The accuracy of geopotential models

The accuracy of two recent geopotential models, GEM 7 and GEM 8, is evaluated and is found to be about 4.3 m with respect to the global geoid surface for GEM 7 and 3.9 m for GEM 8. The accuracies are root mean square values obtained by the use of 400 coefficients for GEM 7 and 706 coefficients for GEM 8. Independent observations used in the evaluation include 159 lumped coefficients from 35 resonant orbits, two sets of fields derived from optical-only and laser-only data, sets of zonal and resonant coefficients, and geoid undulations. The ratio of estimated commission to formal error in GEM 7 and GEM 8 ranges from 2 to 5. Several other recent geopotential models are examined.