Soil electromagnetic mapping for enhanced GPR utility location

The geographical mapping of soil electromagnetic properties provides many advantages to utility location, including highlighting areas where soil properties cause significant signal loss, providing signal velocity predictions and estimating the smallest detectable feature in a survey. All of these factors can significantly improve the usefulness of utility location survey data. However, the mapping of soil electromagnetic properties is complex, and relies on many geotechnical and environmental variables. Also, higher frequency ground penetrating radar (GPR) equipment is required if the detection of small utilities is to be achieved, but this greatly limits the depth of signal penetration. Therefore, the wide signal bandwidth required to balance resolution and penetration results in a need to relate mapping parameters to complex frequency-dependent variations, water contents and temperatures. Mapping these properties over large geographical areas is fraught with difficulties, including the vast number of measurements required to achieve even the most basic geospatial resolution. However, geotechnical testing is widespread and can provide data for the prediction of soil electromagnetic properties. Therefore, Mapping the Underworld (MTU), a major UK research project attempting to significantly improve geophysical utility location, is exploring the possibility of using such data for selected urban mapping of GPR relevant soil properties.