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Is that possible?

03/15/2009 9:21 AM

Is that possible any of the communication device or system can function under the depth 4000m in sea?

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#1

Re: Is that possible?

03/15/2009 2:35 PM

YES

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#2

Re: Is that possible?

03/15/2009 2:45 PM

Yes. Submarines do pretty well talking with the rest of the world (and seeing where they are going using sonar). There are fibre-optic data and communication cables layed in trenches connecting different continents together, hence you are able to see my posted response (unless some of the bits leaked out in transit).

What is the application?

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#3
In reply to #2

Re: Is that possible?

03/16/2009 1:01 AM

Submarines do indeed use sonar as aircraft use radar, to see where they are going, or see around themselves.

Undersea cables don't count for submarines, or communication under the sea, because they transmit data from continent to continent; AFAIK they are not designed with little substations that transmit & receive from undersea vessels.

But if the issue is submarine vessels communicating with the rest of the world, which is how I interpret the OP, then that typically means electromagnetic radiation. And there are severe limitations on that, because sea water is conductive, which means it attenuates the strength of an electromagnetic field traveling through it. Specifically, the absorption is inversely proportional to the square root of frequency, through a phenomenon known as skin depth.

That means that the lower the frequency, the farther it goes before the signal strength is too low to be usable. Here is a quantitative example of how this works. It's a long story, but at the end you will understand the limitations, so I hope it's worth it.

But first, no you aren't going to get useful communications 4 km under the sea. That's not even a normal submarine, that's some kind of bathyscape, and you should be able to use fiber optics strung in parallel with your bathyscape to mother-ship tether.

At 4 km under the sea, the attenuation of even the very low frequency signals discussed below would be attenuated to levels well below the ability of any radio to receive. I worked out the attenuation at 4 km under the sea, at 10 kHz, and it's over 10,000 dB! There isn't enough power in the world to overcome that much attenuation.

Here's the real world.

In the bad old days of the Cold War, submarines and their sea-launched ballistic missiles provided one-third of the Triad of Mutually Assured Destruction (MAD) between the USA and the USSR. The other partners were manned bombers and intercontinental ballistic missiles.

The advantage of submarines was that no one knew where they were, and the deeper they sailed, the harder it was to find them. If you needed to tell them to launch missiles, you wanted to be able to do that without the submarines having to be too near the surface.

Submarines were contacted via very low frequency (vlf) 14 kHz to 30 kHz radio links. Consider that the bottom of the AM broadcast band in the USA is 530 kHz, and in Europe, 150 kHz. So you are looking at an order of magnitude lower frequency spectrum being used, so that it could penetrate deeper into the ocean.

In the late 1950s and 1960s, the USA's main such submarine was the Polaris class. That submarine had a vlf radio designated the AN/BRR-3, a fully operational specimen of which I happen to own. I have measured its noise figure, and it is 1 dB. Noise figure is a measure of how perfect a receiver is. A perfect receiver (unrealizable) would have a noise figure of 0 dB. So this receiver is within 1 dB of perfection, and there would be no point in trying to make it marginally better, because 1 dB of improvement wouldn't mean much in increased depth.

The sensitivity of that receiver was classified at the time, because if you knew the sensitivity, then you could figure out fairly accurately the maximum distance below the surface the subs were traveling, because skin depth is strictly a function of sea water conductivity, which is easy to measure. The only other variable involved is antenna gain, and that can be bracketed fairly easily if you know what kind of antennas are being used.

Now the sensitivity and the noise figure are two separate entities, but they are not independent of each other. The sensitivity of a radio is defined by how much above the noise floor the signal must be in order to get a certain quality of reception. The noise floor is given by:

noise floor (Watts) = kTBF,

where,

k = Boltzmann's constant, which is the ideal gas law constant divided by Avogadro's number,

T = radio receiver front end (first mixer) temperature, in units of Kelvin (absolute temperature),

B = bandwidth, in units of cycles per second, or Hertz (Hz), and

F = noise figure, which is a ratio without units.

Looking at that equation, for a given noise figure (which as we saw above was already optimized), all you can change are the bandwidth and temperature. Boltzmann's constant is just that, a fundamental physical constant.

The AN/BRR-3 operated at ambient (room) temperature, and there were three selectable bandwidths. I'm not home right now, so I can't check precise bandwidths, but the top bandwidth was under 200 Hz.

That is way too low for voice communications, which requires at least two kilohertz (and that sounds somewhat nasal). The AN/BRR-3 baseband output (what would normally be audio for a broadcast band radio such as AM or FM or shortwave) was instead data fed to a teletype machine. The teletype would spit out the instructions for launching Armageddon.

So we have come almost to the end, and to the point of the story. In order to maximize the depth at which the submarines could communicate, they were forced to use very small bandwidths that were unsuitable for voice communications. If you remember getting your internet connection over a telephone modem, you should be able to appreciate that limiting bandwidth to less than a tenth of the voice bandwidth is a huge limitation for anything other than very specific and limited instruction sets, such as "Launch missiles at target X immediately."

You may be wondering how I came to own one of these receivers, and why I know so much about it, and am willing to share the info.

It's no longer classified because newer receivers use cryo-cooled front-ends, which greatly increases their sensitivity and renders the AN/BRR-3 and radios like it obsolete. I bought mine at a surplus electronics outlet for $600, and that included the classified instruction manual...

So now you have the rest of the story, as the late, great Paul Harvey would have said.

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#5
In reply to #3

Re: Is that possible?

03/16/2009 9:23 AM

can the GPS system function in a depth 4km for the sea level?

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#7
In reply to #3

Re: Is that possible?

03/16/2009 10:05 AM

Excellent answer!

Going back to thinking he needed an audio communications solution, wasn't there an old audio system for sub to sub? i think it was called a grundig?

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#16
In reply to #3

Re: Is that possible?

03/19/2009 8:56 AM

Off subject here, I always wondered what was the process for determining when classified information became common knowledge. In the case of submarines I have knowledge of different unique propulsion designs. One that I have read comments from the skipper at decommissioning ceremonies, was the Narwhal, 71 boat it had a direct drive low speed steam turbine for propulsion. He stated that at the ceremony so I feel free to quote him. I wonder to what depth that turbine design has been de-classified the reactor was unique as well at the time.

I also wonder if the Jack or the NR1 et al, have been de-classified and to what extent. I no longer hold a secret clearance but realize the obligation doesn't go away with age.

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#4
In reply to #2

Re: Is that possible?

03/16/2009 9:12 AM

now i'm working for my design of the autonomous undewater inspection robot. its function to do inspection to the pipeline for the oil and gas industry under 4000m from sea level. i just wonder to have a communication system which have high speed data exchange with the ground.

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#10
In reply to #4

Re: Is that possible?

03/16/2009 2:59 PM

If you want high speed communications, I think you are left with either an umbilical cable connecting the robot to the ship, or a special wireless communication system (which may exist, but I don't know who may sell it).

This is not really a project you can "put together" by your self without a lot of very specialised knowledge and experience in a number of fields. You also mention "autonomous" (requiring an even MORE complex design for a deep sea inspection robot).

Does anyone in the oil and gas industry here know of a company that specialises in this sort of thing and has these robots available for lease or sale? (no use reinventing the wheel)

I would also suggest an internet search.

Are you a student doing a project, or a consultant designing a solution for a project (or tender)? From your comments it sounds like you really don't have much experience in this field at all (hence will require far more detailed answers, hence we need more information to answer).

Please provide more information.

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#11
In reply to #10

Re: Is that possible?

03/16/2009 10:56 PM

you are right, i'm just into this field for only 3 months in this petronas oil and gas company. my previous jod was a maintnance engineer in a lime and stone field. so what you think everything must come back to square one.sori for disturbing you guys, i really appreciate your guys help!

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#12
In reply to #11

Re: Is that possible?

03/16/2009 11:33 PM

That's quite a leap. Can you provide more information on exactly how you want the robot to be operated and what it needs to do? Do you have a specification you could post here?

The more information we get, the less guessing we have to make (and the more focused the answer we can give). Don't be shy with the details.

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#13
In reply to #12

Re: Is that possible?

03/17/2009 9:31 AM

well this the task, im asking to design the autonomous underwater inspection robot that will be used for welding and leakages inspection under sea level approximately 4000m . i choose titanium alloy as a structure body of the robot. then the sensor for inspection part i use the infrared scanner, liquid leakage sensor, and the CCD line scan camera. well for the navigation part i use the RFID system,ultrasonic sensor, proximity sensor, and vector sensor. i not sure the things i add to the robot suit or not? pls add some comment where there is a mistake. thanks

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#14
In reply to #13

Re: Is that possible?

03/17/2009 2:44 PM

OK, so your looking at designing either a AUV (autonomous underwater vehicle)

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

or possibly a ROV (remotely operated vehicle)

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

A google search of "oil and gas pipeline inspection auv" and "oil and gas pipeline inspection rov" came back with a lot of information, including actual designs, products and sensor and inspection solutions.

Here are some examples of existing designs of deep sea AUV's suitable for oil and gas pipeline inspection to give you some more ideas on what you need to include -

Alister 3000

http://www.offshore-mag.com/display_article/253450/9/ARCHI/none/none/1/Alistar-AUV-on-track-for-inspection-trials-in-the-Gulf-of-Mexico/

HUGIN 4500

http://www.km.kongsberg.com/ks/web/nokbg0240.nsf/AllWeb/B3F87A63D8E419E5C1256A68004E946C?OpenDocument

REMUS 6000

http://www.km.kongsberg.com/ks/web/nokbg0240.nsf/AllWeb/F0437252E45256BDC12574AD004BDD4A?OpenDocument

etc.

As this is such a specialised field I would suggest you have a look at all the information available on the internet you can get your hands on to increase your general knowledge in the areas necessary for such a complex project.

Don't forget to keep us informed on how its going.

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#15
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Re: Is that possible?

03/17/2009 11:49 PM

thank man ! is quite a useful information for me!

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#6

Re: Is that possible?

03/16/2009 10:01 AM

You are facing some serious challenges.

Most of these devices are tethered, mostly for power, so running a command link along the power cable is easy.

I think most of us assumed you were looking for voice communications, so perhaps we could return to emc_c post and consider a low frequency digital data stream. But I think perhaps even if you can get the link to work, your lag is going to look like talking to a remote on the moon.

I strongly suspect there may be a commercial solution out there somewhere - but it will not be RF based for the reasons emc_c stated.

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#8

Re: Is that possible?

03/16/2009 10:45 AM

OH, and the GPS - no.

raindrops on a GPS antenna will shut it down. 4,000' of water is a promise.

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#9

Re: Is that possible?

03/16/2009 12:25 PM

what sensors should i added to my underwater inspection robot for checking the leakage and welding joint of the oil pipelines?for the material selection is the titanium alloy affort the high pressure under the sea 4KM?

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