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ABSTRACT: Side-Scan Sonar Mapping: Pseudo-Real-Time Processing and Mosaicking Techniques

W. W. Danforth, W. C. Schwab, T. F. O'Brien, H. Karl

The U.S. Geological Survey (USGS) surveyed 1,000 km2 of the continental shelf off San Francisco during a 17-day cruise, using a 120-kHz side-scan sonar system, and produced a digitally processed sonar mosaic of the survey area. The data were processed and mosaicked in real time using software developed at the Lamont-Doherty Geological Observatory and modified by the USGS, a substantial task due to the enormous amount of data produced by high-resolution side-scan systems.

Approximately 33 megabytes of data were acquired every 1.5 hr. The real-time sonar images were displayed on a PC-based workstation and stored on WORM (write-once, read-many) optical disks. Every 4 to 6 hr the data were transferred to a UNIX minicomputer where the sonar images were slant-range corrected, enhanced using an averaging method of desampling and a linear-contrast stretch, merged with navigation, geographically oriented at a user-selected scale, and finally output to a thermal printer. The hard-copy output was then used to construct a mosaic of the survey area.

The final product of this technique is a UTM-projected map-mosaic of sea-floor backscatter variations, which could be used, for example, to locate appropriate sites for sediment sampling to ground truth the sonar imagery while still at sea. More importantly, reconnaissance surveys of this type allow for the analysis and interpretation of the mosaic during a cruise, thus greatly reducing the preparation time needed for planning follow-up studies of a particular area.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990