Sonar mapping ventures into uncharted waters

Initiative aims to recruit range of vessels to locate seamounts.

Mountains, mountains everywhere: seamounts are less well mapped than the volcanoes of Mars. Credit: P. WESSEL/D. SANDWELL

Ships cruising the globe may soon be able to help scientists to chart seamounts rising from the ocean floor.

Less than 1% of the 47,000 known seamounts standing taller than 500 metres have been mapped in detail. In 2005, the dangers this poses became clear when the nuclear submarine USS San Francisco, travelling submerged about 600 kilometres south of Guam, struck an uncharted seamount, damaging the vessel and killing a sailor.

A new system using a basic GPS device coupled to a computer would allow anything from freight ships to pleasure yachts carrying sonar to help chart seamounts, which could number as high as 200,000, oceanographers say.

The initiative is an outgrowth of the Seamounts '09 Workshop, held 19–21 March at the Scripps Institution of Oceanography in La Jolla, California. The idea is to take advantage of single-beam and multi-beam sonar now aboard many vessels. "This is a really cool opportunity to take the baby step to image these features," says meeting chairman Hubert Staudigel of Scripps.

Theoretically, any vessel could gather data from regions of interest, but the quality of the imaging depends on how deep the ship's echo-sounder can probe. The ocean has an average depth worldwide of about 4,000 metres; a typical navigation sonar reads only to 1,000 metres, but that means it still could pick up some tall seamounts.

Government sonar data are typically hoarded for many years. The US Navy, for instance, is soon expected to release a massive cache of sonar survey data that it has gathered over the past few decades, says Christopher Fox, director of the National Geophysical Data Center in Boulder, Colorado; oceanographers hope that it will contain information on many unknown seamounts. Google has also been pushing for such data to be released to incorporate into its Google Ocean feature (see Nature 457, 1065; 2009).

In the meantime, oceanographer David Sandwell of Scripps and his colleagues have created a program to allow anyone to engage in seamount mapping. Soon to be made available online (http://topex.ucsd.edu/marine_topo), the program allows people to superimpose the routes of research ships over ocean bathymetry data that indicate where seamounts may exist. Ships steaming near these huge unprobed regions could then send in their data for analysis.

The trick now is to create an easy way to access and store the data centrally.

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Dalton, R. Sonar mapping ventures into uncharted waters. Nature 458, 557 (2009). https://doi.org/10.1038/458557a

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