Radar Tomography For Cavities Detection

Preliminary tests on laboratory models have enabled us to provide some guidelines for traveltime ray<br>tomography with GPR applied to civil engineering problems, specifically to find voids in pillars, walls and<br>structures. The width of the Fresnel zone and the source and receiver locations are the limits to resolution<br>capability. For crosshole geometry a criterion to know resolution capability, based on detectable wavenumbers,<br>is analytically derived.<br>Acquisition and reconstruction parameters (source and receiver location, operating frequency, measurement<br>number, acquisition time, slowness grid) are discussed and optimized with tomographic experiments on some<br>models drilled expressly to produce voids. Tomography is solved by SVD, experimenting both regular and<br>irregular gridding. An iterative procedure for noise reduction is proposed to improve the solution. A sort of<br>black and white tomography is also applied to explore the actual limits of straight ray approximation. For<br>crosshole geometry a wavenumber decomposition of the problem is proposed and the benefits discussed.