Do I understand this sonar SSP stuff correctly?

[MarkShot]

I have read various documents on using the SSP information in the sub's sonar station.

I was just reading over Notfallmappe v6. It states that if two equivalent subs are listening for each other (assuming no layer) that the one located where sound travels fastest (fastest SSP) will have the best chance of detecting the other.

From my readings, I have come to understand that the opposite would be true. Due to the fact that sound waves are bent towards the slower SSP.

As I understand it:

(1) Sound waves are bent towards the slower SSP.

(2) Because of this bending behavior sound tends to travel into slower SSP water from faster SSP water and sound tends to not travel into faster SSP water from slower SSP water.

(3) Thus, if there is no layer or two subs are on the same side of a layer, then the sub in the slower SSP water has the better chance to detect the sub in the faster SSP water at some appropriate distance. (assuming equivalent subs)

(4) If there is a layer such that the water below the layer has the slowest SSP compared to water above the layer, then it is possible for a sub below the layer to hear sounds generated above the layer, but for sonar above the layer to be unable to hear sounds generated below the layer.

(5) If the layer itself should manifest the slowest SSP, then sounds which travel into the layer could be conveyed over an extended distance.

(6) If the layer itself should have the highest SSP, then this leads to a shadow zone where a hiding sub cannot be heard.

(7) Sound refracts in water in accordance to the SSP. Sound also reflects off the surface and the bottom. (This reflection is impacted by sea state and bottom type.)

---

My question is do I understand this stuff right? (every time I read something new I begin to wonder)

Thanks.

[MarkShot]

PING!

Where are all you experts and Navy veterans?

[Bellman]

Anyone not on holiday is lazing in the garden with ice cold drinks.
Taken me a week to get the message. (See Poll limits etc.)

Fish posted some excellent stuff from Blackjack of the Seawolves on the topics you raise. Sure a search will turn it up .


Its 'Life gets tedious' time.

[MarkShot]

The thing is that I have read those materials and other such materials. However, I am trying to see if I reached a simple and correct understanding. Hopefully, to be confirmed by someone with a deep and thourough understanding.

Thanks.

[Bellman]

Good hunting - thats the 'Holy Grail' a ''simple'' understanding - I am still searching for the like -
on TMA, Scenario Design triggers etc.

My rather unsubtle point was that probably people just cant be bothered to muster the energy
and concentration to reply at this moment of time.

We shall see .

Cheers.

[timmyg00]

Patience, friends...

I will try to answer the SSP questions tonight after work.

You guys are as bad as my customers... "I want an answer YESTERDAY!!"



TG

[MarkShot]

There is just so much confusing and contradictory information out there.

For example, I have some of Blackjack materials printed out that explains how a layer need not be isometric and not act as a sound mirror - meaning that sound may propagate across the layer more easily from one side than the other.

However, I was reading Notfallmappe v6 today and in explaining the principles of ASW it notes that the layer is like a mirror trapping sound from crossing it either way.

So, my problem isn't so much lack of willingness or effort applied to understanding sonar passive/active concepts. Instead it is more like it is impossible to find a definitive and comprehensible source. A source from which a lay person could derive some basic and sound principles to be used as rules of thumb in game play.

Finally, of course, there is the issue of how sound propagation/detection is modeled in DW and SC (that's what I am playing) which may not necessarily reflect realworld behavior.

Yep, so, there is the SSP button with a nice little graph. I know it should be an aid to me, but either I don't know how to use this information or I lack confidence in what I think know.

---

Compared to WWII subsims the layer stuff was trivial. In SHI, you get below the layer and you are fairly safe and invisible at low speeds. Even without the bathythermograph, the resonance of pings changes dramatically as you pass through a layer. In SH2, you get this little announcement by sonar as you pass through. It diminishes the ease at which you are located, but not nearly as absolute as SH1.

Then you have SC and DW. I have had SC since it was originally released. I may be playing it five years from now and still be mystified by the "layer".

---

Timmyg00,

Perhaps now, that you are reknown for your "TMA for dummies/lay people/gamers"; it is time to move on to greater fame with "Active/Passive Sonar: Layers, SSP, seastates, bottom types and applying it effectively in SC/DW".

Thanks.

[MarkShot]

Oops! My mistake ... that was TopTorp who did the TMA thing. You wrote the SCHQ Tacman.

In any case ... all help is much appreciated.

[Dr.Sid]

This is how it works in real life. In DW the sound model is simpler. It is not exactly known how much simpler. There are some layer effects, but quite weak. I played many test missions and was helped by others just to find there is any SSP effect at all. Just do some test, you'll see.
What I found: You get weaker signal if you are on oposite side of the layer. The loss of the signal strength is 10% to 50%. Very occasionaly you can loose narowband line, in some very specific distance I think it is possible to loose contact, but it never happened to me. Most often layer does NOT change your ability to track or even identify.
Surface noise has much stronger effects. Shallow listener is affected by it and his contacts will be masked by surface noise. The noise reaches depths about 50m with sea state=3 and your detection range is several times smaller. You can completely loose contact which you have identified with 4 lines just few feet deeper. This is also main reason why deep sonobuoy has bigger range.
Surface noise effect is gradully stronger towards the surface. On waterfall display you can see lines gradually 'sink' in the noise while getting shalow. Layer effects in DW give sharp intensity change, and they occur EXACTLY on the layer depth.
While testing, note that towed array is usually in different depth then ship. If possible, use Sphere array to test SSP effects. Also note that on american subs narowband display you can see line fading away if the target changes bearing. Target gradualy moves to next bearing 'beam'.
This can be mistaken as SSP effect is bearing change is slow.

[MarkShot]

I was playing SCXIIc yesterday and engaging a Kilo with an Akula.

I had a very faint contact just good enough do TMA and DEMON. When it sped up (because I was shooting at it), I could easily track it above the layer. However, when it slowed to 3KTS, I would lose it on DEMON until I dove below the layer. I had that happen a few times.

[Bellman]

Taking up Dr. Sid's point I think near bottom turbulence, not TA related, is modeled well over certain surfaces.
Could be a passive torp beater in SC , but by no means infallible.

Also have witnessed the fading in and out of tonals in long distance duct 'boosting'. But cannot be sure
whether this is accurately modeled or just a feature of the variable (shades) receptivity, or water conditions, factored into the sim.

[timmyg00]

A couple of excerpts from the TACMAN:

MISCONCEPTION: Thermal layers will always hide you from an enemy that is
on the other side of the layer.
TRUTH: The thermal layer is not the “glass ceiling� or “magic shield� that many
players believe it to be.
This misconception springs primarily from the behavior of early PC
submarine simulation games, in which the acoustic environment was not as
accurately modeled as it is in Sub Command. Thermal layers in early sims
seemed to behave as a “glass ceiling�; signal strengths would drop significantly
as the thermal layer was crossed. This caused many players to believe that this
behavior is normal.

definitions:
· isothermal: little or no temperature change with increasing depth; leads to little
or no sound-speed change with depth
· positive gradient: speed of sound increases with depth
· negative gradient: speed of sound decreases with depth
· boundary: the depth at which two gradients meet, also known as the thermal
layer, boundary layer, sonic layer

From what I had read in FAS - used as a reference source for the TACMAN - wavefronts are refracted UP toward the shallows in a positive gradient, and DOWN toward the depths in a negative gradient. This indicates (and was reported by FAS) that the wavefronts are refracted towards water with a slower sound speed.

As to the original questions in this post:

Originally Posted by MarkShot

(1) Sound waves are bent towards the slower SSP.

Correct.

Originally Posted by MarkShot

(2) Because of this bending behavior sound tends to travel into slower SSP water from faster SSP water and sound tends to not travel into faster SSP water from slower SSP water.

Also correct.

Originally Posted by MarkShot

(3) Thus, if there is no layer or two subs are on the same side of a layer, then the sub in the slower SSP water has the better chance to detect the sub in the faster SSP water at some appropriate distance. (assuming equivalent subs)

Correct, although this should be qualified by citing the surface noise mentioned above; in a positive gradient, the sound waves are refracted up toward the shallows, where surface noise is greater. This indicates to me that there would be less benefit in lingering near the surface in a positive gradient environment in an effort to gain contact on a quiet submarine. On the other hand, in a negative gradient environment, there would be more benefit in going deeper to take advantage of the downward refraction.

Originally Posted by MarkShot

(4) If there is a layer such that the water below the layer has the slowest SSP compared to water above the layer, then it is possible for a sub below the layer to hear sounds generated above the layer, but for sonar above the layer to be unable to hear sounds generated below the layer.

This one is tricky. The environment in question would have a negative gradient on BOTH sides of the layer, with one gradient being sharper than the other (probably the one on the top). Not impossible, but I don't recall ever seeing it in SC or DW (not that it never happens, but that I just don't remember seeing it ) However, if this environment existed, I'd say that this is largely correct - except that I'd replace "unable" with "less able".

Originally Posted by MarkShot

(5) If the layer itself should manifest the slowest SSP, then sounds which travel into the layer could be conveyed over an extended distance.

Correct. This is called a "sound channel", and is usually only seen at the boundary with the thermocline (not to be confused with thermal layer).

Originally Posted by MarkShot

(6) If the layer itself should have the highest SSP, then this leads to a shadow zone where a hiding sub cannot be heard.

Correct again; this is called a "surface duct" environment. However, in such a surface duct environment, one that produces a shadow zone where the wavefronts diverge, only very sharp gradients on either side of the layer will produce a shadow zone that acts like the "glass ceiling" mentioned above.

Originally Posted by MarkShot

(7) Sound refracts in water in accordance to the SSP. Sound also reflects off the surface and the bottom. (This reflection is impacted by sea state and bottom type.)

Correct. Rocky bottoms product the best reflections; reflection ("bounce") quality is less for a mud bottom, and worst for a sand bottom. As for surface conditions, I am guessing, but a calm surface should produce better reflections (as well as low noise), while a choppy or wavy surface produces scattered reflection and higher noise.

TG

[PeriscopeDepth]

Originally Posted by timmyg00

Correct. Rocky bottoms product the best reflections; reflection ("bounce") quality is less for a mud bottom, and worst for a sand bottom. As for surface conditions, I am guessing, but a calm surface should produce better reflections (as well as low noise), while a choppy or wavy surface produces scattered reflection and higher noise.

TG

Is this how it is real life concerning bottom reflection? It's always struck me as weird that mud is better at 'bouncing' sound than sand.

Thanks

[MarkShot]

TG,

Thanks very much for your time to review and comment. I shall now sail forth with much greater confidence. (If only the crew would stop their infernal wispering when I turn my back!)

[Bellman]

Nice little display Mark. Its called 'strutting your stuff '

Whens the write-up due ? If its half as good as your EAW stuff it will be a real treat. Looking forward to that.