Performance evaluation of a high-resolution sub-bottom profiling system

Abstract

The design and performance of a modern digital high-resolution sub-bottom profiling system are reviewed. The system is designed to identify drilling hazards in about the first 3000 ft of sea floor. Performance comparisons with a conventional active sonar are made using metrics such as figure of merit. The sound source is a sparker; the receiver a towed line array. There are two stages of signal processing: the first stage is applied to each hydrophone channel, and the second stage in the combination of all channels. The first stage includes pulse compression (zero phase least-squares Wiener filtering using a source monitoring hydrophone system), the removal of surface-images (“deghosting”), and the reduction of bottom-surface multiple reflections (“dereverberation”). Two near-field moving-focus beam steering second stages are compared; CDP (common depth point) stacking and Tucker et al.'s within-pulse electronic sector scanning. Typical sub-bottom records will be shown and the effectiveness of various processing steps illustrated. Also discussed are techniques for quantifying reflection coefficients to aid in lithologic interpretation and of “seismic modeling” to help unravel records with overlapping returns.