Gwangsu HO (I),Akira KAWANAKA (I), Noboru NAKAYAMA (II),
Mikio TAKAGI (III)

(I) Faculty of Science and Technology,Sophia University
Mailing address :Department of Electrical and Electronic Engineering
Faculty of Science and Technology Sophia University
7-1,Kioicho,Chiyoda-ku,Tokyo 102 Japan
Telephone :03-3238-3421 Telefax 03-3238-3321

(II) Research and Development Center,OSAKA GAS CO.,LTD.
Mailing address :Research and Development Center,OSAKA GAS CO.,LTD.
6-19-9,Torisima,Konohana-ku,Osaka 554,Japan
Telephone :06-462-3231 Telefax :06-464-1805

(III) Institute of Industrial Science, University of Tokyo
Mailing address :Institute of Industrial Science, University of Tokyo
7-22-1,Roppongi,Minato-ku,Tokyo 106,Japan
Telephone :03-3402-6321 ex 2646 Telefax :03-3402-6226

Abstract

It has been developed the techniques which have been imaging optically opaque region using an electromagnetic wave radar in order to estimate the location of objects in the region. One important application of these techniques is the detection of buried pipes and cables. In case of subsurface radar, its image quality often becomes low because the nature of soil is not uniform and an electromagnetic wave is attenuated in soil. Hence, the method which improves the quality of the radar images is required. The migration has been using in seismic data processing. In F-K migration method and Phase-Shift migration method ,the solution of wave equation are obtained in Frequency domain. The propagation velocity of electromagnetic wave which varies in soil is an important factor for radar image processing. In Phase-Shift migration method, it can be assumed that the propagation velocity of electromagnetic wave is variable with the layer. But it is a problem that this method requires a long computation time. In F-K migration method, it is possible to calculate in fast time by using FFT algorithm. But in this method,the propagation velocity of electromagnetic wave is assumed to be constant. In this paper, we propose a method applying the F-K migration method into the divided image blocks in order to take account of nonuniformity of the propagation velocity. In this method LOT(Lapped Orthogonal Transform) was applied. LOT is a new block transform method which basis functions overlap in adjacent blocks, and it has a fast computation algorithm. It makes possible to process all blocks taking account of continuity and avoid the problem that the image of bried object was interrupted. The result of applying the proposed method to the subsurface radar images is presented. It points out the good capability for the image quality improvement taking account of the propagation velocity of each block ,and we report that this method has fast calculation capability.