FFTTC

A program to compute gravimetric terrain corrections using the Fast Fourier Method

A program to compute gravimetric terrain corrections using the Fast Fourier Method

TerrainCorrectionGrid=FFTTC(filename,minlat,maxlat,minlong,maxlong,res,sphericalCap,outfile,PadS,PadN,PadW,PadE)

The program reads in esri ascii digital elevation model (DEM) data files given by the input variable 'filename'. The latitude and longitude extents of the gird and the grid resolution are input by the variables 'minlat', 'maxlat', 'minlong', 'maxlong' and 'res', all in degrees.

A maximum radius to evaluate the terrain correction out to (from the computation point) is specified by 'sphericalCap' and zero padding is applied by specifying the padding extents to the South, North, West and East in degrees by 'PadS', 'PadN', 'PadW' and 'PadE'. The padding attempts to minimize the effect of cyclic convolutions of the in the Fourier domain.

The output is a grid of terrain corrections, one for each latitude and longitude location in the input DEM file. These are written to an output file specified by the variable 'outfile'.

N.B. this formula is not valid for terrain with gradients steeper than 45 degrees, and there will be edge effects. Using overlapping digital elevation model tiles is recommended for large areas to avoid edge effects.