The impulse response of PSPM is computed by considering the PSPM process as the combination of full prestack migration followed by zero-offset modeling (Deregowski and Rocca, 1981; Deregowski, 1986). Popovici and Biondi (1989) proposed a general PSPM algorithm that transforms the prestack data to zero offset when the velocity is a general 2-D function. Raytracing is used for modeling wave propagation in a general 2-D medium. The algorithm constructs kinematically a DMO + NMO operator which has to be applied to the data as an integral (Kirchoff-style) method. The PSPM operator is identical in shape to the DMO operator, except that it contains a time shift which is the NMO. For a constant velocity medium, the PSPM operator is analytically expressed as a function of the source-receiver travel-time and dip angle.