Frequency Dependence of Attenuation in Ground-Penetrating Radar: Insights from the Bishop Tuff

Total attenuation in ground-penetrating radar (GPR) was directly measured in radargrams of the Bishop Tuff, CA, from 12.5–200 MHz. The weak variation of attenuation with frequency reaffirms the "GPR Plateau" concept and argues against a constant-Q model. Electrolytic absorption —determined using collocated DC resistivity profiling/ sounding—accounts for about half of the attenuation and is by definition independent of frequency. The radargrams contain numerous reflections interpreted to be subvertical and subhorizontal cooling and unloading joints, suggesting that scattering is the other major contributor to attenuation. The residual attenuation after subtraction of absorption is attributed to scattering: significant variations in scattering attenuation are restricted to the decade around 30 MHz and are well fit by a Born scattering model.