FREQUENCY-DOMAIN MIGRATION FOR SUBSURFACE RADAR CONSIDERING VARIATIONS IN PROPAGATION VELOCITY

The techniques for imaging optically opaque region using an electromagnetic wave radar are being developed. One important application of these techniques is the detection of buried pipes and cables. The image quality of subsurface radar often becomes low because the electromagnetic waves are affected by the attenuation and inhomogeneity of soil. Hence, a method which improves the quality of the radar images has been required. The migration method is utilized in reflective seismic processing and is derived based on the solution of the wave equation represented in spatial frequency domain. It is classified into the F-K and the phase-shift (P-S) migration method. The former is derived on the assumption that propagation velocity of the wave is uniform in the soil while the latter is assumed that the propagation velocity is varying depending on the depth from the ground surface. The P-S method gives relatively good quality images but it requires very long computation time. In this paper, we propose the block migration method in which the F-K method is applied to the divided image blocks with local propagation velocity. In order to solve a problem concerning the connection between the contiguous blocks we present two approaches which are the processings using the overlapped regions and the Lapped Orthogonal Transform (LOT). Some experimental results point out that the block migration, method has a good capability of improving the image quality and the processing time using LOT becomes one tenth in comparison with the P-S method.