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MH370: How do underwater sonar subs work? - Valley News Live - KVLY/KXJB - Fargo/Grand Forks

MH370: How do underwater sonar subs work?

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Four pings and an oil slick. That's what the search for Malaysia Airlines Flight 370 has yielded so far.

No signs of wreckage, no assurances of exactly where the plane might be.

So officials are launching their next option: an underwater vehicle to scan the ocean floor.

But even that vehicle -- the Bluefin-21 -- faces plenty of challenges in finding the plane carrying 239 people.

The Bluefin-21 is a probe equipped with side-scan sonar, or acoustic technology that creates pictures from the reflections of sound instead of light.

The device sends a pulse that produces a three-dimensional map of the seafloor, according to the U.S. Navy, which owns the Bluefin-21 used in the search. An operator on the surface programs the vehicle.

"When it reaches the appropriate depth, it will turn on its sensors," said David Kelly, the president and CEO of manufacturer Bluefin Robotics.

"It will then run what's called the lawn mower pattern, which is a series of parallel lines or tracks, where it will go back and forth just like mowing your lawn."

The Bluefin-21 will be launched in the most probable area of the pings that were detected by the Australian ship Ocean Shield.

From there, it will plunge to a depth of 4,000 to 4,500 meters (2.5 miles) -- roughly 35 meters above the ocean floor, the U.S. Navy said.

"It operates at a height above the bottom optimized for its sensors," Kelly said.

The Bluefin-21's first mission will cover about 40 square kilometers (3.1 miles by 4.9 miles). It'll probably take anywhere from six weeks to two months to scan the entire search area, the U.S. Navy said.

That's because the vehicle crawls at the pace of a leisurely stroll, said Sylvia Earle, an oceanographer from National Geographic who was chief scientist for the National Oceanic and Atmospheric Administration.

But the Bluefin-21 does create good images -- so good that they are "almost a picture of what's there ... but it's imaged with sound instead of with a camera."

The bottom of the search area is not sharply mountainous -- it's more flat and almost rolling, Australian chief search coordinator Angus Houston said.

But he said the bottom of the area probably has a lot of silt, which can "complicate" the search.

Houston cautioned against beliefs that the underwater vehicle will find wreckage.

"It may not," he said. "This will be a slow and painstaking process."

The vehicle has a 24-hour cycle, so it can be deployed only once a day. And no information will be available until the end of each cycle, Houston said.

It will take two hours for the Bluefin-21 to get down to the search area. Then it will scour the ocean bed for 16 hours and take another two hours to resurface. After that, it will take another four hours to download and analyze the data collected, Houston said.

"The rate of information flow is certainly going to be a little bit more than a day apart," Matthews said.

Once the debris field is found, other equipment -- such as remotely operated vehicles -- would be brought in to recover the black boxes, Earle said.

ROVs working at depths of 3 miles would require power conveyed down a cable from a ship above, said. "There are not many pieces of equipment in the world able to do this."

And only a handful of countries have manned submarines capable of descending to such depths -- such as the United States, Russia, Japan, France and China, she said.

It's actually not that surprising, said CNN aviation analyst David Soucie, author of "Why Planes Crash."

The model used for tracking the debris could be incorrect, Soucie said. He said that was the case when investigators were searching for evidence of Air France Flight 447, which plunged into the southern Atlantic Ocean in 2009, killing all 228 people aboard.

"They spent weeks looking for debris in the wrong area," he said.

The lack of debris could also mean that the plane did not break apart on impact, but instead sank largely intact, he said.

If that was the case, it could complicate the effort to retrieve the black boxes, since they were stored inside the tail of the plane. Investigators would have to dismantle the tail in order to extract them and whatever secrets they may hold.

 

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