SOUTH PORTLAND, Maine —
The expedition team ran two independently self-controlled robots known as autonomous underwater vehicles along the ocean bottom day and night. The torpedo-shaped AUVs surveyed the site with side-scan sonar, moving at a little more than 3 miles per hour as they traversed back and forth in a grid along the bottom, said Paul-Henry Nargeolet, the expedition's co-leader with RMS Titanic Inc. Dave Gallo from the Woods Hole Oceanographic Institution was the other co-leader.
The AUVs also took high-resolution photos — 130,000 of them in all — of a smaller 2-by-3-mile area where most of the debris was concentrated. The photos were stitched together on a computer to provide a detailed photo mosaic of the debris.
The result is a map that looks something like the moon's surface showing debris scattered across the ocean floor well beyond the large bow and stern sections that rest about half a mile apart.
The map provides a forensic tool with which scientists can examine the wreck site much the way an airplane wreck would be investigated on land, Nargeolet said.
For instance, the evidence that the stern rotated is based on the marks on the ocean floor to its west and the fact that virtually all the debris is found to the east.
"When you look at the sonar map, you can see exactly what happened," said Nargeolet, who has been on six Titanic expeditions, the first in 1987.
The first mapping of the Titanic wreck site began after it was discovered in 1985, using photos taken with cameras aboard a remotely controlled vehicle that didn't venture far from the bow and stern.
The mapping over the years has improved as explorers have built upon previous efforts in piecemeal fashion, said Charlie Pellegrino, a Titanic explorer who was not involved in the 2010 expedition. But this is the first time a map of the entire debris field has looked at every square inch in an orderly approach, he said.