Waveform-based tomographic imaging of crosshole georadar data is a
powerful method to investigate the shallow subsurface because of
its ability to provide images of electrical properties in near-surface
environments with unprecedented spatial resolution. A critical issue
with waveform inversion is the a priori unknown source signal. Indeed,
the estimation of the source pulse is notoriously difficult but essential
for the effective application of this method. Here, we explore the
viability and robustness of a recently proposed deconvolution-based
procedure to estimate the source pulse during waveform inversion
of crosshole georadar data, where changes in wavelet shape with location
as a result of varying near-field conditions and differences in antenna
coupling may be significant. Specifically, we examine whether a single,
average estimated source current function can adequately represent
the pulses radiated at all transmitter locations during a crosshole
georadar survey, or whether a separate source wavelet estimation
should be performed for each transmitter gather. Tests with synthetic
and field data indicate that remarkably good tomographic reconstructions
can be obtained using a single estimated source pulse when moderate
to strong variability exists in the true source signal with antenna
location. Only in the case of very strong variability in the true
source pulse are tomographic reconstructions clearly improved by
estimating a different source wavelet for each transmitter location.