A GEODETIC APPROACH TO GRAVITY-DATA REDUCTION FOR GEOPHYSICS

The currently adopted approach to reduce observed gravity data for geo physical purposes includes several approximations. These were original ly used to reduce computational effort, but have remained standard pra ctice, even though the required computing power is now readily availab le. In contrast, more precise gravity reductions are routinely employe d in physical geodesy. The difference between simple Bouguer gravity a nomalies derived using the geophysical and geodetic approaches can rea ch several tens of mu m sec(-2). The geodetic reductions include a mor e accurate calculation of normal gravity as a function of latitude, an d a free air correction that accounts for the non-sphericity of the fi gure of the Earth. Also important, especially given the advent of Glob al Positioning System coordination of gravity surveys, is the need to ensure that the correct vertical and horizontal coordinate systems are used for the gravity reduction procedure. Errors associated with tie use of non-geocentric horizontal coordinates and ellipsoidal heights a re significant when compared with the accuracy of an individual gravit y measurement. A generalised gravity reduction program and a coordinat e transformation program are presented which can be employed to reduce geophysical data in a geodetic manner. (C) 1998 Elsevier Science Ltd.