VSP资料的单向隐式差分逆时偏移

REVERSE TIME MIGRATION OF VSP DATA BY UNILATERAL IMPLICIT DIFFERENCE

Based on the symmetrlzation of wave equation,by using the reverse time migration for VSP data processing,it is possible to image at the point where the upgoing and the downgoing waves intersected. In this way,the reflector could bemigrated to its original position. There are three steps which should be adopted in reverse time migration;(1)the extraction of the time for imaging;(2)the extrapolation of the recorded wavefield;(3)the image of reflector.The solution of wave equation is stfictly confined by limitations of steady conditions when explicit difference format is adopted,or it will be faced with a large quantity of work of time consuming if the implicit difference format is used. In this paper, the solving-of difference equation is by using the unilateral implicit difference format through pursuit technique. As a matter of fact,it not only answers the requirements of "ABSOLUTELY STEADY" ,but it also makes the extraction of solution easier and simpler,and the operation can thus become very time-saving. In this respect,it certainly opens a new way for solving the wave equation and provides an effective method for VSP migration.