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UWIS - Underwater GPS?

Discussion in 'Public Safety Divers/Search and Rescue' started by SeaWarden, May 19, 2020.

  1. Heka

    Heka Angel Fish

    # of Dives: 100 - 199
    Location: Finland
    23
    21
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    They've been testing the unit in a flooded gold mine where i dive, it does seem to work fine.
    I don't know anything about the unit, only seen graphs of the dives.
     
  2. CuriousRambler

    CuriousRambler Solo Diver

    # of Dives: 25 - 49
    Location: California
    540
    190
    43
    True, but then it's not a one to one comparison of a system with three buoys triangulating a position :D With GPS there's also some intentional jitter in the signals to inherently degrade the accuracy, and some other limited situations where it won't function at all, which all keep it "good enough" for most civilian purposes, but not so good that it's easy to use for nefarious purposes.

    So, pondering on this last night as I was waiting for my puppy to do his business outside, it dawned on me that Bluetooth may actually be the perfect technology for this application. I obviously don't know specifics of their system, but the bluetooth standard is 100mW of power, or 0.1 watt. Let's call the distance from a diver's tank to their hands 60cm just for argument's sake. This is probably conservative, and would definitely be limiting, but play along for now. A 2.4GHz signal with 0.1w source power will be attenuated to ~0.0000000000001153w, or 1.15x10^-13 over 60cm of water. That's an impossibly weak signal, and you'd need an incredibly sensitive receiver to pick anything up.

    But the environment is actually helpful in this scenario. If you had a 1.0x10^-13w signal you were trying to find while sitting in your living room, you'd have absolutely no hope. Bluetooth, wifi, cordless telephones, baby monitors, car alarms, even your microwave oven all use 2.4GHz. There's a ton of interference on the surface. You'd need not only some incredibly sensitive instruments to receive such a weak signal in the first place, but some really fancy discrimination to "see past" all the very loud interference. The same reason I said it can't be used underwater may actually help in this case. Because water is so attenuating to 2.4GHz, you can assume with near certainty that you'll have essentially zero interference at depth, which would actually make it easier to "hear" a very weak signal from a nearby source. You also shouldn't have significant multipath interference issues.

    I still have my doubts that there's enough sensitivity in a receiver to pick up a signal that low, but I'm not as confident it's impossible.

    A somewhat analogous situation: NASA's Voyager spacecraft use 23 watt transmitters. By comparison, a fixed mount marine radio you'll see on a dive boat is legally limited to 25watts. Your Boston Whaler has a more powerful radio than the only human-constructed objects to travel into interstellar space. That's pretty cool. Just as cool; we still talk to them regularly. I had to look this up, but Voyager(s) use 8GHz radio, which is pretty interference free, just as the underwater 2.4GHz situation would be. We can hear the incredibly weak signals coming back from Voyager by using massive antennas (like 100+ft diameter). Voyager 1 is currently 13.8 BILLION miles from Earth, and we still communicate with it precisely because of the low interference. That big FM radio station you can only pick up from the next county on a clear day is transmitting near 100,000 watts, but there's too much interference for a clear signal to carry even a few dozen miles.

    All that to say "maybe Bluetooth could work for them." I still think it's unlikely, but again, I'm no expert. If I'm simply remembering the loss characteristics through water incorrectly, I wouldn't have to be far off for my math to fall apart and render all of my assumptions completely irrelevant.
     
  3. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
    9,344
    7,033
    113
    This is really old, currently inaccurate information. It was called Selective Availability, and was turned off in 2000.
    GPS.gov: Selective Availability
     
    Storker likes this.
  4. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS
    4,651
    1,145
    113
    Ive seen a few units like this advertized over the years. with out knowing anything in its design I have an intimate knowledge in how this type of stuff works. The draw back is that it has buoys and there for the unit is not cost effective unless you have a need for this like rescue units etc. I wish I could remember the last unit like this that had a inner tube with a beacon on it and it communicated with the diver work units. It also allowed multiple surface units to be used. Every one has had power issues. Face it you have a HF transmitter to power. HF dies not travel far relatively speeking but is very directional when it comes to a receiver determining the bearing the sound is coming from. Much like a fish finder being high freq it can then provide a good resolution to the source. To do that you have to have some sort of directional finder incorporated into it to beam form and resolve to a relative bearing and then correct to a true bearing by using a electronic compass on each diver. That also takes power. to then be able to track other divers int the area will require either comms direct diver to diver or via the surface buoy which may be prioritized for a single function. I say that because to work to its best capibility it may require one buy to handle one catagory of data and another to handle say diver to diver position and another to handle comms transmission to divers. There are many configurations that can make this work. But it all has a cost and normally that cost it tremendous if not provided with in a commercial funded operation. I have used many units that provide partial data like this for ship tracking on exercize ranges but they all required external power to operate both the tracked units and the central/reference point beacon
     
  5. CuriousRambler

    CuriousRambler Solo Diver

    # of Dives: 25 - 49
    Location: California
    540
    190
    43
    Funny, we use GPS very extensively at work, often with RTK base stations and/or NavCom Starfire corrected GNSS subscriptions, and this is commonly discussed by one of the physicists I used to work with. It's "Selective Availability," which a quick search shows you're right, Clinton killed it. Funny enough, that bit of knowledge makes a bunch of contradictory puzzle pieces about that physicist's knowledge of the system fall into place. That's what I get for taking the knowledge for granted and not verifying the information myself. Just one more thing to add to the long list of reasons I'm glad I don't work with that one anymore :D
     
  6. Subcooled

    Subcooled Assistant Instructor

    # of Dives: 200 - 499
    Location: Finland
    1,074
    288
    83
    I have used it several times. It works.

    The yellow receiver must be able to see the three sonar buoys, which means that you should mount it on your back - or if the UWIS receiver/transmitter is attached to an underwater tablet (with a map) then you need to keep the device well in front of your. Also, if you turn in such a way that your body blocks visibility to one of the buoys, then your position will jump wildly. You will notice this though and so will your surface support team. Once you learn to use that thing, you can do accurate surveying and perfect your dive site maps.

    A test dive:

    I had to check a number of targets (seen on the side scan sonar image below). Visibility in the river was about one inch. Diving by touch. Hence, my only option was to use UWIS. A rope tender cannot position me as accurately.

    pic1.jpg
    Fortunately, we had some diving gear...

    pic2.jpg

    and so I was guided by phone to the targets. Found them.

    I also tried UWIS in search and recovery diving. The pattern is a bit suboptimal due to some communication problems and some hurry, but my track was recorded...
    pic5.jpg
    You can check the UWIS youtube channel for some better examples.

    I am not affiliated with the company in any way. I have just done some test dives for fun (just like so many other divers here).
     
  7. Subcooled

    Subcooled Assistant Instructor

    # of Dives: 200 - 499
    Location: Finland
    1,074
    288
    83
    It actually does work under water. I've tested it and in the picture below you see it attached to a tablet on a dpv.

    Given the possibly abyssmal visibility, in public safety diving one might consider it more as a tool of the rope tender (or whoever you talk with) though.

    I am not a public safety diver.

    pic3.jpg

    ps. it is well known from e.g. cave radio communications that inductive transmissions (magnetic field only) work differently from electromagnetic radiation: where radio waves cannot penetrate rock, magnetic loop radios (heyphone, molephone and later) will. Don't know about water, but electromagnetic and inductive transmission surely are different.
     

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