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Why Is It So Difficult to Map the Ocean?

nautil.us

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Re: Why Is It So Difficult to Map the Ocean?

#21

Post by Aerroon »

wheelerof4te wrote: post #9
RcouF1uZ4gsC wrote: post #6

I bet the US Navy has classified ocean floor maps that are far beyond those available to the public. Knowing the ocean floor better than your opponents is likely to be a big advantage when playing the various cat and mouse games with attack and ballistic missile subs that the US and the Soviet Union played for decades.

I doubt it. Most of the ocean floor is very deep, so deep that even modern submarines can't reach it. If I were a non-human, intelligent species, that would be a perfect place to hide.

To add: the test depth for the Virginia-class submarines is 240 meters. The previous Seawolf-class had a test depth of 490 meters.

The average depth of the Pacific ocean is around 4000 meters. The average depth of the Atlantic is about 3600 meters.

Re: Why Is It So Difficult to Map the Ocean?

#23

Post by dylan604 »

123pie123 wrote: post #17
dylan604 wrote: post #13

Earlier quoted context omitted.

Any ship using sonar to map the floor would not be able to do so in secret. The only hope it would have would be to take advantage of just how vast the ocean is. However, sound carries a long long long way, and it would be very difficult to have a ship doing this in secret. Any opfor ship could just tail behind the ship and passively listen to the same signal and generate their maps in secret.

not sure if ths is a daft question or not, but could they just reduce the power of the sonar?

It's hard to appreciate just how sensitive the towed array sonars actually are. The line from Hunt For Red October about a boat off the coast of San Francisco hearing a boat "way the hell out by Pearl" is something that always comes to mind.

One could do some mapping by listening to the reverberations from underwater rock slides and other naturally occurring sources of sounds--if you just so happen to find yourself in the right spot at the right time.

Re: Why Is It So Difficult to Map the Ocean?

#25

Post by dieselgate »

jpm_sd wrote: post #2

Because we have to use sound waves instead of radio waves. But the article is mostly about satellite based gravimetric mapping techniques which are fundamentally low resolution.

No comment on the mapping specifics for this but I always found it fascinating and cool how sound waves move almost 5x faster through water than air.

Re: Why Is It So Difficult to Map the Ocean?

#26

Post by nabla9 »

dylan604 wrote: post #13
RcouF1uZ4gsC wrote: post #6

I bet the US Navy has classified ocean floor maps that are far beyond those available to the public. Knowing the ocean floor better than your opponents is likely to be a big advantage when playing the various cat and mouse games with attack and ballistic missile subs that the US and the Soviet Union played for decades.

Any ship using sonar to map the floor would not be able to do so in secret. The only hope it would have would be to take advantage of just how vast the ocean is. However, sound carries a long long long way, and it would be very difficult to have a ship doing this in secret. Any opfor ship could just tail behind the ship and passively listen to the same signal and generate their maps in secret.

Ocean floor is not mapped in secret. Most of the work is done by non-military government agencies.

US Navy has 7 Pathfinder-class survey ships under Naval Oceanographic Office scanning the ocean.

Re: Why Is It So Difficult to Map the Ocean?

#28

Post by nradov »

nabla9 wrote: post #10
RcouF1uZ4gsC wrote: post #6

I bet the US Navy has classified ocean floor maps that are far beyond those available to the public. Knowing the ocean floor better than your opponents is likely to be a big advantage when playing the various cat and mouse games with attack and ballistic missile subs that the US and the Soviet Union played for decades.

Still not good enough. US Navy subs have underwater collisions from time to time. In 2015 USS San Francisco collided underwater sea mount at full speed. It was supposed to be deep blue sea. In 2021 USS Connecticut collided with underwater mountain in South China Sea. US Navy needs to map ocean floor only to 500 meters to keep it safe for submarines but they can't even do that.

The US Navy reports from the 2005 (not 2015) USS San Francisco and 2021 USS Connecticut groundings can be found here. In both cases primary blame was placed on the crew, although charts were a contributing factor.

https://www.cpf.navy.mil/FOIA-Reading-Room/

Re: Why Is It So Difficult to Map the Ocean?

#30

Post by bradrn »

I do research on oceanic lidar. The basic problem is that light is absorbed and scattered by water, to a far greater extent than it is by air. Thus, even though we have no problem seeing through hundreds of kilometres of air, even a kilometre of water is sufficient to filter out nearly all light [0].

In practical terms, this restricts the ability of lidar systems to detect features underwater. As a general rule of thumb, in the very clearest oceanic waters, a lidar has a maximal range resolution of roughly 70 metres. Naturally, this low range becomes further degraded in coastal waters, which are more turbid. Thus, lidar — the best method we have for mapping land — is basically impossible to use outside shallow coastal areas, and we have to rely on more difficult methods such as sonar (about which I don’t know very much at all).

If you want to learn more about this stuff, I can highly recommend [1] — a free and remarkably comprehensive reference on ocean optics (which turns out to be a surprisingly large and useful field).

[0] https://en.wikipedia.org/wiki/Aphotic_zone

[1] https://oceanopticsbook.info/

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