GPS underwater

  • Thread starter Thread starter ken mankoff
  • Start date Start date
K

ken mankoff

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
 
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
Click to expand...

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
 
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;-)
 
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---
 
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
Click to expand...

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.
 
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.
Click to expand...

a sextant doesn't work underwather as well.

:-)
 
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.
Click to expand...

Yeah, but then the GPS reciever will be reading where the *antenna* is,
not where the sub is.

Steve
 
Steve said:
Yeah, but then the GPS reciever will be reading where the *antenna* is,
not where the sub is.
Click to expand...

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---
 
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.
Click to expand...

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

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.
 
: 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,
 
GPS requires satellites. Satellites, of any sort, do not communicate through
water. Therefore GPS does not work underwater.
Click to expand...

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).
If the submarine surfaces, or raises an antenna, or otherwise gets
communication above water, we are no longer "underwater" and the question is
moot.
Click to expand...

Mark Borgerson
 
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.
 
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
 
Vincent van der Laan said:
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.
Click to expand...

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.
 
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.
Click to expand...

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.
 
The band is basically
license free and sometimes used by experimenters and low power video
broadcasters too.
Click to expand...

Its not licence free, and you have no chance of transmitting video
on LF it takes up too much bandwidth.
 

Members online

No members online now.
Total: 35 (members: 0, guests: 35)
Back
Top