A Preliminary Gravitational Model to Degree 2160

Abstract

The National Geospatial-Intelligence Agency (NGA) of the USA has embarked upon the development of a new Earth Gravitational Model (EGM), to support future realizations of NGA’s World Geodetic System. Current plans call for the development of the new EGM (EGM05) by the end of 2005. The new model will be complete to degree and order 2160, and aims at a ±15 cm global Root Mean Square (RMS) geoid undulation error requirement. The new model will combine optimally the gravitational information that is extracted from dedicated geopotential mapping satellite missions (CHAMP, GRACE), with the information contained within a global gravity anomaly database of 5′×5′ resolution. This paper describes the development of a Preliminary Gravitational Model (PGM2004 A). We developed PGM2004A by combining the GRACE-only model GGM02S, with a 5′×5′ global gravity anomaly database compiled by NGA. PGM2004A is complete to degree and order 2160, and is accompanied by propagated error maps at 5′×5′ resolution, accounting for the entire bandwidth of the model (from degree 2 to degree 2160), for various model-derived gravimetric quantities (Δg, N, ξ, η). We have evaluated PGM2004A through comparisons with independent data including GPS/Leveling data, astronomic deflections of the vertical over the conterminous US (CONUS), and altimeter data from TOPEX. The results of these comparisons indicate that the goal set for EGM05 is well within reach. We summarize in this paper our current status and technical accomplishments, and discuss briefly our next steps towards the development of EGM05.