Most ground-penetrating radar suveys are acquired in quasi zero-offset
mode, Le. source-receiver offsets are small compared to the target
depth. The correct way to realistically model such an experiment
would be to compute a corresponding sequence of common-offset radargrarns.
In finite-difference time domain (FDTD) modeling this approach would
be excessively expensive and hence is substituted by initiating a
downward travelling plane wave at the earth's surface. However, this
method of zero-offset modeling is only realistic for horizontafly
layered, one-dimensional media, and thus is unsatisfactory in most
realistic situations and defeats the very purpose of finite-difference
rnodeling. Therefore, we propose an alternative approach based on
the "exploding reflector" concept. This approximation is more realistic,
even in highly complex media, and is only marginaily more expensive
than the plane wave method.