Underwater Data Communications

For me the best solution would be an anchored buoy just above your underwater devices. An umbilical cord carrying power and signals to the device (or ultrasound - that would be wireless) would collect the data. On buoy there is a transmitter in short wave range (all ranges from 4 MHz to 24 MHz have oceanic data communications bands with a bandwidth of 3000 Hz (allotted to 10 channels) , more than enough for your application.

I build such a system some 30 years ago and it worked very well.

the beauty of this design is that you can have a solar panel or a windmill on the buoy to power the whole shebang.

They're only 100 nanometers offshore? (Sorry, I couldn't help myself).

If it's really 100 nautical miles, you'd have to use radio.

Have to agree with above. Have installed many current meters and other devices using the same method. Even using sat transmission.

Need to be aware of potential for damage from shipping. Large visible buoys create too much drag especially with the length of subsurface cable you're running. Something underwater with a surface antenna would be susceptible to damage by traffic.

The big boys (Russia and the USA) use very low frequency radio to talk to subs still underwater. Data rates are slow.

I am sure a web search will help with frequencies and methods......if that way interests you at all.

And the antennas are dang near a mile long too. And you're lucky to get 10 baud out of them.

The navy is currently researching the use of lasers for u/w communications. I can't find the link but try google, it should be there.

There was some "what if" type discussion back in the 1980's about using Blue/violet/UV lasers to communicate with subs from satellites, but there were severe limitations in depth. There was also the issue of cloud interference and the possibility that the Soviets might be able to figure out in a general sense where our subs were based on reflection from the wavetops. The plan died in it's infancy. They went with ELF in it's place. ELF is such a low bandwidth medium that the Navy uses it mainly to instruct subs to come to periscope depth so that they may receive a satellite signal with more information. the amount of data they can send over the ELF link is very limited.

http://en.wikipedia.org/wiki/Extremely_low_frequency

http://en.wikipedia.org/wiki/Communication_with_submarines

http://www.mwjournal.com/journal/article.asp?HH_ID=AR_7340

He does not need the distance that one will get I am sure......

Model radio control of submarines is possible and they use relatively high frequencies. I have not studied all the details but it does work to a depth of a few meters I believe.

So surely a frequency, somewhere between the two extremes, with slightly more practical lengths than 1 mile might be found that can reach the distance/depths required?

If that nm means nautical miles, a sonar powerful enough to give reliable communications is going to disrupt if not kill all sorts of wildlife, and require a LOT of energy to operate! Look elsewhere!

TS, that is probably the best answer I've seen on this thread. GA my man!

Thanks. This thread is right down my alley. Actually, I am engauged in geophysical research rather than oceaneering but I hope I steered Mupwi in the right direction. By the way Mupwi, you may want to contact Underwater Surveys located in Mulzenburg next to Cape Town. They may be able to help you as well.

Tel:+27 (0) 21 709 6000

info@underwatersurveys.com

Underwater Surveys.com

GA

Just one point: if the surface buoy is anchored to the bottom (and I guess it must be), then, why not anchor it to the same weight holding the bottom equipment down. Comms. from the bottom to the surface can then be wired (but the anchoring system then needs to be something which will not allow excessive twist).
The bottom equipment can also then be powered by the solar collector and battery on the surface.

Mupwi,
Are surface buoys acceptable in the proposed locations?

Yes Randell, you are also correct as having the seabed package attached to the surface buoy is another way of deploying the instrumentation package. It would eliminate both the acoustic modems and the acoustic release as RS-422 serial data from the seabed could be run along the anchor chain to the surface buoy . Some wave motion can be absorbed by using shock absorbers between the surface buoy and the seabed.

Not knowing the type of sensors being deployed, I opted for the configuration where the sensor package was immune to wave motion exerted on by the surface buoy as well as the possibility of the sensor package being dragged along with the surface buoy should it be struck by a surface vessel.

There can be allot of time, money, effort, and reputation invested in a system so it is imperative that it is done correctly the first time. For a reliable and successful deployment, one needs to consult with those who design, manufacture, and deploy these systems.

Thanks Randell for your observation and for the GA.

Here is some info that you may need. This link will take you to a listing of Marine Consultants located in Durban.

Durban Marine Consultants