Sonar experts: How much sound crosses a layer?

[Molon Labe]

Have you tried 1.03 public beta yet? The SSP effects are MASSIVE. It seems like even very loud sounds cannot be heard across the layer.

Back in SC, when the layer effect was barely perceptible, it was a bit dissapointing but soon people explained to me how the SSP was supposed to work, and eventually I could use it a bit and see a small effect. I'm happy to see a stronger effect, but I'm in need of re-convincing that this is as it should be.

Are there any sonar experts that can comment on this? Thanks.

[Bill Nichols]

It really depends on how much the water temperature (sound speed) changes across the layer. I remember in the Med, during the summer, a very strong layer at about 100-150 feet. It was so strong that we often couldn't hear nearby surface ships until we came up to periscope depth. Had more than one 'Emergency Deep' as a result

[Molon Labe]

Originally Posted by Bill Nichols

It really depends on how much the water temperature (sound speed) changes across the layer. I remember in the Med, during the summer, a very strong layer at about 100-150 feet. It was so strong that we often couldn't hear nearby surface ships until we came up to periscope depth. Had more than one 'Emergency Deep' as a result

I'll have to play around and see if there are "strong" and "weak" layers in the game. Does the game choose the exact SSP profile at random within the specified SSP type, or does the exact shape of the SSP depend on things like depth and time of day or any of that sort of thing?

[sonar732]

"Strong" and "Weak" is determined by the "bend" of the SSP. The greater the bend...the stronger the layer. I've seen examples of SSP's where it "jacknifed" at the layer and it was really strong vrs. one that doesn't bend at all produces no layer basically.

[Driftwood]

It will be interesting to see how or if this "new" aspect of DW effects torp evasion tactics.

[SeaQueen]

Originally Posted by Molon Labe

I'm happy to see a stronger effect, but I'm in need of re-convincing that this is as it should be.

Are there any sonar experts that can comment on this? Thanks.

I haven't looked at the patch yet, but in addition to the temperature gradient, how effective the layer is should depend a lot on the frequency of the sound. Do you see the effect in narrowband or broadband?

Low frequency noise should require a lot deeper duct to be trapped because the cutoff frequency of the duct decreases with depth. Any sound waves with a frequency lower than the cutoff frequency won't "fit" in the surface duct and won't be trapped. Similarly, high frequency noise should not require as deep a duct to be trapped.

At some distance, even with a strong duct, you should still be able to detect because you're getting direct path energy. Also, if the duct is weak, it will leak more energy than a strong duct.

Actually trying to estimate the effectiveness of sonar in the ocean can get you a PhD in oceanography and physics because the answer is almost always, "it depends on a lot of stuff.."

[SeaQueen]

Originally Posted by Molon Labe

I'll have to play around and see if there are "strong" and "weak" layers in the game. Does the game choose the exact SSP profile at random within the specified SSP type, or does the exact shape of the SSP depend on things like depth and time of day or any of that sort of thing?

From what I can tell, it depends quite a bit on the bathymetry. I'm sure there's also a stochastic component as well.

It ought to also depend on the season and windspeed.

If you can imagine, in a summer month, the sea surface temperature is much higher, and it cools as you go deeper so the sound speed will be higher near the surface and drop as you go deeper. That would drive the sound waves down, so unless the water is deep enough so that pressure can dominate temperature enough to push the sound speed higher again, you end up with a bottom limited case. In the winter, the sea surface temperature is not so high, so there might not be so strong a temperature gradient. So maybe it's not as bad.

Additionally the surface duct depth probably ought depend on the wind speed some how too. Strong winds would create a deeper isothermal mixed layer, while low winds ought to make it almost go away.

My suspicion is, though that a lot of the interelatedness of the environmental variables isn't there in DW. I know there's no correlation between sea state and wind speed, for example. One could spend a whole lifetime developing a sonar model. With a little bit of research online, you can do a lot to make sure everything is set up the way it "ought to be." In order to have as accurate an SSP for the given scenario as possible.

[Bellman]

Speaking as a layman and with respect to those who I suspect know far more in real life about this topic,
it simply amazes me the extent to which we all endlessly speculate about what real-life elements of sonar
performance are included in the sim. Unless and until SAS expand on their somewhat brief manual exposition
we are indulging in a rather pointless exercise.

[SeaQueen]

Originally Posted by Bellman

Speaking as a layman and with respect to those who I suspect know far more in real life about this topic,
it simply amazes me the extent to which we all endlessly speculate about what real-life elements of sonar
performance are included in the sim. Unless and until SAS expand on their somewhat brief manual exposition
we are indulging in a rather pointless exercise.

Yeah... that's why I get really annoyed when people say things like, "the sonar ranges are too short [long]" and you never see anyone say what the SSP looked like, what season it was, what the seastate was, how deep the water was, etc.. The truth of the matter is that any estimate of sonar performance has to be qualified with an extensive description of the environmental conditions in which that performance was achieved.

Unfortunately, too often the only environmental qualification I see is that the detection took place in Tom Clancy land.

And if you really want to get into it, any good sonar model has to go hand-in-hand with a good global climatology.

In truth, outside of classified discussions, nobody really knows how good a given system will perform against a given target and that's how it should be.

[sonar732]

Originally Posted by Bellman

Speaking as a layman and with respect to those who I suspect know far more in real life about this topic,
it simply amazes me the extent to which we all endlessly speculate about what real-life elements of sonar
performance are included in the sim. Unless and until SAS expand on their somewhat brief manual exposition
we are indulging in a rather pointless exercise.

Here, Here!

[OKO]

let me give you a very good link about it :

http://www.fas.org/man/dod-101/navy/...P/snr_prop.htm

suggest you read that, than we continue talking about it
for our own culture and to know how to use it in DW

[LuftWolf]

That's a good read, OKO, for sure.

I've read it before and will read it again, now that it is very relevant to the sonar model we are now working with.

I've said it before and I'll say it again here... thank you SCS!

[sonar732]

Check this one out also!

http://www.fas.org/man/dod-101/navy/...s/uw_acous.htm

[OKO]

on your link, we could see the increase of dB when increasing speed is NON LINEAR =>

http://www.fas.org/man/dod-101/navy/...s/IMG00006.GIF


What I said for a long time ... when lots of people said it was linear ...
So we can consider the increase of the dB should be not as linear as the one in actual DW (with sound fix) nor than the one of LWAMI.
it's not + 1db per knots or per 2 knots, but rather near no difference at slow speed and huge one when increasing speed
like 2dB beetween 5 and 10 knts, and 10 dB beetween 15 and 17.

I remember how peoples said DW stock wasn't good here.
We could see now, stock DW was probably more close to the real thing than the actual values .....

THIS need a real new work.

[sonar732]

So, if we combine the new values in 1.03B with the original sonar sound vrs. speed issue we'd be in business!