The directory is used to compute a synthetic dataset for a
model with a horizontal recording surface, but a variable 
base of weathering.  The targets are three horizontal reflectors.
Shots are off-end with the first shot at 0 ft.  The shot spacing
and the group interval are 100 ft (the nearest offset is also 100 
ft.), and the final shot is at 20000 ft.  

To make synthetic data type:

Xcshot                    displays model and creates datafile

