Amplitude and phase variation with offset (APVO) analysis of ground penetrating radar data

Amplitude and phase variation with offset (APVO) analysis of ground penetrating radar (GPR) data can improve the differentiation of non-aqueous phase liquid (NAPL) from stratigraphic changes. Previous controlled experiments have shown that common offset (CO) GPR methods can detect the presence of NAPL in soil by examining amplitude, diffraction, and travel time (velocity) anomalies. Unfortunately, stratigraphic changes (such as the presence of a silt or clay lens) or perched water table may produce similar amplitude and velocity anomalies. Therefore, it is difficult to delineate NAPL in a region with unknown stratigraphy exclusively using CO GPR data collection methods.; Forward models based on the Fresnel equations predict that amplitude responses exist at various incidence angles that will allow for differentiating NAPL from hydrogeologic changes. Models generated as part of this research indicate that collecting and comparing the amplitude responses from linearly polarized electric field vertically oriented (EV) to the horizontally oriented (EH) at various incidence angles improves target discrimination.; The results of five field tests are presented that demonstrate the chronological methodology involved in developing the APVO/GPR technique. These results indicated that collecting common-midpoint (CMP) GPR data using EH and EV polarized signals at anomalous CO amplitude responses can improve the detection and differentiation of NAPL from stratigraphic changes in the subsurface. The field test results from the final site are corroborated using capacitively coupled resisitivity data and intrusive sampling.