Terrain correction computations for a densely sampled DTM in the Bavarian Alps

Abstract.

 Various methods are presented for terrain correction computations referred to a digital terrain model (DTM) of a part of the Bavarian Alps to the southwest of Munich. The most commonly used fast Fourier transform (FFT) techniques exhibit some shortcomings for the zone adjacent to the computation point. A combination method is proposed which applies FFT for the whole DTM except for a small zone surrounding the computation point. In the latter an analytical method is employed by decomposing the terrain into elementary bodies. Different modelling techniques are tested, with the arbitrary polyhedron being the most precise one. With the proposed method both the exactness of the analytical expressions and the efficiency and speed of the FFT technique can be exploited. It is shown that this modified approach has two positive effects. First, the convergence of the FFT series is regained, which is not always the case when slopes greater than 45^∘ exist in the terrain. Second, it approximates the terrain correction as computed by the classical prism summation method better than its linear approximation as given by FFT.