Acoustics 2008: Burglar Alarm for Ancient Shipwrecks

For all those interested in great naval disasters, lost underwater cities, shipwrecks, or The Life Aquatic with Steve Zissou, you might be interested in SEA-GUARD, an underwater intruder alarm system developed by Turkish scientists and presented at this year's Acoustical Society of America (ASA) meeting in Paris.

According to the authors of the paper, it is estimated that there are still about 1 million undiscovered ancient shipwrecks settled over the vast ocean floor. As more and more discoveries are made in the future, the potential for theft of valuable artifacts and damage to found vessels and cargo presents a challenge to those seeking to preserve these deep sea relics.

SEA-GUARD aims to protect these archaeological sites from unwanted or unauthorized visitors. It works by monitoring the underwater acoustic field, or sound waves surrounding the archaeological site.

Comprised of two sensor packages (one on the sea floor at the site, the other at a surface buoy), the device can detect unusual activity from disruptions in nearby sound waves. Not only that, artificial intelligence allows SEA-GUARD to analyze the specific behavior of an intruder, hence it is unlikely to confuse 5 grown men with a school of fish. Finally, once a genuine threat is confirmed, the system can send an alarm to authorities on land, via cable. Time to start searching for that buried treasure!


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MEDUSA's Sound Inside Your Brain

The sounds of MEDUSA do not come from the vehement, shrill cries of a woman whose head is covered in snakes, but are created by Mob Excess Deterrent Using Silent Audio (MEDUSA), a device that uses microwaves to beam sounds into your brain. And only you can hear them.


The U.S. military has been dabbling with the idea of a "microwave ray gun" for the past decade, but there has never been any attempt at laboratory development until recently.

The gun works by shooting short pulses of microwaves into your head, which quickly heat up brain tissue (much like how they heat up your leftovers). This causes a shock wave, which reverberates throughout the skull and is picked up by the ears. The sound produced is completely "inside your head", no one can hear it except for you, unless the pulses are aimed at multiple targets.

MEDUSA is touted as a non-lethal method of control by inescapable discomfort and irritation. For example, the device could be used to beam sounds at a rowdy crowd of people (er, or peaceful protesters, take your pick). Although research with more powerful microwaves is needed, scientists working on the device say MEDUSA might have serious harmful effects. The force from the shock wave could cause brain damage, or even death, making it an effective (and far less messy) military weapon.

Far-fetched commerical uses for MEDUSA have also been proposed, such as beaming subliminal advertising messages into people's brains, say, while shopping. Creepy.
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The Earth is Screaming

Astronomers have recently confirmed that the earth sounds like a three year old throwing a tantrum.

Recordings from space have captured the unpleasant noise, which may be heard by extraterrestrials.

We already know the planet emits a quiet hum, most likely caused by our continuously moving oceans, or our turbulent atmosphere. The radio waves that cause the screeching sounds are created by particles that collide as the solar wind passes through the earth's magnetic field.

New data from the European Space Agency's Cluster mission show that the radio waves, called Auroral Kilometric Radiation, burst into space from the earth in narrow, flat beams.

New technology has enabled researchers to pinpoint exactly where the noise is coming from. Scientists located 12,000 spots around the earth that send out the radio waves, each is about the size of a large city.

So why don't we hear them? A charged atmospheric layer called the ionosphere blocks the radio waves, preventing them from reaching the earth. But that doesn't mean the waves aren't strong.-they are 10,000 times greater that the strongest military signal, that's enough to drown out every radio station on the planet.
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Acoustics 2008: Noisy Red Cars

The acoustics folks are meeting in Paris this week for the Acoustical Society of America's (ASA) 15th annual meeting, and I'll be covering all the coolest (er, what I deem as cool) research here on the blog. Simply put, acoustics is the study of sound. But the field is widely diverse and aside from music, applied to countless other areas like oceanography, architecture, and medicine.

In one of the many interesting papers being presented at the conference, German scientists designed an experiment to test whether different colored images influence how loud a sound is perceived to be. Visual and audio stimulation often go hand in hand, for example, as you glance at car driving down the street you also likely hear the noise its motor makes.

The authors had participants look at pictures of red, light green, blue, and dark green sports cars while listening to the sounds of an accelerating sports car. Based on participants ratings, the study found that the sound coupled to the red car was perceived to be about 5% louder than the same sound coupled to a light-green car. Interestingly enough, dark green cars seemed louder to participants than light green or blue.
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Whales versus Waves

Sound waves, that is. The Supreme Court recently decided to hear the U.S. Navy's appeal of a federal court ruling that banned sonar within 12 miles of the coast, and ordered the immediate termination of high-powered sonar when whales (and other marine animals) have been detected. In light of the sonar-whale dilemma, it might be helpful to run through the basics of underwater acoustics.

Sonar is the process of detecting what already happens to sound waves whenever there is a noise: an echo. As sound bounces off surrounding objects, some of them are reflected back to the noisemaker. The acoustic sound waves in sonar (an acronym for SOund Navigation And Ranging) are transmitted through the water in short pulses, where they travel at frequencies high above what humans can hear.

The reflected wave signals can then be detected and used to infer the distance and relative position of an object. The military uses sonar to detect enemy submarines and other tools of aquatic warfare. Keep in mind that the speed of sound in water can change, depending on the depth, temperature, and even how salty the water is. So sound waves in an ocean will travel at a different frequency than sound waves in a large pool or lake.

The interests on each side of the debate couldn't be any more conflicting. The Bush administrations argues (in the name of national security) that the Navy should be given permission to disregard current environmental laws that protect endangered species, and work themselves into a sonar power frenzy if needed. Plus, they say they already take precautions to protect whales. But the environmentalists say sonar has been proven to harm whales and other endangered marine mammals to the point of death.

While the mechanistic details of how sonar affects whales are unknown, scientists are certain a link between the two exists. Several studies published in Nature over the past couple of year have provided evidence of the adverse effects of
sonar.

It is thought that sonar causes abnormal behavior in whales, causing them to disorient themselves and surface the water too quickly, leading to a condition called decompression sickness. In addition, autopsies performed on whales that died on the Canary Islands hours after a mid-frequency sonar was sent out (as part of an international military exercise), show that there may also be physical effects to sonar. CAT scans showed bleeding around the brain and ears of whales, along with an excess of gas bubbles that filled bodily tissue.
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Squeezing Song from Sand

You can't squeeze blood from a stone, but you can get sound out of sand dunes. Singing dunes often make sound on their own, as a result of spontaneously coordinated avalanches of sand, according to a paper recently featured in Physics News Update.

What I hadn't realized is that people can effectively play the dunes by pushing sand to create their own avalanches. The researchers who studied the sounds of the dunes collected some videos of people scooting down dunes to make tones, and posted the clips on their (poorly designed) web page. They also built the apparatus shown above to make their own sand sounds.
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