Project SWATHMAP: Military sonars in service to science

Abstract

Project SWATHMAP (one of four deep‐water, long‐range sidescan sonars in operation today) is the low‐cost geologic application of a U. S. Navy antisubmarine warfare system utilized on routine ocean‐wide deployments. While resolution is not sufficient to observe bathymetric structures in detail, the system is particularly adept at locating them, discerning scale and shape, and determining continuity. Routine observations include terraces, trench crossings, seamounts (many of them newly discovered) often topped by craters, fracture zones, and abyssal hills (both superb clues to plate tectonic motion). Discoveries on this scale are essential for ground truthing the next decade's satellite altimeters. Certainly there are sidescan systems that do a better job of seafloor mapping than American combat vessels, but their cost is extraordinary by comparison and well beyond the reach of most nations. By contrast, even the humblest antisubmarine warfare‐equipped navy can use such a system to locate most substantial features within its exclusive economic zone. Possible system upgrades include (1) two‐sided scanning for maximum coverage, (2) stereo image production from parallel passes or sequential imaging, (3) digital tape recording for subsequent image manipulation and enhancement, and (4) decipherment of parallax across the array to determine the acoustic arrival angles one utilizes to estimate bathymetry.