Usually, the point of doing tests like yours is to find out what the model is. I'm not aware of any testing on the shape of the shadow zone in CZs, so you're breaking new ground. I did a little bit of testing with sonoboys a while back and noticed that generally cross-layer detections were a bit shorter in a CZ than an SD, but that didn't make any attempt to account for the depth of the buoy relative to the layer.

As for explaining it...I really can't. I'm looking at the SSP shape and I'm quite surprised that you're getting longer ranges near the layer boundary than you are when you're deeper. I would have expected exactly the opposite.

But one thing I would expect is a difference because in the CZ SSP once the sound gets below the layer it is going to curve out instead of down. I would expect the shadow zone shape to end up being similar, but it should (in my judgment) but pushed back further out from the source.

Pretty strange .. will try this too. Me previous test did not show anything like that.

I'd like to suggest to do future tests with narrowband. Reading the broadband can be quite subjective, especially for quieter contacts like submarines. It might take a few mintues of looking at the intermediate interval to realize you even have a contact present. With NB you get the line right away as long as you have the right bearing displayed.

With LWAMI you get contacts on the sphere on broadband before narrowband. Also since the shadow zone is "cutting off" sound, the contacts pop up on broadband quite bright and noticeable. But perhaps the SNR methode of the FFG towed array would still be the best methode.

BB is quite OK on these ranges.

I did the same test.

The problem near near the indicated layer depth (400ft in my case) seems to be that sub must be at about 415ft to feel the effect. This depth difference does not seem to be depending on the range and it was 15 ft for LA in my case. If you were 10ft bellow indicated layer depth, it should work like you have found.

I could not reproduce the deep problem. I can measure nice curve down the crushing depth, no anomalies.
Make sure the target sub did not slow down for some reason, it happened to me once, with no obvious reason. If it still happens, post the save.

To feel what effect?
I think if the layer is at 400ft and the sub has an indicated depth of 415 feet, it's possible that the sonar entity is above the layer. 415 feet is the depth of the keel, and 15 feet is what...two decks? How many decks does a 688I have? More than two I'd guess...

Dr. Sid, try this mission:

http://x7buza.bay.livefilestore.com/...st.mu?download

I attached the mission and not the savegame (which is abou 4mb large). So layer depth might varie, but I don't think it should make a difference. If it doesn't work I will uploade a savegame.


What you should see is a 688(I) screaming in at 32 knots and poping up on broadband at 1.4 NM.

LA diameter is 33 feet (10 meters). So yeah, sphere center is about 15ft from keel. That should be it.

Bohaha ! You have discovered second layer ! :up:

Check SSP in that game of yours. There is speed maximum, which DW marks as layer depth. Allright. And then, with covergence zones type SSP, the speed goes down and up again. Theres is minimum on that curve. In your case it's neatly on 800ft. As you got under 800ft, the signal was really bad.
With my tests this minimum was at 2000ft, I could not get there, so it did not show.
Why was that different ? Because of different latitude it seems ! In real this minimum, called deep thermocline, gets generaly shallower with higher latitude, and DW DOES simulate this !

This calls for another bunch of test and it can have MAJOR effect in latitudes above lets say 60 degrees.

Btw. in real, this minimal speed attracts sounds and forms so called deep sound channel. If listener is at this depth it should get GAIN on detection range especially if the sound source too is in this depth. That especially must be tested. I sugest about the same latitudes as your mission has, which is 67N.

Now this game is not dead ! It's not fully understood yet ! :arrgh!:

Edit: Anyway I don't see how this is realistic. As much as my sound simulation shows, it's not. Deep channel does not block sound.

You are right, the deep sound channel is actualy above 1000ft in that scenario. I didn't notice that because I used to think that the deep sound channel is unreachable in DW anyway.

It explains why dedection ranges were so small. In cross sound channel situations, the sound got cought in the channel. Still it seem to be a bit of an abstraction, as the sound got cut off in DW at a very specific depth, while the deep sound channel should be a rather fuzzy (the thermocline has a sharp edge in the SSP, the sound channel a relaxed curve).

Also I there doesn't seem to be any effect of actualy being inside the sound channel, where dedection ranges should be very long.

Still this is a rather important discovery. And it means that the deeper diving subs in DW actualy have a reason to dive deep and exploit the sound channel (even if it just works as an additional layer).

Interesting.... I'm guessing the Month will have some effect on that too...can't imagine why else it's listed in the Acoustic Conditions setting.

That sound channel depth caught me by surprise too. I'm also used to seeing them around 2000ft...or deeper. So it seems like what might be going on is that the sound channel, instead of being modeled as an effect that happens gradually, centered around the 800ft minimum SV, is a discrete layer beginning at the minimum SV. Anyone want to put the contact at that depth and see if the det range is a crapload longer than it is for a contact outside of the channel?

Like the other SSP features, it's a simplification rather than a realtime ray trace. But I'm thinking back to what you said about the sound paths being the same both ways. The sound channel tends to trap sound inside it; that should also mean that sound outside it has a hard time staying inside it (the sound that goes down thru it and then curves back up without being captured notwithstanding)

In my understanding the sound source does not need to be in the sound channel, as the sound gets cought in the channel eventualy anyway. But the listener needs to be inside.

Judging from my previous results and without any more specific tests I would say that you are right and we don't actualy have a sound channel modeled but just an additional layer at minimum soundspeed depth.

In real, the sound is trapped inside it if it is emited near the sound axis. If it is well above the sound channel, it will just go throught. Well better .. it's matter of the angle. Some part of the sound will always be trapped inside.

Depth of the minimal speed affects the shape of the front edge of the shadow zone, but just a bit, and actually in the opposite direction (it moves the shadow zone away from the sound source as the depth increases). It by no means can create second sound blocking layer.

Month also does affect ice amount at different places. Check the files IceWorld01.Dgd to IceWorld12.Dgd in DW's world directory.

Well, this thread gave me some motivation, so I did some tests about latitude and months. As it turns out, the month only does seem to affect the amount of ice generated in the polar regions.


However, latitude seemed to play a big part in the depth and structure of the deep sound channel. I conducted each test five times for accuracy.

In test one, I was centered at the center of the grid (0 deg latitude, 0 deg longitude). The DSC consitantly seemed to be at around 2000-2100ft in depth, with an overall low minimum SV at the DSC axis.

In test two, I was about 500nm SSW of Iceland, in the North Atlantic. The DSC still rose a bit to around 1800-1900ft in depth. The SV at the axis was also a little higher on average when compared to test one.

In test three, I was 260nm E of Jan Mayen (the tiny island north of Iceland). This was weird. There was no sound channel axis at all. Minimum SV occured at the surface, which rose quickly to layer depth. At layer depth, the SV's rate of increase dropped dramatically, but never actually went negative (the SV starts decreasing). It began a gradual increase from layer depth to the bottom of what the XBT probe could see, causing a gradual curve on the SSP chart. Here's a drawing of what it looked like:

http://i175.photobucket.com/albums/w142/ASWnut/SSP.jpg


-ASWnut