This chapter has introduced a new tomographic velocity analysis method that uses planewave synthesis imaging. In order to measure traveltime error in the image domain after prestack migration, residual moveout (RMO) velocity analysis is performed in common surface location (CSL) gathers after reflector-dependent planewave synthesis imaging. Since the reflector-dependent planewave synthesis imaging provides symmetric RMO with respect to the normal incidence angle to the reflector, the measured RMO velocity contains more accurate traveltime error information than that of surface-oriented planewave synthesis imaging. The measured traveltime errors are inverted to determine the errors in the reference slowness in terms of spline parameters, using the conjugate gradient algorithm. The test of the algorithm for a synthetic data set shows fast convergence to a true slowness model even in only one iteration. The algorithm is also applied to a field data set and the result is shown in chapter 6.