Elevation values are negative, since they are above land surface. The first number in the file is nsurf, the number of nodes defining the topography. The lines following nsurf contain (xsurf, zsurf) pairs defining the the topography. The program interpolates the missing nodes from the input data.

The remaining parameters, the velocity reduction factor and the air speed, are defined in the parameter file:
v_reduce, the velocity reduction factor above the topographic surface. This factor is less than 1.0.
airspeed, the speed of sound in air.
See the description of these parameters in the main PRONTO documentation.

An example topography input file follows:

19
0.00 -2.50
0.50 -2.40
1.00 -2.30
1.50 -2.30
2.00 -2.30
2.50 -2.40
3.00 -2.40
3.50 -2.40
4.00 -2.50
4.50 -2.50
5.00 -2.50
5.50 -2.40
6.00 -2.40
6.50 -2.30
7.00 -2.40
7.50 -2.40
8.00 -2.30
8.50 -2.40
9.00 -2.40