Trace Modelling: A Quantitative Approach to the Interpretation of Ground Penetrating Radar Profiles

Classical analysis of radar profiles generally relies on a visual inspection and interpretation of profiles and sometimes on inverse modelling of the acquired data. Both methods suffer severe limitations due to the antenna resolution, thereby preventing the identification of tiny structures, especially in forensic applications. Here we describe a forward modelling technique, which allows to reproduce individual traces (A-scans) of radar profiles through superposition of Ricker wavelets. The method allows to detect ultra-thin layers, well beyond the Ricker and Rayleigh vertical resolution of GPR antennas. This approach starts from an estimation of the instrumental uncertainty of common monostatic antennas and takes into account of the frequency-dependent attenuation, which causes spectral shift of the dominant frequency acquired by the receiver antenna. The forward modelling procedure loads a single trace from a radar profile and allows to build a synthetic A-scan by fitting a sequence of Ricker wavelets with user-defined amplitude, polarity, and arrival time to the acquired trace. The resulting synthetic trace can be used to create a reflectivity diagram that plots reflection amplitudes and polarities versus depth. Often a reflectivity diagram shows intervals bounded by reflectors of opposite polarity, associated with layers having higher or lower velocity than the surrounding material, respectively. These intervals may result from very subtle features that represent interesting survey targets, for example buried bones, small cracks, thin lens of liquid contaminants, etc. and could be confused with individual reflectors through the simple visual inspection of a radar profile. Our quantitative approach can be used in several applications of GPR methods, especially in forensic, paleontological, civil engineering, heritage protection, and soil stratigraphy applications.