Wednesday, December 28, 2005

Sonar and Bubble Updates for the New Year

Mud-trapped, methane gas occasionally bubbles to the surface from the ocean floor, according to a team of University of Maine scientists reported in Maine Ocean Floor Has Mud-Trapped Gas. Some 70 known gas fields have been identified off Maine's coast. Massive gas bubbles crater or pit the ocean floor when they rise, according to the scientists, who are publishing their findings in Marine Geology magazine. Because the gas in trapped in mud, it would cost too much to extract it for commercial energy purposes.

The largest crater is the size of a football stadium. Most of the craters are between 32 feet and 260 feet in diameter. The largest, in Belfast Bay, is more than 650 feet wide and 100 feet deep.

Through the years fishermen have reported seeing bubbles and plumes of mud. Charles Paull, lead scientist at the Monterey Bay Aquarium Research Institute in California, however, said he has yet to see evidence that the craters are produced by gas.

Possible reason for methane bubbles: Decaying whale carcasses? Submarine garbage ejectors? ...We weighted the bags so that they went directly to the bottom and did not give away our position.

Suppose whales swim over a crater as a large gas bubble erupts? Would we get a disorientated mammals? Probably unrelated to whale beaching deaths as waters are much too shallow.

Brutal Bubbles: Collapsing orbs rip apart atoms Fill a flask with liquid, rattle it with ultrasonic waves, and hellish conditions can form in the resulting fluid. Tiny gas bubbles swell before imploding with a fury extreme enough to strip electrons from atoms trapped in the collapse. Illinois chemists who have detected such atomic destruction have also directly measured temperatures of the imploding bubbles this year. Some temperatures have been on the order of at least 15,000 kelvins (about three times as hot as the Sun's surface).

Researchers have known for years that ultrasonically generated bubbles emit light flashes when they collapse —a phenomenon named sonoluminescence. While some scientists claim that thermonuclear fusion may occur in such implosions, others had suggested a plasma—a vapor of electrons and ions—forms in imploding bubbles. No one, however, had evidence of such a condition until David J. Flannigan and Kenneth S. Suslick of the University of Illinois at Urbana-Champaign reported light emissions suggestive of a plasma.

Bubbles and Ambient Noise Sonar (ANS)
Detection in the littorals: the increased levels due to boat traffic increase 25 dB, up to 97 dB re 1mPa at 1.5kHz. (note: MUX refers to multiplexer)

and, here: The data set should help us to assess the ways in which bubble clouds are formed and move about in the near surf zone. ...The results should provide a useful basis for comparison with models that include the surf zone dynamics.

(There is much more a clever searcher will find)

Snapping Shrimp Drown Out Sonar With Cavitation The oceans' shallow waters are noisy places with the waves, rain, and biologicals. Loudest of all are colonies of snapping shrimp, the bane of military and scientific efforts to "see" through the ocean using sonar: here
Scientists had assumed that the snapping noise occurred when the two parts of the claw banged shut. Now, however, a team of physicists and a biologist have discovered that the noise, in fact, comes from the collapsing of small bubbles generated by the claw's closing motion. The bubbles form through a process called cavitation.


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