Underwater Data Transfer

[jerni2Bfre]

A question to the scuba tek gods,
I'm a student at the Art Institute of Pittsburgh, I am designing a product for scuba divers and diving companies that can seriously reduce some of the risks of diving. The product is lacking proof that a data transfer system exists that can transmit through water. Without the data transfer system that works underwater I can't prove that my idea can work. I have been doing research online looking for any product online that involves any kind of data tranfer underwater but can find nothing that invoves what i'm trying to do. If anyone knows of a product, or can point me in anykind of a direction to a similar product I would be greatly appreciative. Unfortunatly, I am on a tight deadline my design is due for completition on September 22, 2002.
Respectfully Requesting,
M. J.

 

[DiveTub]

why not go and look at the answers from the last post you put on the forum.

http://www.uwatec.com

Chris

 

[viking]

...the only undersea electric-based comm system that I know is public knowledge is the Navy's ELF (Extremely Low Frequency) system. This will be totally useless for your needs because the freqs are in the range of 30 to 300 Hz with a wavelength measurable in miles. Physics of the water molecule in response to EM energy appears to be the main limiting factor. Acoustic systems have a better chance but must have substantial noise filtering capabilities. Discouraging, but it may be worth web-surfing for research institutions who do underwater imaging or tracking to see if they have anything available. It still may be possible if your requirements are small enough... For example, Morse code can be done with a flashlight underwater -- and light is EM energy after all....

 

[Diversauras]

I'm with Sydney Diver, Uwatec transfers from the transducer on the first stage to the wrist mount computer. The question is going to be how far you want the data transmitted.

There are also a couple of U/W transmitter / receivers used for locating the dive boat(or whatever) and they work out to 1500 feet or so, but I don't know about the size of the data string.

 

[FredT]

Encode data in to a frequency swept tone, then send the tone to a transducer. Recover the tone through another 'ducer and route it through a DSP recognition system. Be aware U/W noise level from shrimp and other critters may mask a simple tone. This is standard procedure for most wireless submerged instruments. Range can be several hundred yards, or a few inches, depending on the tone pattern and energy transmitted.

There are books written on how to generate a tone set that is suitable for what your normal range is. Simple digital data can be transmitted with a wake-up pulse, followed by timed 0s and 1s (pulse present/absent in a particular (mili/nanosecond) time slice after the start pulse) to represent the data. Generally the digital code is repeated several times for each data set for error checking. Be aware that data formatting and tone shape are often subject to patent restrictions and/or licensing though.

FT

 

[jrtonkin]

Well, there's several considerations...

How much data,
how fast (bandwidth)
what's an acceptable error rate
how far do you need to send it
does it have to be wireless
is it going one-way or both-ways?
how much power do you have available
how big a "box" can this be.

radio-communication is possible underwater. It's
just not very efficient. The normal sort of frequencies used for airborne radio are bad ones to use underwater. The frequencies that do work well are very-low-frequency ones.

This has two big effects:
first, you can't send data very fast on these frequencies. If all you're doing is sending out a simple "my current depth is x feet" type message, you might be fine; if you want to send maps or other images, it might not be fast enough to be usefull.
Second, the antennas needed for these frequencies tend to be very large. Fancy engineering can get around that to a certain degree, but generally the lower the frequency, the bigger the antenna.

Sound communication works quite well underwater. But there's a lot of noise, so your system has to
be very good at recognizing what's it's own data, and what's background sounds... possibly including another group using the same type of system, that you didn't intend to include in your network.

Optical communication might also be practical, depending on what you're doing. If you can bring the transmitter and the receiver together whenever you need to exchange data, then matching-windows with infrared or even visible-light signalling will go back and forth between them quite well, without the difficulties of building waterproof electrical plugs.

Of course, this has all the problems you normally find with tv-remotes... the two devices have to be close together, facing each other, and it generally only works between two devices at a time.

Obviously, wires and fiber-optic cables work just fine.

Depending on just what sort of information you're looking to transmit, even a purely mechanical system might work.

For examples of existing underwater comm systems, look at Submarine/Naval Radio (uses low-frequency radio waves); Naval sonar systems (sound communication) (the "chirp rate" is used to provide certain information about the detected target; however, it could be used to carry information instead); hoseless air-integrated computers (don't know what they use, I suspect radio); TTL flash control for underwater cameras (visible or with wires), and various slaving methods; the links that surface-supplied-divers use to communicate with their tender (wire, I believe); the various methods used to control ROVs (remote operated vehicles -- used in certain very-deep explorations); etc.

All-in-all, odds are that it can be done... it just may cost more, be less reliable, be slower, or have bigger physical requirements than you want...

Good luck with it,

Jamie