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Comment by jmacd | Hacker News Reader

My boat has a $1000 piece of garmin equipment which will tell me exactly how far away the landmass under me is, and has another sonar angled forward which tells me a little bit about what's coming up.

It's possible that this type of sensing equipment isn't used when they are in hostile environments?

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Do you really not see what the issue may be with constantly broadcasting a sonar signal would be from a military submarine?

See my other posts - they should not have had to have had sonar on to detect the seamount. My question, is why did the two other alternatives not work (i.e.: inertial navigation and gravity detection)?

What do you keep talking about on this thread regarding gravity detection? Please link to a device that does that. Google only brings up gravity wave detectors.

How is inertial navigation supposed to work for an unmapped seamount? Sure that works for known seamounts but how’s that going to help around things that move due to tectonic plates or undersea volcanos? Or in unmapped or mis-mapped regions?

I cannot believe there's any argument about this. There are literally thousands of references. Below, are links to the first few references that I found.

Note: you'll see that in the first link in item #5 the comment about the strategic nature of this information, that means don't expect to get how-to-do-it plans from the military but you can bet your house to a brick that the military is deeply involved in gravity detection (specifically because, like inertial navigation, it's silent and doesn't broadcast its presence).

Also note the dates, this stuff goes back to even before the 1970s, the technology is now very mature.

"Google only brings up gravity wave detectors."

See Google's patent in item #5.

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Links as requested:

1. General Information/Overview

https://en.wikipedia.org/wiki/Gravity_anomaly

https://en.wikipedia.org/wiki/Gravity_gradiometry

https://csegrecorder.com/articles/view/magnetic-and-gravity-...

https://www.911metallurgist.com/blog/wp-content/uploads/2015...

http://www.ga.gov.au/pdf/RR0027.pdf

2. Commercial

https://www.geologyforinvestors.com/gravity-surveys/

3. Underwater

https://www.whoi.edu/cms/files/08oceans-1_41284.pdf

https://www.sciencedirect.com/science/article/abs/pii/S00298...

https://library.seg.org/doi/10.1190/geo2018-0090.1

4. Military specific

https://www.navysbir.com/n09_1/N091-092.htm [Note the comment re the strategic nature of this information.]

https://apps.dtic.mil/dtic/tr/fulltext/u2/1012150.pdf

https://slate.com/culture/2013/10/the-hunt-for-red-october-m...

5. Even Google has a patent!

https://patents.google.com/patent/US5339684A/en

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Edit: Just found this very specific reference too, but it's not free: https://pubs.geoscienceworld.org/tle/article-abstract/34/12/...

Thankyou, that was a very list.

You're most welcome. :-)

The Garmin device they’re talking about is active sonar. That means it makes a big noise. It’s like shining a light into a dark room - everyone can see where the light is coming from.

Your boat is not trying to evade enemies that may want to locate and destroy it, so it doesn't matter if it is constantly emitting sound.

In submarines active sonar is rarely if ever used. It will give you away instantly to anyone around you and then you give enemies your unique sonar signature. China and Russia could easily say Seawolf XXX is the South China Sea right now pinging around. This is SIGINT 101.

Submarines have the same radar and sonar we use for fishing when they are navigating public waterways and inlets. They do not use the military grade stuff in those situations.

The entire point of a submarine is that nobody knows it's there. If they are using easily detectable equipment then people who are listening know they are there.

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