[HN Gopher] Why Is It So Difficult to Map the Ocean?
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Why Is It So Difficult to Map the Ocean?
Author : Brajeshwar
Score : 45 points
Date : 2023-11-11 16:21 UTC (6 hours ago)
(HTM) web link (nautil.us)
(TXT) w3m dump (nautil.us)
| jpm_sd wrote:
| 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.
| emmelaich wrote:
| You can use laser, but that's only good for up to around 50m
| deep.
|
| https://www.dst.defence.gov.au/innovation/laser-airborne-dep...
| dylan604 wrote:
| that's not very useful for the task then is it? maybe along
| shorelines, but that's not what needs mapping since it's
| already been covered in details.
| Groxx wrote:
| Yeah, that kinda sounds like the equivalent of "this tool
| maps land perfectly unless there's a tree or snow within
| sight".
|
| Not useless, but far from a solution.
| dieselgate wrote:
| 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.
| ipunchghosts wrote:
| Synthetic aperture sonar is a massively underrated technology for
| undersea map making and remote sensing.
| _dain_ wrote:
| well it's all underwater innit
| RcouF1uZ4gsC wrote:
| 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.
| wheelerof4te wrote:
| 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.
| Aerroon wrote:
| 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.
| nabla9 wrote:
| 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.
| runeofdoom wrote:
| Were the collisions due to mapping error or human error?
| Afaik, the USN hasn't said.
| virtue3 wrote:
| To be honest; that is actually a pretty dramatically good
| operational excellence.
|
| I wouldn't be surprised if the uss connecticut was a
| resolution issue with the mapping system. And also I think it
| might be hard for the USN to get accurate maps of the south
| china sea currently.
|
| "San Francisco's captain Commander Kevin Mooney was
| reassigned to a shore unit in Guam during the investigation
| of the collision. The Navy concluded that "several critical
| navigational and voyage planning procedures" were not being
| implemented aboard San Francisco, despite Mooney's otherwise
| remarkably good record. Consequently, the Navy relieved
| Mooney of his command and issued him a letter of reprimand."
|
| "The seamount that San Francisco struck did not appear on the
| chart in use at the time of the accident, but other charts
| available for use indicated an area of "discolored water", an
| indication of the probable presence of a seamount. The Navy
| determined that information regarding the seamount should
| have been transferred to the charts in use--particularly
| given the relatively uncharted nature of the ocean area that
| was being transited--and that the failure to do so
| represented a breach of proper procedures.
|
| Nonetheless, a subsequent study by UMass Amherst indicated
| that the Navy's charts did not contain the latest data
| relevant to the crash site because the geographical area was
| not a priority for the Defense Mapping Agency"
|
| source:
| https://en.wikipedia.org/wiki/USS_San_Francisco_(SSN-711)
|
| So it looks like the USN charts are not exactly cheap to
| generate. And there is a large human element of knowing where
| the charts are mostly accurate and where there is information
| missing.
|
| Also keep in mind both of these are attack submarines and not
| Ohio class which generally are routinely patrolling the sea
| very deep and remaining as operationally quiet as possible to
| act as nuclear deterrents.
|
| I think their track record is more interesting because they
| have to patrol and be extremely quiet (zero sonar).
|
| The SSN/fast attack subs usually are escorting other groups /
| actively following targets so they end up in situations they
| can't entirely control.
| randombits0 wrote:
| The reason current mapping data is difficult to
| find/distribute is because it is secret.
| nradov wrote:
| 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/
| dylan604 wrote:
| 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.
| 123pie123 wrote:
| not sure if ths is a daft question or not,
|
| but could they just reduce the power of the sonar?
| CapitalistCartr wrote:
| If you can pick it up, so can they.
| dylan604 wrote:
| 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.
| nabla9 wrote:
| 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.
| toomuchtodo wrote:
| https://seabed2030.org/
| somishere wrote:
| This is great, thanks for sharing.
| bitsandbooks wrote:
| Because it gets a lot more expensive the deeper you want to
| go/look.
| hoyd wrote:
| "Everything about the seafloor is bigger, bolder, and more
| extreme than the comparatively quiet terrain we know as land."
|
| Well said :-)
| abulman wrote:
| > "The Ocean," it says, "is big. Really big. You just won't
| believe how vastly, hugely, mindbogglingly big it is. I mean, you
| may think it's a long way down the road to the chemist, but
| that's just peanuts to the ocean."
| candyman wrote:
| Check out Kraken Robotics. https://krakenrobotics.com/
| nabla9 wrote:
| If you have 100 ocean survey ships scanning the ocean floor 24/7
| moving 6 knots with 1 km wide side scan sonar, it takes over 900
| years to map all oceans.
| bradrn wrote:
| 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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(page generated 2023-11-11 23:00 UTC)