Thursday 25 August 2005

G2
1000-1155 hours

350
Geoid estimation in a coastal region: Corpus Christi, Texas, USA
Jeffress, Gary¹, Chen, Tianyou², Aiken, Carlos², Ferguson, John², Gutierrez, Roberto³
1 Texas A&M University-Corpus Christi, Corpus Christi, TX, USA
2 University of Texas at Dallas, TX, USA
3 University of Texas
Author email: jeffress@tamucc.edu
Geoid models are available at a national scale but their accuracy depends on both the parameterization and the availability of constraining data. The degree to which small scale features must be considered is a function of variations in topography and subsurface mass density heterogeneity. Improved higher sample density gravity data which is the basis of geoid modeling, could be used to define smaller scale geoidal undulations. Along the Texas Gulf Coast the topographic relief is very low and the gravity stations in the national database are spaced at ten kilometer or greater intervals with large gaps along the coast and in shallow water areas. The Free-air gravity however exhibits a steep gradient increasing offshore to the south. Would the inclusion of a better gravity station distribution significantly improve the orthometric height corrections in this area relative to existing geoid models? New gravity observations were made around Corpus Christi on the land and at oil well platforms in the bay and inland waterway using high performance gravity meters and carrier-phase rapid static GPS. A gravity database from historical, proprietary exploration gravity surveys by petroleum companies was made available and very significantly improved the station coverage and were tied and merged with the new observations through reprocessing. A geoid model was computed using methodology similar to that employed by the National Geodetic Survey to create the gravity based model G99SSS. Thirteen control points were established using both GPS and conventional first order leveling. The new CCGEOID model has a better fit to the control than either the G99SSS or GEOID99 models. This comparison is being extended to the new GEOID03 model. CCGEOID has 5 to 10 km wavelength features, which are not resolved by the older models. The improved gravity coverage in the coastal and near shore areas significantly improved the corrections.

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