19 June 2001



B. Bourgeois
Naval Research Laboratory
Stennis Space Center, MS 39529-5004
A. Martinez
Tulane University
New Orleans, LA



Bathymetric Surveying: For many decades bathymetric surveys have been conducted using vertical single-beam sonar systems. Surveys were conducted using a series of preplanned navigation lines based on historical knowledge of an area's depth, and acoustic imaging systems were used to ensure that shallower areas did not exist between the sounding lines. Modern swath bathymetry systems provide multiple soundings with each sonar ping, within a swath perpendicular to the ship's track. As compared with single-beam Systems, swath systems can provide 100% bottom coverage, yielding denser soundings and faster coverage of an area. Swath systems are typically operated at or near the ocean surface in order to maximize bottom coverage with time. Since a swath sonar covers an angular sector (as large as 1500 for some systems) the actual swath width on the ocean floor varies with ocean depth - narrower in shallow water and wider in deep water. Also, the effective swath width of these systems is adversely affected by environmental conditions such as sea-state, sound velocity profile, bottom morphology and bottom composition. The consequence of these factors is that it is difficult to predict a priori the effective swath width and to preplan navigation lines for minimum survey time while ensuring complete bottom coverage. Consider a simple case, where a series of parallel lines are to be run over an area with a slope, and the lines are oriented perpendicular to the contour of the slope. If planned line spacing is computed using the average depth and the nominal swath width, the result will be excessive overlap between swaths in the deep areas (wasted survey time) and gaps between swaths in the shallow areas (missing data).

Sponsored by the Oceanographer of the Navy via SPAWAR PMW 185.

Published in the 1999 Naval Research Laboratory Review, April 1999.
Naval Research Laboratory Contribution Number NRL/PU/5230 99-373.
NRL Journal Article