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Radar does not penetrate through brine water. Other remote sensing techniques have such poor resolution that they are relatively useless for this task. Unfortun

Radar does not penetrate through brine water. Other remote sensing techniques have such poor resolution that they are relatively useless for this task. Unfortunately, sonar based bathymetry is really the best tool for this task and that means you have to run around with a surface ship mapping out the sea. As you can imagine the Chinese are not a big fan of American ships doing that in waters that they claim to be theirs.

wolverine876 5y ago
> sonar based bathymetry is really the best tool for this task and that means you have to run around with a surface ship Why can't it be done from a plane or satellite? I can imagine answers (e.g., sound doesn't travel as well through air), but does anyone know? > the Chinese are not a big fan of American ships doing that in waters that they claim to be theirs I'd be surprised if that stopped the US in this circumstance. They regularly conduct operations in the South China Sea.
- simonh 5y ago
  The kind of sensors you can put on a plane or satellite simply can’t penetrate seawater effectively. It absorbs radar, dissipates heat and light. Sonar sound waves in air mostly just bounce off the ocean surface. This is why submarines are so stealthy and therefore militarily useful. As long as they stay quiet they’re almost impossible to detect without using relatively short range active sonar.
- roywiggins 5y ago
  Sound doesn't transmit well at all between air and water in either direction. It just bounces off. You can't hear what's going on underwater when you're out of the water and you can't hear what's going on above water when you're underwater.
  - nitrogen 5y ago
    How do anti-glare coatings on lenses work? Could something similar be devised for the air-water interface?
    - stickfigure 5y ago
      Sure. You just need to apply your anti-glare coating to the world's oceans.
      - nitrogen 5y ago
        I mean for acoustic waves. Alternatively/similarly, could an aerial sonar waveform be matched to the ocean surface waves to cause constructive interference below the surface, and destructive above it? Would it be possible to recover the reflections afterward? https://en.wikipedia.org/wiki/Anti-reflective_coating https://en.wikipedia.org/wiki/Anti-reflective_coating > Layer thicknesses are chosen to produce destructive interference in the beams reflected from the interfaces, and constructive interference in the corresponding transmitted beams. This makes the structure's performance change with wavelength and incident angle, so that color effects often appear at oblique angles.
- zitterbewegung 5y ago
  Water isn’t air? Even air can become opaque.
- woeirua 5y ago
  Sound doesn't travel as well through the air, but it still does. The primary reason that you can't do it from the air is that the surface of the ocean is a big irregular reflector of acoustic energy from the air, so the overwhelming majority of the energy will be lost. It just would never be practical. It might be possible to use airborne gravity gradiometry to map seaborne mounts. I'd never considered that before, but I see no reason to think it wouldn't work.
  - TheOtherHobbes 5y ago
    I'm finding it hard to believe that satellite and/or local gravimetry would entirely miss an underwater mountain.
- nradov 5y ago
  The air / water interface makes it impossible to get any useful sonar data from an aircraft. Some military helicopters carry dipping sonar that they can temporarily lower into the water, and specialized aircraft can also drop sonar buoys, but those are designed for detecting submarines and are mostly useless for bathymetry. The US Navy does regularly operate in the South China Sea. In fact the USNS Mary Spears oceanography research vessel was there recently, presumably gathering bathymetry and other data. https://www.marinevesseltraffic.com/vessels/USNS-Mary-Sears-(T-AGS-65)/CURRENT-POSITION/9207077/303859000 https://www.marinevesseltraffic.com/vessels/USNS-Mary-Sears-...
  - wolverine876 5y ago
    Thanks. (I'd upvote you but for some reason votes don't stick, on comments and stories: When I reload the page, the arrows return, as if I hadn't voted. flag/vouch behaves normally. Perhaps a mod will read this.)
    - dredmorbius 5y ago
      Votes typically take a few seconds to resolve, possibly longer under load. HN's JS indicates them immediately when you're on the page. Check your profile's upvoted comments / posts link (https://news.ycombinator.com/upvoted?id=wolverine876&comments=t https://news.ycombinator.com/upvoted?id=wolverine876&comment... -- that's private for you only) to see if your upvotes have been registered. If not, drop a line to hn@ycombinator.com as I suspect they'll be interested.
      - wolverine876 5y ago
        Thank you. No upvotes in 2 days via that link and I'm not that stingy! I upvoted your comment just before I wrote this.
        dredmorbius 5y ago
        I'm confirming either no upvotes (or at least balanced ones) on my GP comment above.
stickfigure 5y ago
> As you can imagine the Chinese are not a big fan of American ships doing that in waters that they claim to be theirs. Why does anyone (besides China) care? Nobody in that region recognizes those claims.
- wolverine876 5y ago
  > Why does anyone (besides China) care? Nobody in that region recognizes those claims. China has power, military and economic, and thus can't be ignored. If Fiji claimed a region of the Pacific, it wouldn't matter (in this respect).
  - tablespoon 5y ago
    >> Why does anyone (besides China) care? Nobody in that region recognizes those claims. > China has power, military and economic, and thus can't be ignored. If Fiji claimed a region of the Pacific, it wouldn't matter (in this respect). It isn't ignored, but that doesn't mean those claims are recognized. The US (at least) takes actions to specifically show that: https://en.wikipedia.org/wiki/Freedom_of_navigation#Freedom_of_Navigation_Operations_(FONOPs) https://en.wikipedia.org/wiki/Freedom_of_navigation#Freedom_...
    - wolverine876 5y ago
      > It isn't ignored, but that doesn't mean those claims are recognized. Agreed. The GGP was asking if anyone cared. People certainly care about the claims, even if they don't recognize them.
- toyg 5y ago
  Because China happens to have nukes, probably.
ASlave2Gravity 5y ago
A good techno-thriller might be some group of hackers nab the Chinese bathymetry database, which then finds its hands in some war hungry US general

wolverine876 5y ago

> sonar based bathymetry is really the best tool for this task and that means you have to run around with a surface ship Why can't it be done from a plane or satellite? I can imagine answers (e.g., sound doesn't travel as well through air), but does anyone know? > the Chinese are not a big fan of American ships doing that in waters that they claim to be theirs I'd be surprised if that stopped the US in this circumstance. They regularly conduct operations in the South China Sea.

simonh 5y ago
The kind of sensors you can put on a plane or satellite simply can’t penetrate seawater effectively. It absorbs radar, dissipates heat and light. Sonar sound waves in air mostly just bounce off the ocean surface. This is why submarines are so stealthy and therefore militarily useful. As long as they stay quiet they’re almost impossible to detect without using relatively short range active sonar.
roywiggins 5y ago
Sound doesn't transmit well at all between air and water in either direction. It just bounces off. You can't hear what's going on underwater when you're out of the water and you can't hear what's going on above water when you're underwater.
- nitrogen 5y ago
  How do anti-glare coatings on lenses work? Could something similar be devised for the air-water interface?
  - stickfigure 5y ago
    Sure. You just need to apply your anti-glare coating to the world's oceans.
    - nitrogen 5y ago
      I mean for acoustic waves. Alternatively/similarly, could an aerial sonar waveform be matched to the ocean surface waves to cause constructive interference below the surface, and destructive above it? Would it be possible to recover the reflections afterward? https://en.wikipedia.org/wiki/Anti-reflective_coating https://en.wikipedia.org/wiki/Anti-reflective_coating > Layer thicknesses are chosen to produce destructive interference in the beams reflected from the interfaces, and constructive interference in the corresponding transmitted beams. This makes the structure's performance change with wavelength and incident angle, so that color effects often appear at oblique angles.
zitterbewegung 5y ago
Water isn’t air? Even air can become opaque.
woeirua 5y ago
Sound doesn't travel as well through the air, but it still does. The primary reason that you can't do it from the air is that the surface of the ocean is a big irregular reflector of acoustic energy from the air, so the overwhelming majority of the energy will be lost. It just would never be practical. It might be possible to use airborne gravity gradiometry to map seaborne mounts. I'd never considered that before, but I see no reason to think it wouldn't work.
- TheOtherHobbes 5y ago
  I'm finding it hard to believe that satellite and/or local gravimetry would entirely miss an underwater mountain.
nradov 5y ago
The air / water interface makes it impossible to get any useful sonar data from an aircraft. Some military helicopters carry dipping sonar that they can temporarily lower into the water, and specialized aircraft can also drop sonar buoys, but those are designed for detecting submarines and are mostly useless for bathymetry. The US Navy does regularly operate in the South China Sea. In fact the USNS Mary Spears oceanography research vessel was there recently, presumably gathering bathymetry and other data. https://www.marinevesseltraffic.com/vessels/USNS-Mary-Sears-(T-AGS-65)/CURRENT-POSITION/9207077/303859000 https://www.marinevesseltraffic.com/vessels/USNS-Mary-Sears-...
- wolverine876 5y ago
  Thanks. (I'd upvote you but for some reason votes don't stick, on comments and stories: When I reload the page, the arrows return, as if I hadn't voted. flag/vouch behaves normally. Perhaps a mod will read this.)
  - dredmorbius 5y ago
    Votes typically take a few seconds to resolve, possibly longer under load. HN's JS indicates them immediately when you're on the page. Check your profile's upvoted comments / posts link (https://news.ycombinator.com/upvoted?id=wolverine876&comments=t https://news.ycombinator.com/upvoted?id=wolverine876&comment... -- that's private for you only) to see if your upvotes have been registered. If not, drop a line to hn@ycombinator.com as I suspect they'll be interested.
    - wolverine876 5y ago
      Thank you. No upvotes in 2 days via that link and I'm not that stingy! I upvoted your comment just before I wrote this.
      - dredmorbius 5y ago
        I'm confirming either no upvotes (or at least balanced ones) on my GP comment above.

stickfigure 5y ago

> As you can imagine the Chinese are not a big fan of American ships doing that in waters that they claim to be theirs. Why does anyone (besides China) care? Nobody in that region recognizes those claims.

wolverine876 5y ago
> Why does anyone (besides China) care? Nobody in that region recognizes those claims. China has power, military and economic, and thus can't be ignored. If Fiji claimed a region of the Pacific, it wouldn't matter (in this respect).
- tablespoon 5y ago
  >> Why does anyone (besides China) care? Nobody in that region recognizes those claims. > China has power, military and economic, and thus can't be ignored. If Fiji claimed a region of the Pacific, it wouldn't matter (in this respect). It isn't ignored, but that doesn't mean those claims are recognized. The US (at least) takes actions to specifically show that: https://en.wikipedia.org/wiki/Freedom_of_navigation#Freedom_of_Navigation_Operations_(FONOPs) https://en.wikipedia.org/wiki/Freedom_of_navigation#Freedom_...
  - wolverine876 5y ago
    > It isn't ignored, but that doesn't mean those claims are recognized. Agreed. The GGP was asking if anyone cared. People certainly care about the claims, even if they don't recognize them.
toyg 5y ago
Because China happens to have nukes, probably.

ASlave2Gravity 5y ago

A good techno-thriller might be some group of hackers nab the Chinese bathymetry database, which then finds its hands in some war hungry US general