Monday, May 08, 2006

 

Five-member team using photo-mosaics for sunken ships

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The Mercury News
By Susan Cocking
May 03, 2006


MIAMI - Thanks to a maritime heritage team with the Florida Keys National Marine Sanctuary, you might never look at sunken shipwrecks the same way again.

The five-member team has been working for more than a week to create never-before-seen pictures of five historic wrecks that make up the sanctuary's shipwreck trail - the City of Washington, Benwood, San Pedro, Adelaide Baker and North America.

You'll be able to view them in about two months at http://maritimeheritage.noaa.gov, and later they might be displayed at Keys dive shops and maritime museums.

Team leader Tane Casserley, a marine archaeologist with the NOAA office in Newport News, Va., and his colleagues are creating photo-mosaics of the sunken ships. Unlike ordinary underwater photographs, which depict a portion of a shipwreck from the shooter's point of view, a photo-mosaic provides an accurate picture of the entire shipwreck site - how it is laid out and what lies next to it on the ocean floor.

The process involved in creating an underwater photo-mosaic is innovative and fun. Casserley developed a video camera platform consisting of a sled propelled by two underwater scooters.

He glides over the wreck at speeds of up to three knots, shooting enough images with each pass to cover the entire site.

Twin SONAR devices mounted on the sled alleviate the camera-shake problem, ensuring that it remains at a consistent height over the wreck to produce accurate scaled images.

Later, on a computer, Casserley pieces the still images together to create the photo-mosaic.

Casserley and his team demonstrated their diver propulsion vehicle/camera platform for reporters Thursday on the wreck of the Adelaide Baker in 20 feet of water four miles south-southeast of Duck Key. (For those who would like to visit, the wreck is located at GPS coordinates 24 degrees, 42.175 north; 80 degrees, 53.670 west.)

Built in 1863 in Bangor, Maine, it is a 153-foot-long sailing ship whose remains are scattered for about 1,400 feet along the bottom in two main clusters.

The most prominent feature is the 77-foot iron main mast surrounded by scattered rigging. Originally named the F.W. Carver, it was sold to the British and renamed the Adelaide Baker. In January 1889, bound for Savannah, it wrecked on Coffins Patch Reef with a load of timber.

On Thursday, Casserley gave reporters and videographers wearing scuba gear demo rides on the sled as it glided over the wreck.

Lurking beneath a coral-coated section of rigging was a large green moray eel that flexed its jaws, but made no aggressive moves toward the human visitors. Other remains of the ship were loaded with reef fish and colorful tropicals, and a bulbous porcupinefish inhabited the hollow end of the main mast.

Besides yielding archaeological information and a dive map, the photo-mosaic of the Baker and other shipwrecks will provide a baseline measurement to gauge the effects of hurricanes.

Said Casserley: ``The photo-mosaic is a snapshot in time. You can come back next year and see what damage was done to the wreck sites.''


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