GRIM gravity model improvement using LAGEOS (GRIM3‐L1)

Improved modeling of the earth's geopotential is one of the major tasks of satellite geodesy. The availability of a new set of precise LAGEOS satellite laser ranging (SLR) data as well as Seasat-acquired observations enabled us to compute an improved solution in the GRIM model series. The new geopotential GRIM3-L1 recombined the satellite perturbation normals of the former GRIM3 solution with new normal equation subsystems derived from an additional 16 months of LAGEOS SLR data, oceanic 1°×1° mean free air anomalies recovered from Seasat altimetry, an updated set of terrestrial 1°×1° mean free air anomalies, and several condition equations for zonal and resonant harmonics. The combined normal equations were solved for a complete set of spherical harmonics up to degree and order 36 and the coordinates of 109 tracking stations. Comparisons with altimetry-derived quantities, terrestrial gravity, anomalies from satellite-to-satellite tracking, longitude accelerations of 24-hour satellites, and satellite orbit fits show a substantial improvement over previous GRIM solutions and indicate that the LAGEOS data have contributed considerably to the reliable estimation of the long-wavelength portion of the gravity field.