These routines model tropospheric radiowave propagation over variable terrain and calculates propagation loss vs. height and range. Propagation loss is displayed in dB contours on a height vs. range plot. TPEM is based on the split-step Fourier PE method and was originally developed from an early PE model called PEPC, written by Fred Tappert. Propagation loss over variable terrain is modeled by shifting the field an appropriate number of bin widths correspondc ing to the height of the ground. The field is determined using the smooth earth PE method.-These routines model tropospheric radiowave propagation over variable terrain and calculates propagation loss vs. Height and range. Propagation loss is displayed in dB contours on a height vs. Range plot. TPEM is based on the split-step Fourier PE method and was originally developed from an early PE model called PEPC, written by Fred Tappert. Propagation loss over variable terrain is modeled by shifting the field an appropriate number of bin widths correspondc ing to the height of the ground. The field is determined using the smooth earth PE method.