Applications Of Multi-Offset Ground Penetrating Radar

Abstract

The estimation of propagation velocity is important for the correct processing and interpretation of ground penetrating radar (GPR) reflection data. Most, if not all, GPR surveys, are very limited in spatial extent and the common perception is that within the survey range, radar propagation velocity in the shallow subsurface has very slow or no lateral variation. Therefore, a single (1-D) velocity function is considered adequate to describe the subsurface. In this study it is shown that, in fact, lateral variation in radar velocity can be quite significant. An effective means of determining velocity is based on normal moveout velocity analysis of common midpoint multi-offset data. Applying this technique at many locations along a GPR survey provides a more accurate description of the actual 2-D velocity distribution. When the multi-offset acquisition geometry necessary for normal moveout velocity analysis is applied continuously in the GPR survey, an improved radar reflection image is attained by stacking traces at common midpoints. The 2-D normal moveout velocity description is used to make necessary adjustments to the data before the stack. The velocity analysis and common midpoint stack techniques are applied to an example of GPR data acquired using the multi-offset geometry at every survey station. The results show that reflection signal-to-noise and effective depth of penetration of stacked multi-offset data are improved, as compared to standard single-offset GPR data. It is also shown that, the stacked multi-offset data is itself improved as the number of velocity analysis locations is increased, up to some practical limit.