New Weapon Designed to Zap Scuba Divers

[Dragon2115]

I read the patent application and this is a really cool system. It's a targeted sonar. But in order to understand how it works and why it is so cool you need to understand a little about wave propogation and how sound cancellation technology works, mainly because this is the direct opposite.

Sound cancellation works because a secondary sound emitter produces an identical copy of the sound that is trying to be reduced, only 180 degrees out of phase. When the two sounds meet they cancel each other out. There is a catch however, if the two sound sources are placed apart from each other the cancellation effect only occurs at a specific location. Move a few feet in any direction and the phase relation of the signals changes and you lose the cancellation effect.

In fact, at certain places the signals will combine and amplify each other. That is the basis for this system. By playing with the phase shift they can choose exactly where that will be. Just hope you're not at that location.

What makes this such a great system is that as we know, normal active sonar is dangerous to everything that is too close to it including marine mammals. This system will allow the targeting of a specific threat while at the same time having no more than an annoying effect on nearby dolphins, whales, etc. It will also allow for the intensity of the disturbance to be controlled so there will be the choice of annoying the diver until they leave (for cases of lost divers that inadvertantly wander into a resitricted area) or killing them if they persist in trying to approach the ship being guarded such as in the case of a true attack.

I think this is a great system and should go a long way toward protecting vital assets without needlessly harming nearby marine mammals.

 

[Lonefox]

Here's an interesting article on other marine anti terrorism activities. Didn't realise that rebreather owners were effectively being checked out.

"Agents are now seeking the names of anyone in America trained in the use of rebreathers. "If, say, traffickers came to retrieve drugs attached to a ship's hull, we would watch for exhaust bubbles if they were using scuba tanks. But they could come unnoticed- terrorists usually have unlimited expense accounts, and they could afford the best rebreather units!" says Sierra."

http://www.divernet.com/profs/0105terrorsquad.shtml

 

[mikswi]

I was poking around a military website and came across this. I was reminded of the thread on this site and thought I would post it if anyones intrested in other applications to this technology.

http://www.defensetech.org/archives/002133.html

 

[mstevens]

Would you feel the same way if your wife or children were on a vessel that was launched by a terrorist attack?

I've never heard of a vessel being launched by a terrorist attack. However, if a terrorist attack were launched against a vessel they were on, yes I would feel the same way. This is true even if the attack were via scuba, which seems very unlikely compared with the numerous less risky options available to terrorists. Your argument here is highly pertinent to one of your later questions, so hold that thought.

We live in a dangerous time, and must do what we must do.

Humans have ALWAYS lived in dangerous times. The old "end justifies the means" argument is, and always has been, entirely un-American and flies in the face of everything I believe and hold sacred.

We have no business diving near any vessel that would have need for such a device.

Well, if my wife and kids are on it, it's a civilian vessel. What conceivable basis could there be for indiscriminately killing divers who get too close to, say, a cruise ship? How about a millionaire's megayacht? What if that megayacht cruises over my dive site with their system on? Who decides what sort of vessel has a need for these devices? Generally, it's those with either political or financial clout, and there are plenty of the latter around the globe. I would not for a moment presume that only US military vessels will have access to this technology, given enough time.

 

[Don Burke]

Sound cancellation works because a secondary sound emitter produces an identical copy of the sound that is trying to be reduced, only 180 degrees out of phase. When the two sounds meet they cancel each other out. There is a catch however, if the two sound sources are placed apart from each other the cancellation effect only occurs at a specific location. Move a few feet in any direction and the phase relation of the signals changes and you lose the cancellation effect.

In fact, at certain places the signals will combine and amplify each other. That is the basis for this system. By playing with the phase shift they can choose exactly where that will be. Just hope you're not at that location.

What makes this such a great system is that as we know, normal active sonar is dangerous to everything that is too close to it including marine mammals. This system will allow the targeting of a specific threat while at the same time having no more than an annoying effect on nearby dolphins, whales, etc. It will also allow for the intensity of the disturbance to be controlled so there will be the choice of annoying the diver until they leave (for cases of lost divers that inadvertantly wander into a resitricted area) or killing them if they persist in trying to approach the ship being guarded such as in the case of a true attack.

I think this is a great system and should go a long way toward protecting vital assets without needlessly harming nearby marine mammals.

The problem is that a body of water is not a very predictable medium for such propagation. One thermocline and all of the computations are out the window.

If the diver is that close, a concussion grenade would be appropriate. If the diver is too far away for a concussion grenade, why does he need to be killed?

There are easier and cheaper ways to fend off a diver.

It is a lousy excuse for a security system.

 

[Lonefox]

Sounds can be cancelled out in a laboratory environment by way of phase shifting the sonic waves by 180 degrees, which is the principal that this system works on, however the real world conditions are a lot different. Submerged items, harbour walls etc could reflect the phase shifted waves, and in some cases they may combine with the original wave "in phase" and create a new waveform with 2, 3 or even more times the potential of the original wave, in essence creating an unintended more potent kill zone.

It's a case of simple mathematics, if you merge two waves out of phase they cancel out, if you merge two waves in phase they double up. A real world example is terrestrial television signals bouncing off of buildings, ghosting is a result of phase shifted radio waves.

In essence, such a system is unpredictable and dangerous, both to divers and marine life, and the parameters involved are too numerous to make it safe. Even dolphin safe frequencies could be harmful with unintended amplification, and putting aside for one moment the cetaceans, the marine habitat is diverse, and finely balanced, there is no way of knowing what effect this system could have on other marine creatures.