> Radar is useless underwater, light would also be useless for spotting anything in time to react at speed, and sonar isn’t routinely used because it compromises stealth.
Any people with knowledge in the field care to comment on whether it's feasible for a light (em?)-type, active, near-range detection system to work?
It seems to me the basic problem is:
- enough energy to get a signal at a range sufficient to move around any detected obstacles
- high enough dissipation in water to minimize range at which detection by external sensors is possible
Presumably it's essentially clear of suspended particles, most of the time.
Think driving in fog
To clarify: I mean that, generally speaking, the presence of 'cloudy' water would presumably signify that the seafloor was close. In the open ocean, maybe a sea mount is surrounded by essentially a cloud of particles.
Edit: I think your reply made the thread reach maximum depth, so I'll end it here.. I should do more reading on the topic.
The world's militaries have invested a great deal of time and money into researching underwater sensors. The solution is not going to be discovered by random people on the Internet.
I'm fairly certain someone knows a number of things that have been discovered by random people on the internet.
https://commons.wikimedia.org/wiki/File:Absorption_spectrum_...
I’m not in the field, but I follow it enough to say: in theory, yes, (blue-green lidar), and there is a lot of work on moving this from theory to practice.
But approximately everyone is working on it (for bathymetry and for detecting subs, and similar blue-green laser tech for underwater comms), so its likely once its deployed so that a sub could in principle use it as a “headlight”, it’ll raise similar concerns to sonar, because if it is used actively, passive sensors looking for active use will also be common.
Submarines are optimised in everything for absolute stealth, up to the point that the crew may not make any noise, like dropping a wrench.
We also have highly classified models of the exact shape and mass distribution of the Earth, as this is essential to accurate long-range ballistics (i.e. for ICBMs to hit their targets) -- it affects the gravity experienced over the course, and the precision/accuracy needed is higher than just uniform-density sphere or oblate spheroid. Also of magnetic and other anomalies since that can be used as a baseline when searching for submarines or ships using magnetic sensors, although I think this is less important now.
“Maybe it would help to have a map of the space we’re going to be driving very large, very expensive, strategically important pieces of equipment (that also have crews) through blind” is not, as it turns out, something that never occurred to the Navy.
Project goal is 2030.
Also, fishing trawlers, whales, etc.
Or whiskers! That's how cats and catfish do it. A dozen 300' plastic prongs protruding frontward.
Or, to combine the two : TENTACLES!
How could it not be in the chart though? Is the ocean not fully mapped?
In the specific case of the San Francisco, because notations indicating a probable seamount were not transferred from other charts when the chart being used was compiled; there is some lack of clarity on how much the failures involved are the responsibility of the command crew of the sub and how much of higher command, but its definitely a failure to appropriately use existing information, not a “the information did not exist” problem.
While the area was apparently not well charted, the responsible crew not using the information at hand (including information as to the the quality of charting data for the area) was also apparently at play in the Connecticut grounding.
But sonar and detecting changes in gravity (caused by the higher density of the seamount) aren't.
The seamount should have been detectable.
Gravity detectors work from moving aircraft (it's a common method of deployment), so motion's no problem and can be made incredibly sensitive—sensitive enough to suit the job in hand (place one on a table and then on a book on the table and you'll easily read the difference in gravity). Moreover, seamounts are incredibly large objects and would have huge signatures and thus easy to detect.
I'd suggest the real issue around this matter is that it'll be classified.
We'd have difficulty in fitting LIGO in a sub methinks and seamounts are static and thus no G waves. You're right though, I should have been more specific, perhaps a more understandable description would be a mass detector or sensor.
I reckon the reason we don't hear much about this subject and the reason it's likely classified is that's its primary purpose would be the detection of other subs, detecting seamounts a secondary benefit.
AFAIK, the first sub-deployed gravity gradiometers were developed for the Ohio-class ballistic missile subs and Los Angeles-class attack subs like San Francisco don’t, AFAIK, have them.
Can't they use the same frequency/waveform as whales?
Or a different question: why don't whales routinely hit underwater volcanoes?
a) whales don't tend to go where volcanos are. Whales dive to find food, and their food sources aren't near the seabed. I think the deepest diving whale species are sperm whales, and they go after squid, which are not typically found near volcanos.
b) it's not a question of matching frequency with the whales, it's a question of noise emissions and the amount of energy you're putting into the water. Modern active sonar systems are incredibly energy intensive, and the technology to modify the waveform and limit the power of the waveform to match something biologic doesn't really exist, and would have to justify all the added complexity
c) USN and US geological survey charts are really really good, and regularly updated, to the point where "It wasn't on the charts!" is a claim met with extreme skepticism. 9 times out of 10 some sort of navigation or systemic error was involved.
Seamounts don’t give off active emissions (except maybe if they are erupting), and subs usually use passive hydrophones (which rely on the active emissions of targets), not active sensors when operating underwater to avoid detection.
Navigation is done by charts using inertial navigation alongside dead reckoning. Hitting a mountain is generally because the mountain wasn't on the chart being used, though in principle in could also be due to an error in positioning (with inertial navigation, that should be much rarer than with dead recknoning alone, but its not impossible.) (In the case of the San Francisco, for instance, other charts had a notation of "discolored water" which suggested a probable seamount, which the investigation noted should have been transferred to the chart in use, but was not.)
> Are light, radar, and sonar still not enough to detect obstacles that big?
Radar is useless underwater, light would also be useless for spotting anything in time to react at speed, and sonar isn’t routinely used because it compromises stealth.