Archive for 08/02/2012

Lynn Brennan –

When most people think of scuba diving, they imagine crystal-blue waters, colorful fish and tropical paradises.

Conditions the Missouri State Highway Patrol dive team faces stand in stark contrast to that vision.

“About 90 percent of the dives that we dive in is in black water — where you can’t even see your hand in front of your face,” said Trooper Jason Kuessner, one of the dive team’s nine divers.

“You can take a flashlight around with you and shine it in your face and you can’t see the bulb burning.

That’s why training in this clear water, it helps guys get comfortable with their equipment and their gear.”

Kuessner and the eight other members of the dive team spent a hot summer day in the cool waters of the Quail Run Diver’s Quarry in Rolla conducting panic avoidance training.

“Today we’re doing emergency out-of-air exercises,” said Sgt. Kurt Merseal, dive team leader.

“We’re doing what we call zero-visibility ascents and descents.

Most of our diving is zero-visibility. You can’t see anything. So what we’ll do is, we’ll drop down to about 30 feet and we’ll black out a mask.

We’ll have you do what is called a controlled ascent.

Sometimes people have trouble with vertigo when you can’t see – you don’t know if you’re going up or down or sideways.

It’s a good way to overcome that.

Then we’ll actually do it without a mask so you’ll lose your primary mask, you’ll have something to breathe from, but your nose is exposed, your eyes are exposed, you have to work your way up slow.

Here it’s easy, but when you’re in 100 feet of black water, it’s tough.”

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Sweeping below deck

Posted: 08/02/2012 in all marine news

The Economist –

For years navies have employed human divers, dolphins and sea lions to search for explosives attached to the hulls of warships by a scuba-diving enemy.

While these mine-finding tactics work, they are less than ideal.

Divers can be killed or injured and marine mammals are extremely costly to maintain on a boat.

The mines are also getting smaller and harder to detect.

The idea of using aquatic robots to search for the mines instead is alluring, but it is difficult to teach machines how to navigate around hulls without crashing into them or getting lost.

Franz Hover and Brendan Englot at the Massachusetts Institute of Technology (MIT) have come up with a way to improve things by using a two-step process.

Programming robots to scan hulls would have been relatively easy if limpet mines were still as large as watermelons.

The robot would simply be told to maintain a safe working distance and swim back and forth using its sonar cameras to generate an image of the hull’s topography.

If the generated image perfectly matched that of a clean hull stored in the robot’s memory, the robot would know that there were no mines attached.

If not it could raise an alarm. Yet nowadays mines can be as tiny as a small iPod, which might not blast a hole in the hull but if carefully placed could disable a ship’s propellers.

The problem, then, is one of definition.

Sonar scans done at a safe distance of 10 metres create a rough image known as a data-point cloud. But this lacks the detail to spot small explosive charges.

The addition of vision cameras may not do much to assist since harbour waters are often murky.

To work around these problems, Dr Hover theorised that the data-point cloud could be used not to spot mines but as a guide to help the robot take a closer look at the hull.

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