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3-D Images Give New Life to Old Shipwrecks

It's no nightingale, but a new seismic technology nicknamed Chirp is making music for the ears of archaeologists interested in the wrecks of sunken ships.

Named for the bird-like blips it makes in action, GeoChirp 3-D is able to generate three-dimensional images of just about anything lying beneath the sea floor, including shipwrecks hidden under years of muck and sand build-up.

Chirp is "a seismic system that works by firing sound waves at the seafloor and measuring the reflections as they bounce back from objects and different rock layers in the seabed," writes the U.K.'s Engineering and Physical Sciences Research Council (EPSRC) in a recent edition of its quarterly publication Newsline.

Unlike the traditional two-dimensional method of slicing the seabed vertically from the top down, Chirp produces a cube of information.

"The processed output from this system is a true 3-D 'volume,' as though when looking at the seabed you had switched on your 'X-ray vision' and were able to see buried objects," explained Peter Hogarth, technical director with GeoAcoustics Ltd., the manufacturer of Chirp.

The oil industry has used a similar 3-D seismic system for several decades to detect untapped pockets of hydrocarbon. In that industry, a less detailed resolution over a wider area works just fine, said Justin Dix, professor of marine geophysics and geoarchaeology at Southampton University.

For studying shipwrecks, the resolution needed to be much more focused.

"Archaeology is precise," Dix said in a recent telephone interview. "Unlike the oil surveyors, we wanted to know what was happening between the lines down to a few centimeters' accuracy."

Currently, Dix and other researchers from the university's School of Ocean and Earth Sciences (SOES) are using the equipment to explore The Invincible, a mid-18th century English naval vessel. The wreck, which sits partially buried off the south coast of England, has been the focus of study since 1980.

Shipwrecks are ideal candidates for systems like Chirp because wooden material sends off very strong seismic reflections, Dix said. Chirp's non-invasive nature also makes it a perfect fit for the field of maritime archaeology in general.

"The primary role of this new technology is to protect heritage," he said. "We can't bring ships up to display in museums, so the focus with a wreck becomes what we can find out without actually touching it."

With the Invincible, 3-D models will be given to dive teams so they know exactly where to look, thus minimizing damage their presence might do to the ship.

The technology wouldn't be good for discovering new wrecks, according to Dix.

"Chirp can cover a small footprint of couple of hundred meters squared, which is great if you have an idea of where to look," he said. "It can't survey large areas."

Dix expects the new system will take him to Norway next, where he plans to explore Viking ships nearly a thousand years old.

The 3-D Chirp sub-bottom profiler was developed by the National Oceanography Centre, Southampton (NOCS) in collaboration with GeoAcoustics Ltd. and the Institute of Sound of Vibration Research (ISVR) at Southampton University.

The project was funded by the EPSRC, GeoAcoustics Ltd and English Heritage.

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