Improved gravimetric terrain corrections

objective of this paper is t o improve gravimetric terrain corrections by: (1) investigating the effect of different topographic representations that are suitable for efficient processing of high volumes of data (e.g. the mass prism and the mass line models) on terrain corrections and on geiod computations; (2) accelerating the convergence of fast Fourier transform (FIT)-based terrain-correction formulae; and ( 3) developing a set of new formulae corresponding to the mass prism topographic model, which can be evaluated efficiently with the 2-D FIT. Terrain corrections were computed on a grid of 600 by 600 points with spacing 30 ” by 6 0 in the Rocky Mountains of British Columbia, Canada. The effect of using the mass line model instead of the mass prism model is 7.4mGal (maximum) and 0.7 mGal (rms) on the terrain corrections, and 24 cm (maximum) and 16 cm (rms) on the geoid undulations. The optimizations made on the FFT-based terrain-correction formulae effectively speed up the convergence. The newly developed mass prism terrain-correction formula significantly reduced the required computer time and provided identical results with those from the rigorous numerical integration. On an IBM/RISC machine running AIX, the computation of the 15 convolutions (the matrix size was expanded to 1200 by 1200 after 100 per cent zero-padding) via the new formulae only took 15 min (user time), while the numerical summation method required 83.5 days. Key words: digital topographic representation, geoid undulation, terrain correction.