2-D ray-based tomography for velocity, layer shape, and attenuation from GPR data

Tomographic inversion for near-surface structure from multioffset ground-pe netrating radar (GPR) reflection data is implemented. The model is paramete rized as layers with constant velocity and constant attenuation. The soluti on is divided into two parts. First, the velocity and shape of each layer a re estimated from the observed reflection traveltimes; then using this geom etry and the corresponding ray paths, the attenuation of each layer is esti mated from the observed relative amplitudes. Solution of both tomographic p roblems is performed by singular value decomposition of the sensitivity mat rix (to compute information density, resolution, and covariance matrices as well as the solution). Tests on synthetic data, for which the solution is known, show that the algorithm converges efficiently to the neighborhood of the correct solution. Inversion of multichannel field data in a GPR line f rom a fluvial/eolian environment produces a model that is consistent with s tructural images and velocity estimates obtained independently by tradition al common-midpoint processing.