Measurement and dynamic wavefield correction for time-dependent water velocity changes

Changes in water velocity produce significant 4D noise in time-lapse images. To be addressed accurately, the water-velocity problem requires two major ingredients: 1) water velocity must be estimated accurately at all acquisition times and for all shot/receiver locations, 2) time-variable corrections to the data must be dynamic to treat the full wavefield accurately. We present a new approach to parameterization of water-velocity changes which minimizes sensitivity to water depth. Dynamic correction of the wavefield is then achieved by designing 3D time-variable phase-shift operators. This is applied in a tau-px-py least-squares modeling process.