II

1.1 1.1

0.4 0.4

A A

0.8 0.8

0.2 0.2

0.9

0.9

2.6

2.7

-0.5

-2.2

CASE CASE

AH

AFB

RESULTS

3.1

1.2

0.7

STATION

-1.3

-4.8

WARREN WARREN

AX AX

BROWNSVILLE BROWNSVILLE

FE FE

GREENVILLE GREENVILLE

COLUMBUS COLUMBUS

CHANDLER CHANDLER

TEST

III

1.5

1.2

0.9

0.7

•0.3

METERS)

A A

IN IN

ARC ARC

0.5

0.7

0.5

0.4

0.6

CASE CASE

AFB

AH

(VALUES (VALUES

0.0

STATION

-0.2

-0.1

-0.2

-0.1

WARREN WARREN

AX AX

BROWNSVILLE BROWNSVILLE

COLUMBUS COLUMBUS

GREENVILLE GREENVILLE

FE FE

CHANDLER CHANDLER

LONG LONG

I

0.8

0.9

0.8

0.9

0.8

A0 A0

7 7

CASE CASE

AFB

FIG. FIG.

STATION

WARREN WARREN

BROWNSVILLE BROWNSVILLE

FE FE

GREENVILLE GREENVILLE

CHANDLER CHANDLER

COLUMBUS COLUMBUS

1

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