Investigations into the utilization of passive satellite observational data
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Date
1968-06
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Publisher
Ohio State University. Division of Geodetic Science
Abstract
There are several organizations observing satellites for geodetic purposes. Satellites have provided an object at a finite distance which can be used to establish the spatial relationship between several ground stations. This relationship may be extended over much greater distances and is free of many limitations and errors inherent in the classical terrestrial methods of triangulation. It does present new problems of its own however. This report describes several methods of determining accurate satellite positions optically. Specifically, it deals with passive satellites recorded against the stellar background on the photographic plate of a metric camera. The trail of a passive satellite consisting of several hundred images on a photographic plate may be utilized for geodetic purposes in several ways: (1) All image coordinates may be fitted to a single polynomial with the time as argument and all the information on the plate is aggregated into a single highly precise fictitious satellite direction. This is the approach of the USCGS using the Wild BC-4 camera plates. (2) The image coordinates may be divided into 3-4 groups and a separate polynomial is fitted to each group. The information on the plate thus is aggregated into 3 - 5 fictitious satellite directions each somewhat less precise than the one in (1). The advantage of this method is that it is possible to deduce 3 -5 simultaneous observations even from single plates which may yield a solution for the directions between the stations involved. Method #(1) does not provide a solution from single plates. If this method is used, it may be possible to reduce the time which must be spent at each of the observation stations. (3) Each or selected (e.g., every twentieth) images may be reduced individually and used in the geodetic solution. In this case there will be as many simultaneous observations deduced from each pair of plates as many images were selected. The advantage of this method is the inexpensive plate reduction. It is estimated that to reduce one image costs about $15; thus for the maximum of 15 -20 images per plate the cost would be $225 - 300, which figure is much less than the amount required to reduce a plate with Method #(1). (4) The right ascension and declination of each image (this is the form in which for example the BC-4 data is deposited in the Data Center) may be used directly in the short-arc mode. The paper deals with the results obtained in the four modes mentioned above. The accuracy aspects of the four solutions are investigated.
Description
Prepared for National Aeronautics and Space Administration, Washington, D.C.: Contract No. NGR 36-008-093, OSURF Project No. 2514