Since the last Quadrennial Report in 1967, progress in satellite geodesy has been confined to refining the results as of 1967 by adding data of greater accuracy and better distribution and to combining the various solutions. None of the avant-garde methods, such as satellite, altimetry, very long base line interferometry (VLBI), drag-free satellites, or satellite-to-satellite tracking with continuous coverage, has produced results at this time. Other representations of the gravity field, such as a layer model [Koch and Morrison, 1970] and gravity anomalies estimated from satellite data [Obenson, 1970], have been successful and show promise. Several studies [e.g., Wong and Prislin, 1970] have shown that electronic (Tranet Doppler) data and optical (Baker-Nunn) data are quite compatible and equivalent for orbit calculation purposes. This compatibility indicates that either type of data can be used for geodetic research.
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