Wavelet dispersion caused by frequency-dependent attenuation is a
common occurrence in ground-penetrating radar (GPR) data, and is
displayed in the radar image as a characteristic "blurriness" that
increases with depth. Correcting for wavelet dispersion is an important
step that should be performed before GPR data are used for either
qualitative interpretation or the quantitative determination of subsurface
electrical properties. Over the bandwidth of a GPR wavelet, the attenuation
of electromagnetic waves in many geological materials is approximately
linear with frequency. As a result, the change in shape of a radar
pulse as it propagates through these materials can be well described
using one parameter, Q*, related to the slope of the linear region.
Assuming that all subsurface materials can be characterized by some
Q* value, the problem of estimating and correcting for wavelet dispersion
becomes one of determining Q* in the subsurface and deconvolving
its effects using an inverse-Q filter. We present a method for the
estimation of subsurface Q* from reflection GPR data based on a technique
developed for seismic attenuation tomography. Essentially, Q* is
computed from the downshift in the dominant frequency of the GPR
signal with time. Once Q* has been obtained, we propose a damped-least-squares
inverse-Q filtering scheme based on a causal, linear model for constant-Q
wave propagation as a means of removing wavelet dispersion. Tests
on synthetic and field data indicate that these steps can be very
effective at enhancing the resolution of the GPR image.