The Development by the National Imagery and Mapping Agency of a Global Surface Gravity Anomaly Database for the EGM96 Geopotential Model and Future Applications

Abstract

The National Imagery and Mapping Agency (NIMA) gravity contribution to worldwide geodetic modeling is substantial. NIMA along with NASA/Goddard Space Flight Center (GSFC) have produced a global set of 30′ × 30′ and 1° × 1° surface mean free-air gravity anomalies in support of the EGM96 geopotential model development. The extensive data archive at NIMA is the main source of gravity information from which the 30′ and 1° mean values were estimated. New terrestrial sources of gravity data used in the model include the former Soviet Union, Greenland, South America, Africa, Southeast Asia, Antarctica, and the Arctic. Improvements to current terrestrial sources have been made in North America, Europe, and Australia. Substantial effort was made to ensure accurate and consistent processing of the point gravity anomaly data used in the estimation of the 30′ and 1° mean values. The mean values and their accuracies are estimated using least-squares collocation (LSC) and remove-restore techniques implemented at NIMA. For the reduction process, consistent 1′ and 5′ elevation databases were compiled by NIMA and GSFC using the best worldwide elevation sources currently available. In the future, NIMA will continue its worldwide data acquisition attempts to improve its point gravity anomaly database. These improvements, along with enhancements in gravity modeling techniques, will benefit worldwide geoid models, navigation systems, and mapping capabilities.