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Ping Jockey -> [Logged] Recommended Changes to the Sonar Model (3/6/2021 11:41:01 PM)
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I’m a former US Navy Sonar Technician who bought CMANO the first week it was released and have been enjoying it and CMO ever since. Great job overall – BZ to the entire development team. [&o]
Early on I noticed a couple of fundamental problems with the modeling/rules associated with sonar detection; specifically layer modeling and convergence zones (CZs). Sorry it’s taken me so long to propose corrections (truth to tell, I was hoping someone else would do it <g> ).
I understand that the current sonar model in CMANO / CMO does not include environmental factors such as weather, sea state (as it relates to mixing in the near-surface layer) or – most importantly - seasonal variations. This is unfortunate, but I realize that implementation of these factors would be very difficult – more so than modeling worldwide terrain, since mountains do not move and change height on a seasonal basis. Consequently, I restrict my recommendations to modifications to the existing static environmental models.
Layer Strength
The difference between the temperature of the near-surface mixed layer and the ocean deeps determines the strength of the acoustic layer. The greater the difference, the stronger the layer. The ocean deeps keep a fairly constant temperature of ~39° F (~4° C), thus a warmer mixed near-surface layer gives a stronger acoustic layer effect.
Command elegantly models this by indexing the layer strength to latitude on the map. The strongest layer (0.7) is at the equator, and every 18° change in latitude reduces the layer strength by 0.1 until it gets to 0.2 at the North Pole (in CMANO, it was 0.01 per 1.8° (1° 48’)).
Note: The model actually uses an 18° band at the equator that is split between the northern & southern hemispheres and thus is 9° on each side of the line. Similarly, the radius of the 0.2 layer strength at the pole is 9° to give it a diameter of 18°. Thus the current layer strength bands are:
81°N – 0.2
63° N – 0.3
45° N – 0.4
27° N – 0.5
9° N – 0.6
0° 00’ – 0.7
9° S – 0.6
27° S – 0.5
45° S – 0.4
63° N – 0.3
… to Antarctica
The Problem
Although near-surface mixed layers exist in polar waters (where there isn’t pack ice) above 60° - 70° latitude, the temperature of these layers is usually close to - or even colder than – the deep water. Without the warm-over-cold thermocline, you don’t get the shadow zones “below the layer” in which a submarine can hide. To put it simply, the acoustic layer doesn’t exist in far northern or southern waters.
Why it’s Important
The Soviet Union put a lot of effort into building large ASW ships – Kresta-II, Kara, Udaloy and even Kiev classes; at first to attack US Polaris missile-launching SSBNs, then later to defend Soviet SSBN bastions when improved SLBM ranges moved enemy SSBN away from – and allowed Soviet SSBNs to patrol closer to – Soviet home waters in the Barents Sea.
Although surface ships are usually at a strong acoustic disadvantage against submarines, the layer-free “terrain” of northern waters helps to mitigate this, and the Soviets/Russians built their ships and tactical doctrine accordingly. This affects ASW scenarios in what would likely be a hotly-contested area in a general war.
How to Fix It
North of the equator, change the latitude increment in which the layer strength changes by 0.1 from 18° to 10°.
South of the equator, change the latitude increment in which the layer strength changes by 0.1 from 18° to 9°.
70° N – 0.0
60° N – 0.1
50° N – 0.2
40° N – 0.3
30° N – 0.4
20° N – 0.5
10° N – 0.6
0° 00’ – 0.7
9° S – 0.6
18° S – 0.5
27° S – 0.4
36° S – 0.3
45° S – 0.2
54° S – 0.1
63° S – 0.0
Convergence Zones
Section 9.2.3 (page 238) of the CMO manual (and 8.7 (page 134) of the CMANO manual) states,
"CZ detections are possible only if the local depth provides at least 600ft/200m clearance under the target."
and
"CZ intervals range from 40nm in the poles to 20nm in the equator, depending also on local temperature."
The bad news is that both statements are almost completely wrong.
The good news is that both should be easily fixable (based on my understanding of Command’s sonar model – I can hear the programmers’ eyes rolling from where I sit). When correctly modeled, the statements should read,
"CZ detections are possible only if the water depth is at least 1700 – 4600m (5600 – 15100ft), depending on local water temperature near the surface. This is modeled as a function of the sensor’s latitude above or below the equator."
and
"CZ intervals range from 20nm near the Arctic/Antarctic circle to 40nm at the equator, depending again on local water temperature. CZs are not available from 70-degrees latitude to the poles."
Correcting the CZ parameters is slightly more complicated ([8|]) than correcting the layer because in addition to correcting the CZ ranges, we are changing the minimum water depth figure for CZ availability from a constant to a variable (note that the actual minimum depth is MUCH deeper than is currently modeled). Also, since the presence of Convergence Zones depends on the presence of a surface layer (in which the negative sound gradient focuses – i.e. “converges” the sound), if there is no Layer (or it is very weak), there is no CZ. As above, there can be no Convergence Zones in Arctic or Antarctic waters.
Currently (as with Layer Depth), CZ ranges are indexed to latitude on the map. The longest range to the first CZ (40nm) is close to the North Pole (above 87° 45’N), and every 4.5° (4° 30’) change in latitude reduces the first CZ range by 1nm until it gets to 20nm near the Equator (2° 15’N to 2° 15’S).
To more accurately model Convergence Zone ranges and availability, set the maximum CZ range (40nm) at the Equator. Set the minimum depth for CZs at the Equator to 5380m. North of the Equator, the latitude interval should be 3.4° (3° 24’) and south of the Equator it should be 2.9° (2° 54’).
For each interval north or south of the Equator, reduce the CZ range by 1nm and the minimum depth allowable by 220m.
Latitude 1stCZ 2ndCZ 3rdCZ 4thCZ Min Depth (m)
69° 42’ No CZ No CZ No CZ No CZ ---- n/a
66° 18’---20-----40-----60-----80------980
62° 54’---21-----42-----63-----84-----1200
59° 30’---22-----44-----66-----88-----1420
56° 06’---23-----46-----69-----92-----1640
*
*
*
8° 30’----37-----74----111----148-----4720
5° 06’----38-----76----114----152-----4940
1° 42’----39-----78----117----156-----5160
0° 00’----40-----80----120----160-----5380
1° 27’----39-----78----117----156-----5160
4° 21’----38-----76----114----152-----4940
7° 15’----37-----74----111----148-----4720
*
*
*
47° 51’---23-----46-----69-----92-----1640
50° 45’---22-----44-----66-----88-----1420
53° 39’---21-----42-----63-----84-----1200
56° 33’---20-----40-----60-----80------980
59° 27’ No CZ No CZ No CZ No CZ ---- n/a
Like the rest of the sonar model, this is a linear simplification of a curved function, but it is 95% accurate to within 100m of typical depth minimums.
Thank you for your hard work continued dedication to making this the best modern war sim ever.
References:
Urick, Robert J. “Principles of Underwater Sound” 3rd Edition Peninsula Publishing 1983
Urick, R. J. “Sound Propagation in the Sea” DARPA U.S. Government Printing Office 1979
Cle´ment de Boyer Monte´gut, Gurvan Madec, Albert S. Fischer, Alban Lazar,
and Daniele Iudicone, “Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology” Published in the Journal of Geophysical Research, Vol. 109, 2004
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