TERRAIN CORRECTION PROGRAM FOR REGIONAL GRAVITY SURVEYS

An algorithm is presented for the computation of gravity terrain corre ctions from a digitized grid representing topography. Different approx imations for topography at various distances from the gravity station are used to make the computation more efficient. For the distant zone (30 < r < 50 km) topography is approximated using a vertical line mass distribution. In the intermediate zone (2 < r < 30 km) a segment of a hollow vertical cylinder is used. The near zone (0.5 < r < 2 km) is a pproximated using vertical rectangular prisms with sloping upper faces . A new method is used to compute the correction for the inner zone wh ich is the digitized square where the gravity station is located. The gravity effect of topography in the inner zone is calculated from four triangular prisms with vertices made of the station location and the comers of the square. The computer program has been tested comprehensi vely with a regional gravity database from the Southern Uplands of Sco tland in which all terrain corrections were carried out originally usi ng the Hammer chart method.