Despite the modern equipment, a tedious, confusing process
By David L. Chandler, Globe Staff, 07/21/99
It's not quite a needle in a haystack, but it's close: As ships troll the area off Martha's Vineyard in search of remains of John F. Kennedy Jr.'s plane, they have to contend with a sea floor jumbled with rocks, debris, and shipwrecks that may be similar in size and shape to the elusive wreckage.
A major problem facing the search effort, said research scientist Dana Yoerger of Woods Hole Oceanographic Institution, is that ''there's a lot of other stuff out there - rocks, shipwrecks and so on - and they don't really know what they're looking for. What would a smashed-up plane look like in side-scan sonar?''
On the other hand, he said, in this case the searchers do have the advantage that, because of the relatively shallow water, whenever a possible ''target'' is seen on the sea floor, they can quickly send divers into the water to check it out. In deeper water, they might have to wait to send a robotic submersible with video cameras to investigate potential targets.
Sending down divers to investigate every suspicious sonar target has been the procedure for the last two days, said a Coast Guard spokeswoman, Petty Officer Bridget Hieronymus. ''We had eight targets [Monday], and seven more this morning,'' she said yesterday, and in each of those cases, ''divers are sent down to systematically verify'' what those targets really are. The divers ''are moving from target to target until they find something.''
Conducting the search are two National Atmospheric and Oceanic Administration ships, the Rude and the Whiting, along with a Coast Guard cutter called Willow, which had sonar equipment installed on Monday for this search operation, and a Navy rescue and salvage ship, the USS Grasp, which in addition to side-scan sonar search capability is also equipped to recover wreckage.
The side-scan sonar equipment being used can provide images of a swath of sea floor extending out about 300 feet to either side of the ship's path, providing a detailed picture of any objects within that strip. The equipment aboard at least one of the ships, the Rude, was built by Edgetech, a Milford-based company founded by Harold ''Doc'' Edgerton, the late Massachusetts Institute of Technology professor and engineer who also perfected the technology for high-speed stroboscopic photography that can capture still images of speeding bullets.
Edgetech engineer Darren Moss, who demonstrates the side-scan sonar to clients and provides training in its use, said that just two weeks ago, he was demonstrating this equipment in Lake Michigan in a search for wreckage from another small private plane.
''The system is basically designed for this type of work,'' Moss said. Other kinds of side-scan sonar equipment are designed for other purposes, such as geological mapping, where the need is for wider coverage with less need for distinguishing small details. But this equipment, aboard the same NOAA ship Rude, for example, was also used successfully in the search for wreckage from TWA flight 800 off Long Island.
But the sea floor is large and littered, and the wreckage being sought may be in small pieces. ''This could take a long time, unless they get lucky,'' said Yoerger.
The process is difficult and tedious, and depends in part on high-precision navigation throughout the process.
Covering a search area methodically involves a meticulous coverage pattern - ''mowing the lawn, we call it,'' said Yoerger, who has been involved in many deep-sea searches. As in mowing a lawn, ''you don't want to cover some areas twice, but you also don't want to leave any gaps.''
The NOAA ships conducting the search are normally used for mapping potential obstructions, such as large protruding rocks or old shipwrecks, that can pose a hazard for ships in the area. The same equipment, which sends ''pings'' of sound down to the sea floor and then records the echoes with underwater microphones, is ideal for locating debris from a crash.
Although they don't know exactly what to look for, typically any man-made objects stand out because of their straight edges and sharp corners, unlike the rounded lines of natural objects such as rocks on the sea floor.
But even when a likely target shows up on the sonar, it takes time to investigate. Normally, a boat with divers is then sent to the spot, which it must identify through its own navigation systems. Then, ''the divers don't have any navigation once they jump off the side of the ship,'' said Yoerger, so it can be difficult to tell for sure if, for example, a rock they see on the bottom is really the same object as the target they were sent to investigate - especially when underwater visibility is poor.
But if the plane is intact, or in a few large pieces, ''it should make an excellent sonar target,'' said Clifford Goudey, a marine engineer at MIT. Even lobster traps can often be identified using such sonar systems, he said.
Goudey, who recently spent time at sea mapping the sea floor a little farther south of Martha's Vineyard, said ''you see rocks, sand ridges in the bottom, all sorts of things. But anything unusual is easy to identify.''
This story ran on page A13 of the Boston Globe on 07/21/99.
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