When you consider navigation, the most common tool for everyone will be GPS. It is great if you are out walking, driving, flying, or boating. For those of us that enjoy SCUBA diving or driving a submarine though, we might be out of luck.
GPS will not work underwater, except in some very niche cases.
There are two primary issues with using GPS underwater. Primarily, GPS signals do not transmit well through water, and secondly, GPS receivers are not waterproof.
The exception is that, if you are only a short distance under the water, and you have a waterproof receiver, then you might be able to use GPS.
Although the signal from the satellite will be absorbed by the water, it does not instantly stop at the air/water transition. The interruption in the path of the signal, however, will dramatically affect the accuracy of your position.
Some GPS receivers can work underwater
A waterproof, standard handheld GPS unit, might work underwater if you are looking to navigate or give coordinates for a spot on the ocean floor.
Underwater, its battery life may not be as long, but waterproof cases can serve as perfect substitutes for non-dive specific models depending on your intended use case and battery life needs.
Unfortunately, however, the signals from GPS satellites are so weak by the time they reach the surface that they are not going to propagate to any significant depth.
This means that a standard, waterproof GPS, while possible to use near the surface, is not going to be a reliable way of navigating underwater.
Can you use GPS when diving?
There are some models of GPS which are marketed as suitable for diving.
Essentially, they will receive GPS signals when above the surface, and then switch to another navigation method underwater.
When used correctly and with care, underwater navigation can be remarkably accurate (within 20m) – which is within diving limits at most depths.
These units work just like their above-water counterparts, except they don’t receive transmissions from satellites when underwater. Instead, they use pressure and inertia to calculate their position and have to surface to get an updated fix periodically.
When you are diving and want accurate data regarding depth, position, etc., these models can be used, but you must understand their limitations.
They provide accurate information when stationary or moving at a constant velocity. Otherwise, they start to work off a drift rate or location offset that changes based on your behaviour. For example, surface intervals, drift while moving, turns on ascent/descent etc.
If you plan on recording locations while diving, these factors must be considered when using your handheld unit and then corrected post-dive, using calculations based on speed/time of ascent/descent.
Does salt water damage GPS receivers?
As with all electronic equipment, salt water can damage GPS receivers.
If you want to use a regular GPS at sea, such as the one on your phone, you should consider waterproofing to guard against salt water damage.
The fact that you’re in water doesn’t impact your ability to use GPS, and your cell phone will still be able to connect with satellites and determine your location.
Electronic manufacturers are aware of salt’s effects on their products, so many devices and appliances for marine environments come with built-in protective measures, often including warning labels to let users know what precautions they should take.
If you want to double-check on a specific device before taking it into salty waters, however, you should contact the manufacturer for advice on how best to protect your device.
Can GPS work at great depths?
When you get to any significant depth, GPS will definitely not work.
That said, modern underwater vehicles-like remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs)-have been equipped with other navigational equipment instead.
For example, they carry sophisticated sonar systems, inertial measurement units (IMUs), compasses and gravity sensors that combine to give reasonably navigational accuracy.
On the surface, they use GPS to get an accurate position fix. Then they submerge and switch across to the inertial systems to maintain a rough idea of where they are.
The longer a submarine is submerged, the further the inertial fix is likely to drift away from the true fix.
Only once the submarine surfaces again will it be able to update its fix using GPS.