Verification and topographic correction of GPR data in three dimensions
Two sites in a Roman town allowed a direct comparison between GPR interpretation and excavation results in three dimensions. All the reflection features mapped by the geophysical survey were identified in the subsequent archaeological excavation. Some of these anomalies were shown to be walls preserved as a single layer of stone or completely robbed out. However, a number of walls that were later excavated were either not detected at all by the GPR or not imaged to their full depth. The reason for this is the limited penetration depth of the radar energy due to attenuation, which can be visually estimated from the data. In addition, the presentation of the GPR results was enhanced when the depth information was coded into the map of the interpretation. Finally a new processing step called topographic correction was developed to compensate for the antenna tilt and elevation in three dimensions. The differences and advantages of this method compared to 2D tilt corrections are discussed. Apart from migration, this topographic correction significantly improves the geometrical 3D accuracy and interpretation of the GPR data.