The traveltime curves or maps required for migrating converted waves (C-waves) depends on Pand S-wave velocities of the medium where the wave propagates. Consequently incorrect vp/vs-ratio (equivalent Poisson's ratio) leads to incorrect depth images. An indication of errors in the interval Poisson's ratio model is residual moveout and depth deviation in the prestack depth migrated PS-image gathers. These depth deviations are used in estimating interval Poisson's ratio in an iterative optimization method following the principles of reflection tomography. The technique is based on a linear operator that describes depth shift in C-wave image gathers (compared to PP-wave image gathers) function of changes in Poisson's ratio model. We assume that the reflector depth is known from previous P-wave velocity analysis. Raypaths are traced through a selected initial Poisson's ratio model and are combined with depth deviations in the process. The perturbations are added to the initial Poisson's ratio function to obtain the updated Poisson's ratio. Having the correct Poisson's ratio the shear velocity model and the contrast are directly obtained. The interval Poisson's ratio determined using this method is more accurate than from conventional methods. A fast and robust finite difference traveltime computational tool is used for the migration. The method is evaluated by test on a 2D synthetic and field dataset acquired in southern Germany.