The Development of Geometric Satellite Triangulation and Field

The Development of Geometric Satellite Triangulation and Field

The Development of Geometric Satellite ~riangulationand Field Operations HERE HAVE BEEN numerous papers presented at for portable camera systems to be submitted for the T the meetings of, or in the publications of, the 1961 budget. American Congress on Surveying and Mapping and Mr. Harris of the Photogrammetry Research the American Society of Photogrammetry and many Branch did the research to determine the camera other engineering and scientific organizations, most suited for photographing both flashing-light dealing with some particular aspect of satellite trian- and sun-illuminated satellites, using the chopping gulation. In 1963 there were papers dealing with technique for satellite and star imagery. He, with the accuracy, calibration, and logistics of the por- the invaluable help of Mr. Ralph E. A. Putnam, the table camera system planned and designed by the electronic system designer who designed the Bal- Coast and Geodetic Survey, now the National listic Research Laboratories' missile tracking elec- Ocean Survey of NOAA. Since then there have been tronic system, wrote the specifications for mobile papers comparing satellite and geodetic triangula- timing and synchronization units; i. e., the original tion, and on world datum and related continental electronic package for the BC-4 system. networks. The specifications for the purchase of the camera All of these papers have dealt with what was were completed in September of 1960; and the planned and anticipated; accuracies and logistical specifications for the C&GS camera modification and support, or calling attention to the effects such a shutter, capping shutter control, which would en- completed world satellite triangulation network able the synchronization of the camera shutters with might have on the conventional continental and standard radio time signals (wwv) within *300 mi- small independent geodetic nets. croseconds, were completed in May 1961. Jack Davidson thought it might be interesting to Our personnel continued to study the BC-4 op- many to give a rather short summary of what ac- erations using different satellites at the Research tually happened in making passive satellite trian- Laboratories. In October 1961 a C&GS field party gulation a going program. In 1957 geometric satel- was for the first time located at the BRL, with Com- lite triangulation was unknown. But in January of mander Eugene A. Taylor as chief. He was charged that year three of us-William D. Harris', G. C. to become the expert on the total BC-4 field oper- Tewinke12, and myself-visited Dr. Hellmut ation, i.e., he was given the responsibility of Schmid at the Ballistic Research Laboratories, Ab- training the new personnel assigned to his party and erdeen Proving Ground. We were there to make for making the field equipment operational in any the necessary arrangements for these and other em- climate, completely self-sufficient, and fully por- ployees from the Division of Geodesy to visit and table for any mode of transportation (Figure 1). work with Dr. Schmid; to learn his methods of an- Those first assigned to his party of a period of alytic aerotriangulation as he applied this photo- months were LCDR Austin Yeager and Messers. grammetric technique to ballistic tracking. This Guy Fisher, Robert Price, Dick Fallgren, Dee group included Dr. Charles Whitten2, the chief of Kimble, Larry Schenkat, and Jack Fried. However, the Computing Division, and mathematicians such he called upon assistance from such people as Dick as Messers, Wallace Blackwell and Erwin Schmidt Ross from the Electronics Branch; John Smith, and Miss Rosemary Riordin. Chief of the Photographic Lab of Div. of Photo- In December of 1957 and January of 1958 the grammetry; Charles Theurer, Chief of Photogram- Russians launched Sputnik I and 11. These satellites metry Branch; and Ray Puhl of the same branch. In were photographed at Aberdeen and also their sat- January 1962 the C~GSreceived its first modified ellite trails were chopped. This work aroused our camera and electronics timing and synchronization interest in determining geodetic positions by pho- system. tographing a passive (sun-illuminated) satellite si- Echo I was launched on 31 October 1962; and on multaneously with three cameras at different known 2 November 1962, we were fortunate to photograph positions. Discussions with Dr. Schmid led us to the the flashing lights that were triggered manually at conclusion that with extreme care in design and op- an altitude of 1,000 km. eration of the cameras, timing, and plate measuring Taylor wrote, with the assistance of some of the systems, an accuracy of 1 part in 250,000 could be above personnel, the first Satellite Triangulation expected from the application of ballistic tracking Manual. As cameras and equipment were to be techniques for geodetic triangulation through the identical, it was necessary to use the same identical use of artificial Earth satellites. procedures of operation. By September of 1959 the Director of the Coast He, with the assistance of the U.S. Naval Obser- and Geodetic Survey had approved cost estimates vatory, Washington, D.C., solved the original basic PHOTOGRAMMETRICENGINEERING AND REMOTESENSING, 0099-1 112/84/5009-1333$02.25/0 Vol. 50, No. 9, September 1984, pp. 1333-1340. O 1984 American Society of Photogralnmetry PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1984 FIG.1. Setup for transporting the complete equipment for satellite tracking. problem in geometrical satellite geodesy programs, During 1962 we were refining the total camera that is, to record accurately time-correlated satellite system and assuring its mobility for all climates and and star images on photographic plates. We used a conditions. In the meantime the Photogrammetry fixed-camera approach, that is, the camera is fixed Division had been testing the accuracy of measuring in orientation during the entire observational pe- images on photographic plates with a stereocom- riod. Accurately timed shutters interrupt the star parator, an autograph, and monocomparator. After and satellite trails as they cross the camera's field of exhaustive tests it was determined by Mr. Frank view. The result is a photogrammetric record con- Lampton that the monocomparator was slightly sisting, on an average, of 700 star and 300 satellite more accurate than the regular photogrammetric images across the plate (Figure 2). The shutters that stereo instruments, and also better adapted to the produce the satellite images must be referred to a measurement of images on star and satellite plates. time standard to all the other camera systems in- At the suggestion of Mr. Harris we began improving volved in the simultaneous observation. In the be- the monocomparators by making them binocular ginning this precise transfer of epoch time was ef- viewing monocularly. We were also improving our fected by using portable crystal clocks, which were measuring and processing techniques and calibra- hand-carried, never shipped or checked as baggage. tion of the instruments. If necessary, an additional seat was paid for on The Coast and Geodetic Survey's first objective planes and the camera was strapped in a seat along- was to strengthen the North American Datum. The side the person carrying the clock. The same care original program was modest. It included the 48 was taken regardless of the mode of transportation. states and Alaska, via Canada. But the test of the This was replaced by a portable cesium clock which accuracy of a satellite triangulation was to be made was given the same care. at home first, on a 1500 km triangle with stations In 1964 or 65, Lt. George M. Cole, C&GS, was located in Maryland, Minnesota, and Mississippi. A one of several who carried these clocks from station fourth station, in Florida, was added to form a to station for synchronization reset. While transfer- second triangle. All stations were located on or tied ring time, he found there was a signal on Doppler to first-order triangulation stations. Observations that was as accurate without having to filter out data were made on the Echo I satellite, which ranged in or information. Because Johns Hopkins University altitude from 1300 to 1900 km. In processing and Laboratory was the one that worked on the devel- evaluating, the standard error of unit weight of the opment and refinement of Doppler, we went to plate measdrements after adjustment was 20.3 mi- them directly and asked if they could develop an crometres. This was a measure of precision of the instrument for us to utilize this signal. They agreed, photogrammetric process. The absolute accuracy of and an accurate and operational instrument was de- the photographic measurements was better than livered to us. We then contracted with an electrical '0.6 micrometres, or better than 1 part in 500,000. firm in the instrument business to build ten such The calibrations and comparisons we made with our instruments. These instruments were used in the 1st order network indicated that we consistently ob- Atlantic and Pacific Oceans and Antarctica for time tained accuracies of at least 1 part in 500,000 (all reset capability, utilizing polar orbit Doppler. They accuracy figures given are standard errors). proved very effective and accurate. They also solved Because of these accuracies, we were requested a problem of time we had not solved because of by the Defense Intelligence Agency (DIA) to locate Antigua and Bermuda. We readily agreed, pro- SATELLITE TRIANGULATION AND FIELD OPERATIONS background. viding they furnished the logistics and expenses in- the distances measured with the same, if not volved, as these islands were not a part of our plans greater, accuracy. to reach Alaska. The manufacturer of the Geodimeter was re- At this time it was realized we needed to start quested to make similar instruments for us, using the measurements of long accurate Baselines, such our instrument as a model. We were told that, be- as Florida to Maryland, Maryland to Minnesota, cause the C&GS was the only outfit in the world in- west from Florida to Mississippi, etc.

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