It is common in shallow seismic studies for the compressional-wave velocity in unconsolidated sediments to increase by a factor of four or more at the transition from dry or partial water saturation to full saturation. Under these conditions, conventional NMO velocity analysis fails and leads to large depth and layer thickness estimates if the Dix equation is assumed valid. Prestack depth migration (PSDM) is a means of improving image accuracy. A comparison of PSDM with conventional NMO processing for three field examples from differing hydrogeologic environments illustrates that PSDM can significantly improve image quality and accuracy.
Bradford, John H. and Sawyer, D. S.. (2002). "Depth Characterization of Shallow Aquifers with Seismic Reflection, Part II—Prestack Depth Migration and Field Examples". Geophysics, 67(1), . http://dx.doi.org/10.1190/1.1451372