Migration method for subsurface radar considering variation of propagation velocity in depth direction

Abstract

AbstractThere are two methods for improving the resolution in the scan axis direction of the subsurface radar, i.e., the F‐K migration method and the phase‐shift method. The resolution can be improved significantly by the F‐K migration method if the propagation velocity of the radio wave in the ground is uniform and by the phase‐shift method if the propagation speed varies in depth and is known. In general, the propagation speed of the radio wave often changes in depth and its distribution is unknown.In this paper, a method is proposed in which the radar image is divided in the depth direction and the propagation time difference up to the divided block is compensated for so that the F‐K migration method is applied to each block. The propagation speed of each block is estimated as the case in which the maximum reflection value of the reconstructed image is the largest after the F‐K migration process is carried out for several candidate values of the propagation speed. By means of this method, the distribution of the propagation speed can be estimated and a reconstructed image with high resolution can be obtained. This reconstructed image is of sufficiently good quality in comparison to the one by the phase‐shift method using the empirical propagation speed distribution. The processing time excluding the propagation speed estimation is reduced to one‐seventh that needed for the phase‐shift method.