EXTRACTION OF THE NORMAL COMPONENT OF THE PARTICLE-VELOCITY FROM MARINE PRESSURE DATA

We present a general wave theoretical method for extracting the normal component of the particle velocity from marine pressure data. A possible use of the normal component of the particle velocity and the pressure is the separation of upgoing and downgoing waves at the receivers. For one special acquisition geometry, the source wavelet can also be estimated. The method in principle is exact. No information about the properties of the elastic earth is required. When the pressure data are recorded on a single surface, it is necessary to know the source signatures if the source array location is above the receiver surface. If the sources are located below, the signatures need not be known. The locations of the individual receivers must be specified, and the reflecting properties of the sea surface must be known. When the receiver surface is plane and horizontal, the extraction process can be performed in the frequency-horizontal wavenumber domain. The normal component of the particle velocity can furthermore be extracted from pressure data recorded at two surfaces at different depths. In this case the reflectivity of the sea surface does not come into play; it is only the medium properties between the two receiver surfaces that enter the problem. The actual depths of the receivers need not be known, only their relative distances. If the sources are located above the uppermost receiver surface, the source signatures can also be estimated. A simple synthetic data example demonstrates the extraction of the normal component of the pressure from the pressure field recorded along a dipping receiver line below a free surface.