[PSUBS-MAILIST] Underwater Navigation

[Alan via Personal_Submersibles]

River,
thanks for that, you obviously know this stuff.
A few more thoughts have come to mind on my system, appreciate your thoughts.
We could use 3 or 4 off the shelf transducers from a depth sounder system,
hung 10 meters below buoys. Each having their own electronics enclosure,
with GPS & electronics to transmit the GPS data acoustically to the submarine.
The submarine transducer receives the signals which are analysed for their
distance & GPS position then trilaterates it's GPS position based on these &
it's depth. This GPS position is fed to the off the shelf boat chart plotter so we 
can visualise our position on a bathymetric chart, & chart our dives, logging way 
points of interest. We can also print out data on return.
The subs GPS coordinate can be transmitted to all the buoys ( in case one is closer
than the others) and this can be transmitted to the support boat.
The cost would be 4 buoys, 5 transducers, batteries, maybe 5 arduinos or
Similar, & a chart plotter. ( & hours of electronics & coding)
I like the idea of transducers hung under the water as there is less chance of
the signal being obstructed than with a seabed based system.
It could be a plug & play system that could be shared among subs.
Alan



> On 1/09/2019, at 9:45 AM, River Dolfi via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> That type of system, with several transponders with known location communicating with the submersible is known as a "Long Base Line" system, or LBL. That was the state of the art before GPS. Typically, dynamically positioned drilling rigs would hold themselves on position based on feedback from LBL transponders installed on the seafloor (often by manned submersible) providing more reliable and accurate positioning than Loran C was capable of. Now you would just use GPS.
> 
> Today, Universal Short Base Line (USBL) systems are more common. A surface mounted hydrophone unit transmits an activation ping to an smart beacon attached to the undersea item to be tracked. Upon receiving the activation ping, the beacon transmits a timestamp and a depth back to the surface hydrophone. Using a reference speed of sound in water, the total travel time of the signal, , bearing of the signal, and the depth reported by the beacon, the topside unit can calculate the relative position of the subsea beacon (or multiple beacons) which can be interfaced with a GPS receiver on the topside unit, and provide a UTM coordinate and depth for the subsea item to be tracked. 
> 
> This is all fine and good for tracking an ROV, where the operator and the surface unit are at the same location. Navigating a sub using a USBL system requires specialized acoustic modems to transmit the UTM data back down to the submersible, and then some type of computer to display it all.
> 
> There is no need to mention how ludicrously expensive (and heavy, and complicated, and delicate) all of this equipment is.
> 
> One of the biggest unresolved problems on Psubs is navigation, inertial navigation and anything acoustic based is entirely too finnicky and complicated.
> 
> I think the most practical navigation tools available to amateur submariners would be a basic heading indicator (magnetic or airplane gyro compass) and some of the really nice commercially available fishfinder/sonar units available.
> 
> The bathyscaphe crews in the 60's used to sink a number of labelled 55 gallon drums filled with concrete in a grid pattern around the projected dive area. If you can locate yourself within the grid of barrels using sonar, you have a reference frame to navigate from.
> 
> I propose creating a series of sonar reflectors anchored to the sea-floor. Attached to the anchor could be a trawl float with a specific number or pattern of sonar reflectors attached. Think of day markers on a ship. Each reflector station could be located, and identified, by a fishfinder at a moderate distance. The position of the sub could be fixed by knowing heading, bearing to a specific reflector station, and the approximate distance to the station.  
>   
> Galvanic timed releases can be obtained for cheap, and used to retrieve the trawl floats and sonar reflectors after a predetermined period of use.
> 
> A typical PSub outing could be covered by 3-4 sonar reflector stations, and there is no need to standardize on expensive equipment.
> 
> -River J. Dolfi
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