A Joint GSFC/DMA Project for Improving the Model of the Earth’s Gravitational Field
The U.S. Defense Mapping Agency and the NASA Goddard Space Flight Center with the aid of other organizations such as The Ohio State University are cooperating in a joint effort to determine a significantly improved degree 360 spherical harmonic model representing the Earth’s gravitational potential. This new model will be of immediate use in defining a geoid undulation model that will be the basis for an enhanced WGS84 geoid.
The development of the new model is driven, in part, by the need to determine an accurate geoid undulation model that will be the reference surface for a World Height System to be implemented in the 1996 time period. In addition, the new geoid estimation will help satisfy increasingly important studies in ocean circulation (sea surface topography) and geodetic positioning through GPS.
The new model estimation will incorporate existing and new satellite data. New data will include GPS tracking of Topex/Poseidon, Doris tracking of several satellites, altimeter data from Topex/Poseidon, and ERS-1 and Doppler data from satellites at inclinations not covered or weakly represented in previous solutions.
The surface gravity data to be used in the new solution will be based on an updated 30’ mean anomaly data base developed at the DMA Aerospace Center. This new data set will incorporate a substantial amount of new data that has, and will, become available in Europe, the FSU, South America, Greenland, Africa, Asia and Antarctica. Anomaly values in areas such as Canada, the United States and Australia will be based on updated data files. This data will be used, after suitable corrections, to form normal equations that can be used with the satellite derived normal equations.
In addition, 30’x30’ mean anomalies derived from the Geosat Geodetic Mission satellite altimeter data will be used in the project. The file will be merged with the files based on the surface terrestrial data. In areas where no data exists, anomaly estimates will be made from new elevation data through topographic isostatic models to ultimately yield a global 30’ anomaly file. In addition, an updated l°xl° anomaly file based on terrestrial data (both land and ocean) will be determined.
The final stage of the data processing will be the development of several degree 360 models using different data sets and weighting procedures. The current plan is to use existing software, for the combination solution, with minimum modifications to assure a timely effort. Several preliminary models will be made available to the international community for evaluation. A final model will be selected based on extensive tests of the preliminary models. The final model and accuracy estimates will be released in mid 1996. The model will be used to determine accurate geoid undulations that will be available in gridded form.
KeywordsGravity Anomaly Satellite Laser Range Bouguer Anomaly Altimeter Data Geoid Undulation
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