Abstract

Two-component ocean bottom cable (2C OBC) data are often affected by substantial noise. The noise is probably caused by shear wave energy registered on the vertical geophone. It exhibits random properties in common shot domain but coherent properties in common receiver domain. This phenomenon is observed in most OBC surveys worldwide, and the noise level can be very substantial. Typically, there is a substantial moveout difference between the noise and the signal, i.e., reflected PP waves, allowing use of velocity filtering for noise suppression. Velocity of sound in water can be used as a quite universal parameter for normal moveout (NMO) correction before the velocity filtering. The NMO correction substantially simplifies design of the velocity filter. Efficiency of the proposed approach is illustrated using real 2C OBC data.

Introduction

The hydrophone and vertical geophone (2C) OBC data can be combined to provide a powerful method for eliminating multiples. A combination procedure may rely upon the proper relationship between the hydrophone and geophone data sets. The proper relationship can be masked when noise is present on either or both of the two components, and the effectiveness of the 2C OBC combination, i.e., the multiple suppression, may be greatly reduced. Therefore, noises should be removed from OBC data before the 2C combination. The purpose of this paper is to present a simple and effective procedure for removing noise that commonly corrupts OBC data.

Most suggested theories define the observed noise as related to shear wave energy recorded on the vertical geophone. For example, Claerbout (1990) pointed out that due to nonvertical incidence of P- and S-reflected waves at the water bottom, there is so-called 'crosstalk' between vertical and horizontal geophones. Li and Yuan (1999) attributed the noise to nonperfect coupling and orientation of OBC geophones. Reid and Macbeth (2000) have treated the problem in terms of vector fidelity.

This content is only available via PDF.
You can access this article if you purchase or spend a download.