Frequency-dependent attenuation analysis of ground-penetrating radar data

I investigate the frequency dependence of attenuation and problems with measuring the intrinsic attenuation in reflection data. It is well established that in many materials attenuation is approximately linear with frequency over the bandwidth of the GPR signal, with a slope characterized by a constant Q* parameter. I show the relationship of Q* to the parameters describing Cole-Cole relaxation and that when the dominant GPR frequency is well above or below the primary relaxation frequency, Q* is a simple function of the ratio of real to imaginary parts of the dielectric permittivity. However, near the relaxation frequency, a more complicated function is required to describe the slope of the attenuation curve. For some materials relaxation occurs in the range from 10 - 200 MHz which is in the primary range that GPR operates for many applications. Adding to this complication is the often overlooked problem of frequency dependent reflection which can be significant in typical field conditions. Despite these complications, frequency dependent attenuation analysis of reflection data can provide valuable subsurface information. In two field examples I demonstrate that frequency-dependent attenuation analysis can locate anomalies associated with non-aqueous phase liquid contaminants.