Common reflection point (CRP) gathers are usually parameterized in terms of offset. For tomography, a more convenient parameterization is in terms of reflection angle. Reflection angle CRP gathers can be constructed using wave equation migration. By performing tomography in vertical travel-time (tau), focusing velocity, rather than some combination of focusing and mapping velocity, can be estimated. By using anisotropic preconditioning oriented along bedding planes, the solution can be guided towards a geologically reasonable model. The benefits of the tomography method are shown on a 2-D line from a 3-D marine dataset.