Improvement in the geopotential derived from satellite and surface data (GEM 7 and 8)

Abstract

A refinement has been obtained in the earth's gravitational field using satellite and surface data. In addition to amore complete treatment of data previously employed on 27 satellites, the new satellite solution (Goddard Earth Model 7) includes 64, 000 laser measurements taken on 7 satellites during the international satellite geodesy experiment (ISAGEX) program. GEM 7, containing 400 harmonic terms, is complete through degree and order 16. The companion solution GEM 8 combines the same satellite data as in GEM 7 with surface gravimetry over 39% of the earth. GEM 8 is complete to degree and order 25. Extensive tests on data independent of the solution shows that the undulations of the geoidal surface computed by GEM 7 has an accuracy (for commission errors only) of about 3 m (rms). The overall accuracy of the geoid estimated by GEM 8 (including short wavelength components not in the solution) is estimated f ) be about 4-1/4m (rms), an improvement of almost 1 m over previous solutions. The new combination solution is the first to show signs of "convection rolls" in the upper mantle below the Pacific Ocean.