Mean gravity anomalies from a combination of Apollo/ATS 6 and GEOS 3/ATS 6 SST Tracking Campaigns

Abstract

The satellite to satellite tracking (SST) technique has been used to measure the earth's gravity field. Data from the Apollo/Soyuz and GEOS 3 missions, obtained at greatly differing altitudes, have been used in combination to determine 5° and 10° equal area mean gravity anomalies in the South Atlantic and Indian Oceans and over the African continent. The Apollo/ATS 6 SST data consist of 47 passes of data taken from the 230‐km Apollo altitude, while the GEOS 3/ATS 6 data set consists of 45 passes taken from 840‐km altitude. Through a combination of the two data sets with the GEOS 3 SST data providing stability for the solution at the longer wavelengths, excellent (5° at ±3 mgal, 10° ±1 mgal) results were obtained for this largely unsurveyed region. These results have been compared to an altimetric surface at comparable wavelengths, providing good agreement (±1 mgal for 10° blocks and ±5 mgal for 5° blocks) between these independent measuring techniques. The terrestrial data over the African continent is shown to differ significantly (rms difference of 8 mgals with a maximum difference of 23 mgals) from a comparison of 10° GEOS 3 SST derived blocks. A simulation has also been performed to assess the data requirements, aliasing, and noise characteristics of a low spacecraft being tracked in a high‐low SST configuration. The results of the simulation were employed in the design of the SST data reduction procedures.