Synthesis of amplitude‐versus‐offset variations in ground‐penetrating radar data

Abstract

To evaluate the importance of amplitude‐versus‐offset information in the interpretation of ground‐penetrating radar (GPR) data, GPR reflections are synthesized as a function of antenna separation using a 2.5-D finite‐difference solution of Maxwell’s equations. The conductivity, the complex dielectric permittivity, and the complex magnetic permeability are varied systematically in nine suites of horizontally layered models. The source used is a horizontal transverse‐electric dipole situated at the air‐earth interface. Cole‐Cole relaxation mechanisms define the frequency dependence of the media. Reflection magnitudes and their variations with antenna separation differ substantially, depending on the contrast in electromagnetic properties that caused the reflection. The spectral character of the dielectric and magnetic relaxations produces only second‐order variations in reflection coefficients compared with those associated with contrasts in permittivity, conductivity, and permeability, so they may not be separable even when they are detected. In typical earth materials, attenuation of propagating GPR waves is influenced most strongly by conductivity, followed by dielectric relaxation, followed by magnetic relaxation. A pervasive feature of the simulated responses is a locally high amplitude associated with the critical incident angle at the air‐earth interface in the antenna radiation pattern. Full wavefield simulations of two field data sets from a fluvial/eolian environment are able to reproduce the main amplitude behaviors observed in the data.