The conversion of the scalar recorded field into the elastic wavefield at the ocean floor and the subsequent separation of the converted wavefield can be achieved by the application of successive steps.
First the recorded pressure field is decomposed into the upcoming and downgoing wavefields (Claerbout, 1971), and since the downgoing wave at the cable is just the upcoming wave reflected at the water surface (or ghost), it is possible to express the upcoming wavefield as a function of the recorded wavefield. Then, the principle of survey sinking (Schultz and Sherwood, 1980; Claerbout, 1985) is used to extrapolate the upcoming pressure field down to the ocean floor. The next step is the conversion of the scalar pressure field into the displacement amplitude field of the P waves in the water; this conversion is accomplished through a simple relation in the w-kx domain. Finally, a slowness filter is used to obtain the displacement amplitudes of P and SV waves below the water bottom interface. This filtering process shows to be more effective if a prior separation of the data into P wave Snell rays domains is performed, so that a different filter can be used for each domain.