Estimate submarine's depth

[MBot]

Considering how sound propagates in water and that sound waves that are received from the lower hemisphere might still originate from a source above you, shouldn't it be extremely hard to determine target depth?

[The Bandit]

Originally Posted by MBot

Considering how sound propagates in water and that sound waves that are received from the lower hemisphere might still originate from a source above you, shouldn't it be extremely hard to determine target depth?

Yes, as far as I know (unless maybe this was changed with some of the new stuff they have out now like WAA and whatever the bottom-bounce donut type deal that's mounted on the bottom of the Virginia class) determining exact depth has always been a problem.

I'd have to find it but one of the manuals for the Mk 37 torpedo basically says since you're probably not going to know your target's depth here's how to bracket with three staggered torpedoes, one shallow (60-300) , one medium (300-700) and one deep (700 and beyond).

My limited understanding of the matter though, when thermoclines are involved and the contact is localized, its usually enough to figure out "above or below the layer" and set the weapon for that approx depth (shallower or deeper than the layer) and let it do its work.

[SeaCadt07]

Estimating depth is just that. An estimate. But you can usually get a ballpark idea from context, such as acoustic conditions, weather, geography, Intel, time of day, mission, etc.

Unfortunately, no video game is going to be able to give you all the context you would have in real life to figure it out for yourself so the game just gives you the info.

[Destex]

The most sonar can do is provide an estimation whether the target is above or below the layer. Analyzing accurate depth is not possible.

[Aktungbby]

TYCZYW! A little required reading: https://fas.org/man/dod-101/navy/docs/fun/part09.htm In a nutshell:

Due to the fact that the principals of sound propagation through the water remain physical constants, in some respects ASW of the future will resemble that of World War II. There will be great differences, however, primarily attributed to the vast improvements in submarine and shipboard quieting technologies. Figure ( ) provides a historical perspective on the relative improvements in source levels of U.S. and Russian submarines. It is clear passive sensing of modern submarines is becoming difficult at best. With no control over target source levels and very little control over ambient noise, it becomes incumbent on systems designers and operators to maximize passive detection thresholds and directivity indices, along with continual implementation of self noise level improvements.

Continued emphasis will be placed on development of new sensor types and radical new concepts applied to current technologies. Some examples of innovation on the research and development forefront include:
- Fiber optic towed array: allowing higher data rates, and longer, lighter cables
- Satellite and aircraft based laser detection: Use of the electro-optic spectrum for ASW detection is receiving much attention. Implementation remains in the distant future, however. - Low frequency active towed arrays: With variable length and depth cables and longer range active sonar sources, the tactical disadvantage of active ASW revealing ownship position is reduced.

...and mind your 'Convergance Zone' at all times https://defence.pk/pdf/threads/tactics-101-anti-submarine-warfare-asw.270380/

[shipkiller1]

Originally Posted by jerseytom

If you're underwater in 3d space - target depth and bearing/distance I would think are fundamentally no different to measure - particularly with a spherical sensor array.

On US submarines, ALL bearings are 3D.

Originally Posted by PL_Harpoon

I think it all depends whether your sonar can get a 3d bearing or not.
If yes, then you don't even need to calculate it separately. Just do a simple trigonometry once you know your target's position.
If no, then things get a little bit more complicated.

Incorrect. You forget that sound in water does not travel in a straight line from the source. It bends based on the Sound Velocity Profile (SVP - Temp vs. Depth). It always follows the path of least resistance. This is how Convergence Zones (CZ) are created, for example.

Originally Posted by MBot

Considering how sound propagates in water and that sound waves that are received from the lower hemisphere might still originate from a source above you, shouldn't it be extremely hard to determine target depth?

Your terminology is incorrect. Not hemisphere, but depth. See above.

Originally Posted by Destex

The most sonar can do is provide an estimation whether the target is above or below the layer. Analyzing accurate depth is not possible.

In all actuality, the only way to determine if the noise source is above or below the layer (if there is one) is to see if the noise source has a higher Signal to Noise Ratio (SNR) when you are above the layer then below it. Own ship has to do a depth excursion.... You cannot determine the actual depth. Its really only 'is the contact above or below the layer'. If there is no layer, then you cannot determine what target depth is.

[shipkiller1]

To follow up and clarify this '3D'.

Submarine sonar systems determine not just the bearing (angle in the X axis) of the energy source but also the angle in the Y-axis. This is accomplished by Beam-forming.

You can read about it here in a unclassified PDF.

http://www.dtic.mil/dtic/tr/fulltext/u2/a250189.pdf

[Shadriss]

Originally Posted by shipkiller1

You forget that sound in water does not travel in a straight line from the source. It bends based on the Sound Velocity Profile (SVP - Temp vs. Depth). It always follows the path of least resistance. This is how Convergence Zones (CZ) are created, for example.

To further clarify and assist:

You are also making the assumption that the sound path is not having any interactions with the surface or bottom. Even if they don't, you have no way of knowing where along the path the actual origination point is, since range is always an estimate, no matter how good your solution is. But since, in most cases, all sound is going to have at least one surface/bottom interaction, it becomes impossible to determine depth at all.

There's even more factors involved, but that's the Cliff Notes version.