Why cannot LASERTC correct for the effect of terrain at large distances?
LASERTC is inherently designed to correct for terrain very close to a gravity station, using irregularly-distributed elevation data supplied by the user. To achieve such accuracy, a smooth surface is fitted to the elevation data supplied by the user; the surface is then numerically integrated using an adaptive numerical integration scheme. The main reason that LASERTC cannot calculate corrections for distant terrain is that the number of terrain samples that the surface-fitting procedure can accommodate is limited. For example, to correct for terrain at distances > 1000 m, a supplementary terrain correction procedure should be used (INNERTC or RASTERTC).
