GPS underwater

Discussion in 'General GPS Discussion' started by ken mankoff, Dec 4, 2003.

  1. ken mankoff

    ken mankoff Guest

    Does GPS work underwater? If yes, to what depth? What errors are
    introduced?

    My knowledge in this domain is based on hollywood, but I assume "yes"
    because submarines use satellites. But they often surface or raise
    scope implying the answer is "no".

    Any ideas?

    Mankoff
     
    ken mankoff, Dec 4, 2003
    #1
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  2. ken mankoff

    Graham Guest

    I don't generally think of Hollywood as a source of "knowledge"! :cool:
     
    Graham, Dec 4, 2003
    #2
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  3. Water absorbs (or reflects?) the signal.
    For example: you notice this in the woods when is has rained, with all the
    water on the leaves your signal becomes pretty poor.

    I don't know with how many dB/m the signal loses strenght though, but I
    believe that within a meter there is no measureable signal left.

    Vincent
     
    Vincent van der Laan, Dec 4, 2003
    #3
  4. GPS will not work under water.
    Water will block the signal very effectivly, maybe a few centimiters would
    be fine, but I doubt it.

    J;-)
     
    Jesper Lundorf Thusgaard, Dec 4, 2003
    #4
  5. ken mankoff

    Robertwgross Guest

    A GPS receiver *will* work underwater, but the antenna will not.

    In some cases, a GPS receiver can be kept submerged and the floating antenna is
    let out on a long tether.

    In other cases, a GPS receiver is kept inside a sub and the antenna is exposed
    on a conning tower just above the surface.

    ---Bob Gross---
     
    Robertwgross, Dec 4, 2003
    #5
  6. ken mankoff

    Guest Guest

    It doesn't work underwater so subs rely on inertial navigation when
    submerged deep, raising a com buoy on occasion to get a GPS fix, and
    every boat still carries a sextant too.
     
    Guest, Dec 4, 2003
    #6
  7. ken mankoff

    Marcel Guest

    a sextant doesn't work underwather as well.

    :)
     
    Marcel, Dec 4, 2003
    #7
  8. ken mankoff

    Abe Guest

    Sure they do, you've just got find enough starfish to take a reading
    from.
     
    Abe, Dec 4, 2003
    #8
  9. Yeah, but then the GPS reciever will be reading where the *antenna* is,
    not where the sub is.

    Steve
     
    Steven Shelikoff, Dec 5, 2003
    #9
  10. ken mankoff

    Robertwgross Guest

    That was not a restriction of the original poster's inquiry.

    However, if a sub knows its depth (which it does), and if it knows the length
    of the antenna tether (which it does), and if it knows whether it is stationary
    or moving (which it does), then it does not take a rocket scientist to
    calculate the offset between the reported position of the antenna versus the
    true position of the sub. Besides, a sub has IN for primary navigation, and it
    would use GPS only for backup.

    ---Bob Gross---
     
    Robertwgross, Dec 5, 2003
    #10
  11. The original poster asked if GPS works underwater and if so, to what
    depth. Well technically I guess it would work underwater but probably
    not much more than a few inches. When a submerged submarine uses GPS,
    the GPS system isn't working underwater in the sense that it's telling
    the sub directly where it is and what depth it's at. In a car or
    airplane, the GPS alone can provide everything you need to know about
    your 3d position and velocity to some level of accuracy. But as you said
    above, unlike a plane or car, the sub needs to determine it's depth,
    speed and course independent of the GPS system to know it's 3d position
    and velocity... because GPS doesn't work underwater.

    Steve
     
    Steven Shelikoff, Dec 5, 2003
    #11
  12. GPS requires satellites. Satellites, of any sort, do not communicate through
    water. Therefore GPS does not work underwater.

    If the submarine surfaces, or raises an antenna, or otherwise gets
    communication above water, we are no longer "underwater" and the question is
    moot.
     
    Andrew Toppan, Dec 5, 2003
    #12
  13. : Does GPS work underwater? If yes, to what depth? What errors are
    : introduced?

    Yes and no. In commercial and military circles the term
    "underwater GPS" is used, but it is normally included the use of a
    buoy or to collecte the RF signal from the regular GPS system, and
    then accoustic propogation from the buoys to the ultimate reciever.
    "Underwater GPS" is an improvement on traditional accoustic locating
    methods, for example US subs at certain places can emit specific 'pings'
    and get pings back from pre-located buoys or submerged systems.
    Underwate GPS enhances this capability by including clock and ephemeris
    data in the accoustic signal to allow for greater precision location.
    It operates much like GPS (and often interfaces with GPS) but uses an
    accoustic signal to reach the sub.
    Of course, a surfaced submarine (or one with a floating antenna)
    can use 'regular' GPS, but underwater the RF signal can not ordinarily be
    collected.

    regards,
     
    Steven James Forsberg, Dec 5, 2003
    #13
  14. Satellite to submerged submarine communications have been the subject of
    research for some time now. The most promising approach is
    the use of lasers at about 454 or 488nm (blue and blue green). I once
    helped design and build an absorbtion meter to go on the Dolphin. It
    was to measure the absorbtion and scattering of light at the
    aforementioned frequencies. The prime contractor was also building
    a system for the laser comms. That was in about 1990.

    I suspect the desire to spend money on these systems diminished rapidly
    along with the Soviet blue-water sub fleet. Laser comms would be much
    more problematic in nearshore waters with higher particle loads
    (plankton and sediments).
    Mark Borgerson
     
    Mark Borgerson, Dec 5, 2003
    #14
  15. ken mankoff

    Guest Guest

    Wather learned to use a sextant just like everybody else.
     
    Guest, Dec 5, 2003
    #15
  16. ken mankoff

    user Guest

    GPS transmits on 2 freqs, 1575.42 Mhz for civilians and somewhere near
    there for the military. Kinda hard to push that high of a frequency
    through the medium a sub operates in.
     
    user, Dec 5, 2003
    #16
  17. ken mankoff

    wee-meng lee Guest

    I read in the Dummy's book on Submarines (very interesting book btw) that
    the GPS antennaes are located right on top of the conning tower where the
    periscopes are. They only work when the submarines go very near the surface
    which is seldom as they lose their stealth. The inertial guidance systems
    are calibrated and once when it submerges, the GPS no longer works. The
    inertial guidance system then takes over.

    To receive transmissions from base, they use a very low frequency which can
    only transmit simple messages which says something like "message for you".
    They then need to surface so that the higher freq antennaes can work.

    wm
     
    wee-meng lee, Dec 5, 2003
    #17
  18. The word you want is "scatters", no form of the initial wave retains
    enough power to be coherently received. My first editing job at the
    FCC was "Rain Climate Considerations for Planning Satellite Systems".
    Worst area for the tiny drops that scatter most and best is Atlanta.
    That is why all those satellite operations started in Atlanta.
     
    Jack Linthicum, Dec 5, 2003
    #18
  19. ken mankoff

    Guest Guest

    The low frequencies aren't limited to simple messages but just the
    speed and direction. Transmitting antennas in the 150 khz range can be
    as much as a quarter mile in length, fill large fields, and aren't
    always above ground. They're just too big to be carried by the sub in
    a permanent setup, but messages can be sent in simple morse code or
    slower speeds of rttty, etc. Get a good shortwave receiver and you can
    hear lots of signals between around 150-300 khz. The limitation is
    that the messages are from shore to sub only. The band is basically
    license free and sometimes used by experimenters and low power video
    broadcasters too.
     
    Guest, Dec 5, 2003
    #19
  20. ken mankoff

    Jim Watt Guest

    Its not licence free, and you have no chance of transmitting video
    on LF it takes up too much bandwidth.
     
    Jim Watt, Dec 5, 2003
    #20
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