Navy adapts laser cannons to chat with stealth subs

Talking to submarines is a very a tricky business - most communication systems are based on radio or acoustic signals, but neither travel very far in water. This means that to pick up radio signals, submarines must surface or raise communication buoys very close to the surface, neither of which are appropriate for nuclear-powered stealth submarines that remain deep underwater for months at a time.

i-466d08f7d740a47c7295e6a4f2eb9f4a-300px-Clam_Lake_ELF.jpg

Radio operators can overcome the problem of poor signal penetration by using giant arrays broadcasting in extremely-low frequency ranges, but these are expensive, difficult to build, and massively energy-intensive. The Russian ZEVS system operates at 82Hz, corresponding to a wavelength of 3658.5km - more than half the radius of Earth! Normally signals are transmitted using an aerial corresponding to half the wavelength of the signal, but in the case of ELF systems, such an aerial would stretch from New York to Omaha. Instead, a site with extremely low ground conductivity is found and two electrodes sunk into the ground, some 60km apart, in effect using Earth as part of the aerial. Then a dedicated power station must be built to supply the array. The result - signal that can broadcast just a few characters per minute at several watts, heard the world over. The system is so expensive and impractical that only two countries have ever built ELF arrays - the Soviet Union and the United States of America.

i-af5180bb8ae28c36c869d75688dd92a8-CC_Mateus_272425.png

However, physicists at the US Naval Research Laboratory in Washington are proposing a relatively cheap and portable alternative: laser cannons. A team led by Dr Ted Jones used flashes of intense laser light to superheat small packets of water. The resulting steam explosion generated a 210 decibel acoustic pulse - louder than a jet taking off at 25ft. The researchers hope to develop the laser cannon to encode information in the acoustic signal. Because the laser can travel hundreds of metres through clear air, the technology could be mounted on aircraft to talk to submarines below the surface.

By studying the reflected sounds of the steam explosion, the technology could also be used by ships and submarines to gather information on underwater environments, from detecting mines to mapping the seabed. Jones will present the research later this month at the 157th meeting of the Acoustical Society of America in Portland, Oregon.

All of which leaves only one problem with both the ELF and laser communication systems: although the Navy can chat to their submarines, the submarines can't talk back. Any bright ideas, SciencePunk readers?

More like this

Caitlin O'Connell-Rodwell is Co-founder/CEO of Utopia Scientific and an instructor in the Department of Otolaryngology at Stanford University in California. Research in the O'Connell-Rodwell laboratory focuses on communication through vibrations in large mammals. In a previous blog, I discussed Dr…
This post is written in response to the contest I posted on my Twitter feed earlier today: SciencePunk challenge: give me two unrelated topics and I will attempt to write a blog post combining them. Your time starts now. Of several excellent and perplexing replies, I decided to seize the gauntlet…
What's the application? Measuring the distance from the Earth to the Moon by bouncing a laser off one of the retro-reflector arrays left there by the Apollo missions. What problem(s) is it the solution to? 1) "How does the distance from the Earth to the Moon vary over time due to things like tidal…
The third category in our look at lab apparatus, after vacuum hardware and lasers and optics is the huge collection of electronic gear that we use to control the experiments. I'll borrow the sales term "test and measurement" as a catch-all description, though this is really broader than what you'll…

All of which leaves only one problem with both the ELF and laser communication systems: although the Navy can chat to their submarines, the submarines can't talk back. Any bright ideas, SciencePunk readers?

Fire off a missile with a sky-writing package...
(I think that featured in a movie - 60's Batman perhaps)

Or more seriously - drop a message carrying buoy which can manoeuvre away from the sub's immediate area, then surface and 'squirt' the reply.

Or more sneakily - add arrays that can replicate whale calls and hide the message in the fake calls...making sure that the call isn't a) alluringly female, and b) not sent during the mating season.

Uh, speaking of whales and other marine mammals, wouldn't a 215 dB wreak havoc on echolocation and communication for anything nearby? And wouldn't such a sound act like fishing with dynamite?

By natural cynic (not verified) on 12 May 2009 #permalink

I like the whale calls idea, Eamon. Alternatively, how about sitting on top of a trans-Atlantic telephone cable, and using electromagnetic induction to signal down it?

I like the whale calls idea, Eamon. Alternatively, how about sitting on top of a trans-Atlantic telephone cable, and using electromagnetic induction to signal down it?

Actually you're not far from the truth - acoustic communication with submarines uses hydrophones attached by long undersea cables to base stations on land.