Modeling the effects of a dynamic rough sea surface

Abstract

The strong sea surface reflectivity causes source- and receiver-ghost notches: areas in the wavenumber-frequency domain where the signal is very weak and consequently the SNR (signel-to-noise ratio) is low. If the sea surface is flat, these notches are very deep, but if it is rough and dynamic, they become blurred. The same strong sea-surface reflectivity also causes the surface-related multiples and its effect increases with each next multiple order. When modeling the ghost wavefield of an impulsive source in the case of a dynamic sea surface, an effective static sea surface suffices. The latter is composed of the surface areas that are ‘touched’ by the source wavefield at successive snapshots in time. However, such an effective static sea surface is not sufficient for the case of the detector ghost: here the dynamic character of the sea surface needs to be taken into account. We introduce a method for doing this by computing ghost operators for a number of snapshots in time and compose the final result from applying these. Our modeling method can be used to test algorithms such as deghosting. It can also be used to quantify the error that is introduced when the effects of the rough and dynamic sea surface are ignored, e.g., by replacing it by a flat sea surface in combination with an effective reflectivity that aims at incorporating the effects of a rough and dynamic sea surface.