Joint Time-Frequency Analysis (JTFA) can estimate the speed of moving targets in Synthetic Aperture Radar (SAR) images. These targets are usually solid targets. JTFA estimation of water surface speeds is more difficult since the returns are generated by Bragg scattering epochs that are randomly distributed in the radar's footprint - in both time and space. The spectral characterization of these returns depends strongly on the geometry of the collection, which also affects the techniques needed to estimate the speeds. A novel phase differencing technique is presented to measure the frequency offset caused by the range motion of the surface water. JTFA is applied after extensive filtering to extract the motion induced component of the phase signal.