[FIXED] Sonar range (Full Version)

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pclaurent -> [FIXED] Sonar range (5/17/2020 8:16:46 AM)

I am surprised by the range of sonars in CMO. It often seems very exaggerated to me. For example: I am aboard an SSN in static diving at 59 m depth. A Borey II class SSBN is approaching from the west at a speed of 5 knots, also at 59 m depth (the layer is at 69 m, the ocean floor at 4800 m). This way, the Borei is perceived by my sonar at a distance of 6.7 nautical miles.

As far as I know, the Borey is one of the quietest SSBNs (95 dB). This type of submarine should never be detected more than a few thousand meters (it even happens that they are not detected at 100 m, which explains some collisions between submarines). In addition the ocean depth (4800 m) excludes a bottom bounce, and the short contact distance does not involve a convergence zone.

Dangerous Waters seems more realistic about the sonar range. In this game it is practically impossible to detect another submarine more than 5000 or 6000 meters away.

I found an interesting source on the subject of the ability to detect submarines by passive sonar: https://fas.org/spp/eprint/snf03222.htm

Could you tell me if it could be an inaccuracy in CMO, or if this reflects some physics unknown to me?



Dimitris -> RE: Sonar range (5/17/2020 8:21:12 AM)

Can you post a save of the example you are describing?

From your description, I suspect that the subs are close enough to the surface that some amount of ducting is taking place, amplifying the sound transmission.

(FWIW, others have in the past repeatedly dogged us because we supposedly have "too low" sonar detection ranges. I distinctly remember one guy giving us hell because he could not, in the Falklands area, perform multi-CZ detections as described by Clancy in the Barents Sea. When I explained to him the differences in environment he mysteriously disappeared. I think many people come to CMO with a lot of pre-conceptions, right or wrong, and when these are not perfectly replicated in CMO they suspect the sim itself, instead of the validity of their pre-conceptions. Just a thought!)



pclaurent -> RE: Sonar range (5/17/2020 8:39:19 AM)

No doubt there are good reasons for all that - just trying to understand.
I attached the save file.



Dimitris -> RE: Sonar range (5/17/2020 10:48:34 AM)

Okay, I found it. The sonar code is fine, but there was an error in the AI evasion logic.

Basically the Borei detected the Rubis first (small wonder), and correctly engaged a careful slow-evasion logic, ie. place the threat at her six and creep away. The problem was that the logic included two contradictory commands: Set desired shaft-speed to slow (reasonable), and set the throttle to flank (WTF!!!!!). This spiked the powerplant noise and allowed the Rubis to detect her.

Fixed it now, and the Borei will correctly creep away from the detected threat like a whisper.

Thanks for the heads up, and especially for the prompt save file! Without it it would have been impossible to dig this out.



pclaurent -> RE: Sonar range (5/17/2020 8:38:40 PM)

Thanks Dimitris. I'll continue checking sonar ranges somehow (I'm reading some litterature about sonar equations, even if I'm not very comfortable with all this maths stuff). At this point, I think that a maximum range of about 5000 m in deep waters for detecting an SSBN or a modern SSN is reasonable (tell me if I'm wrong).



Dimitris -> RE: Sonar range (5/17/2020 8:42:01 PM)

There are a ton of factors involved so any "hard" figure is likely to be very situation-dependent.

As a temporary workaround until the next update release, you can disable the "auto evasion" doctrine option for the Borei. This will disable the "slow evade" logic and thus avoid this issue.



pclaurent -> RE: Sonar range (5/17/2020 9:05:08 PM)

Retried the scenario with a static Rubis. Borei coming from west is now detected first while continuing its way to the east.

Try running the attached scenario and fast forward until Borei is about 6.7 nm from Rubis.



Dimitris -> RE: Sonar range (5/17/2020 9:12:15 PM)

Yes, this is consistent with a test that I ran before discovering the AI bug:

The "DMUX 20 [DSUV 2H + DUUA 2D]" hull sonar is attempting to detect the Borei at 8.36nm .

* The sonar has a nominal range of 40nm (best performance against reference-maximum target going flat-out)
* The "own noise" modifier is 1 (the own submarine is dead in the water).
* Target target noise modifiers are 0.299 for the powerplant & propeller (creep shaft speed) and 0.132 for flow noise (vessel is creeping). This results to an overall target noise modifier of 0.257.
* The acoustic band is LF, at this band the reference-maximum is 112db. Target signature (rear) is 67db, so the target noise ratio is 0.59.
* The combination of the nominal range, the own-noise modifier, the target-noise modifier and the target noise ratio results in a practical detection range of 6.16nm.
* No effect of surface duct, thermal layer or DSC. Also no effect from reverberations.

So in this example the detection check was unsuccessful, but the feasible detection range was pretty close to what you mentioned.



pclaurent -> RE: Sonar range (5/17/2020 9:19:41 PM)

OK, I'm just still wondering if such an SSBN is so easily detectable by an ordinary SSN...



pclaurent -> RE: Sonar range (5/17/2020 9:42:31 PM)

Here is my reasoning:
At 6.7 nm, the perceived noise of the Borei should be roughly: 95-20*Log(6.7*1852) = 13 dB
(and this simple spherical diffusion formula does not account various attenuation factors).
I doubt that any sonar can detect such a whisper that is far below sea noise (around 60 dB in a very calm sea, wind 0).



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