Applications Of Multi-Offset Ground Penetrating Radar

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