Problems and Solutions with GPR Data Interpretation: Depolarization and Data Continuity

When interpreting large area ground-penetrating radar (GPR) surveys it has been found that the depolarization of electromagnetic waves affects the reflectivity of some subsurface features, which has a larger effect on detectability than previously thought. This depolarization can make some archaeological structures almost invisible using standard processing steps including reflection profiles and energy slice maps. Only recording data with orthogonal antenna orientation will eliminate this problem. After three-dimensional interpretation of three-dimensional volumes of GPR reflections a variable width gap between floors and their bounding walls has been repeatedly observed. This newly detected problem is clearly visible in a number of surveys conducted at a Roman town in Switzerland. It is explained by the distorted geometry of the sides of the floors common in the Roman Empire, resulting in a reflection surface that reflects most energy away from the surface antennae and only limited energy is recorded, making portions of the floors invisible. Copyright (C) 2011 John Wiley & Sons, Ltd.