free/free waveguide
R O B F
190.0 0                         src freq
4                              nb of layers
  0    0 0 0    0     0   0   #1 (upper half space)
  0 1500 0 0 -888.888    1.0 0   #2
-1.50
 60 1500 0 0    0     1.0 0
200    0 0 0    0     0   0   #4
65                             src depth
0.2 199.8 500                  rcv depths
1200 1e8                       cmin cmax
2048 1 2048 1024                k integration parameters
8192 180.0 200.0 0.002 4 .1  1    time, freq & range param.