Dynamic satellite geodesy

Since the last report (Gaposchkin, 1975) dynamic satellite geodesy has continued to develop and refine its capability to determine locations on the earth's surface and to improve our knowledge of the global gravity field (Anderle 1975, 1978, 1978a; Gaposchkin 1977, 1979; Lerch, et al., 1977, 1978a;Smith, et al., 1976, 1978;Wagner, et al., 1977). The launching of two spacecraft, GEOS‐3 and Lageos (Laser Geodynamics Satellite) in 1975 and 1976 respectively, are having a profound impact on satellite geodesy. GEOS‐3 provided the first real opportunity to test two new techniques, satellite altimetry and satellite‐to‐ satellite tracking, Altimetry is the measure of the distance between the satellite and the ocean surface and the technique requires a comparable knowledge of the spacecraft motion to the precision of the altimeter. For GEOS‐3 the altimeter had a capability of a few decimeters and a similar accuracy in orbit determination required a significant improvement in all areas, tracking, computation, gravity field modeling, etc.