Detection Range Glitch?????

[swimsalot]

Ok, need some professional adice on detection ranges.
Recently have noticed that a player consistantly seemed to be able to acquire other players very quickly, at long ranges.
Unnamed player would be in an Akula, others in SW.
Having heard about this happening to other players, I was curious as to how it was happening. Not worried about a cheat, I was worried about my own skills.

At 15-20 minutes into the game, Akula would fire missile torps at Sw, landing them within 700yards of where the SW started mission.
Sw usually wasnt there anymore, but pretty close- close enough to kill the SW 4 out of 5 times. Not bad.

Since I was bored, and a little suspicious, I replayed the map.
It's a busy map, 3 cargo/car carriers in the area, 20nm circle. A few trawlers outside the circle.
1 Akula and 1 SW inside.
Akula was 19.1nm from SW, both at about 190 feet, both speed 6kts.
Layer at approx 370 feet.
SSP was rock bottom, SD.
Sea state was light chop, daytime.
The Akula apparently picked up the SW at 19,1nm, and at 14minutes fired a salvo of missile torps at him, which he narrowly evaded. taking into account the time needed to stream the array, acquire and mark contacts,preset, and fire, I thought 14minutes was pretty damn fast for 19.1nm range.

I had the mission designer that made the original map set up a new map with 3 subs in it, same size and SSP, no neutrals.

All subs started at 192 feet, 6kts, above layer that was at approx 500feet.
We then spent a few hours checking detection ranges.
We found a curious situation, which bears further review.

At beginning of mission, for the first 4-5 minutes, I was able to hear the SW, which at the time was 48,000 yards away. Clear solid 60hz line.
I could hear the Akula at 38,000 yards, with clear line at 50hz and 125hz.
Seemed a little far away for a good track on a SW.
The Akula tracked both Seawolves at mission start, 1 at 38,000 yards, other at 44,000 yards!!!!!

So all subs were able to hear contacts at 44-48,000 yards at mission start.
Wierd thing is that 5-10 minutes into the mission, the contacts disappeared, or got alot quieter.
But the auto -TMA kept tracking the contacts, updating lines on the TMA chart!!!
I had my Gamma settings tweaked up by Powerstrip, so I can see even the faintest contacts.
We didnt slow down or head away from each other; I closed range on the SW until I re-acquired him at about 38,000 yards.
This would be where I would expect to hear a SW at 9kts.

So why could we ALL hear each other, at these ranges, at mission start, but not 10 minutes into the game, if no changes had occurred to speed or depth?

Is 48,000 yards detection against a SW, by a SW, too far?
Is 44,000 yards detection against a SW by an Akula to far?

I have the map our designer made if you would like to try it out.
Nothing fancy, should be easily reproduced.

I think this unnamed player has figured out that if ya get a contact at the very beginning, auto-TMA will track it even if it's not visible to you.
And initial detection ranges at start are far in excess of what I thought were normal ranges.

1 time random thing? Maybe, except the unnamed player did it a handful of times. And we were able to reproduce it, I ran it 2 times myself.
A glitch in the code?
(we were running plain 1.03, no mod.)

Thoughts?


NOTE- I am specifically NOT accusing anyone of a cheat- I think there is a glitch in here that someone figured out.
(sorry fpr length!!!)

[TLAM Strike]

Sorry to say but we've heard this before:
http://www.subsim.com/phpBB/viewtopic.php?t=51872

[LuftWolf]

Was the SSP by any chance, a convergence zone?

Because that is the behavior you are describing, if we are to assume that the game is functing properly.

[swimsalot]

TLAM: I read that other thread when it came out. It has nothing to do with what we re-created. I don't think this is a cheat, and we made the map, so there is no worry over mission triggers.
We weren't in our baffles, nothing that simple.

As anyone that has played with me would know, I am not inexperienced with this sim. I understand when a sub should be there, and when it shouldn't.

LW:The designer that made the map tried it with a few different variations (ie SD, convergence,etc) all had same result.

Please, could someone with vast experience run the same setup we did and try to duplicate this?

[LuftWolf]

How about posting the setup at the CADC?

[swimsalot]

RGr, will try to post it now

[Fish]

TLAM: I read that other thread when it came out. It has nothing to do with what we re-created. I don't think this is a cheat, and we made the map, so there is no worry over mission triggers.
We weren't in our baffles, nothing that simple.

As anyone that has played with me would know, I am not inexperienced with this sim. I understand when a sub should be there, and when it shouldn't.

LW:The designer that made the map tried it with a few different variations (ie SD, convergence,etc) all had same result.

Please, could someone with vast experience run the same setup we did and try to duplicate this?

Swims, I like to try that map on my LAN. I think the original map is from Mf?
I was talking with him yesterday about the "glitch" and made a map for LWAMI to do some tests.
I can't get something like wise with the mod, I can see the Akula (while in the Seawolf) at 6 knts 12 nm away, but I can't see the Seawolf (from the Akulas side) other then when the SW is at a speed of 13 knts or more.
Fish.

[Bellman]

Swims: Confirmed your findings with that scenario in Stock. Dived SW which gave immediate TA SNRs of 1 on the other
SW (22nmn) and Ak (21.5 nm) Within 4 minutes faint base tonals allowing trackers to be assigned. ATMA then
switched on and off and with manual assistance by WF the solution on the Ak (No Truth) was 2.8 nm out.
Ak NB+ ATMA proved just as farsighted. In Ak NB I had SW(A) at 20 nm and SW(B) at 21.5 nm. The above was a typical
playing of this scenario and the other reruns followed the same pattern................The ATMA cheats !

I noted on replaying the mission several times that the starting positions were not randomised adequately.
The SWs random boxes are only 1.5 nm square and the Ak has a fixed starting position ! Note also that the Ak
starts with TA deployed but the SWs are not ! As I proved after only half a dozen runs
anyone familiar with this scenario and its 'peculiarities'would have a distinct advantage over opponent/s. :huh:
But on the other hand all subs enjoy the same super receptivity so the scenario creator only enjoys normal priviledges.

Another thing briefly - could the topography influence receptivity dramaticaly in this case ? The Aks position is
at the focal point of a sound bell - the shaping and the depth of the seafloor creates a perfect megaphone
and/or receiver shape. It might have a bearing on sonar performance ?:hmm: Perhaps the limited
range of starting positions seeks to maximise this feature ?

I am sure RADM Fish + Lan will provide a more informed second opinion. :yep:

[sonar732]

Was the culprit the hoster?

I hosted a mission once on gamespy and an unnamed person sent me a message to SHIFT+CTRL+T (show truth for those who don't use hot keys). I played dumb and asked him why and he didn't reply back.

[compressioncut]

Well, without knowing the bottom depth it's not possible to know for sure if CZ was present, but the ranges sound short for an in-layer contact. They are closer for submerged CZ but the subs were in the layer. As well, in the game you normally have to force a CZ SSP to get CZ above layer.

And assuming that cutoff frequency is modelled, the 50 or 60hz tonal probably should not have been ducted in a 370 foot layer. Depending on the magnitude of the duct. I'm just guessing cutoff would be around 170hz, but again, I don't know the duct's magnitude (velocity at surface versus velocity at sonic layer).

But, a rock bottom and 20 mile ranges sounds very suspiciously like bottom bounce. If a rock bottom in game is modelled as smooth rock then its not completely out of the question, as bottom bounce is a path a lot of people don't account for - there's little absorption or scattering from smooth rock. And it will behave similarly to a CZ, except calculated ranges could be a little out (as you experienced).

Still a little weird for state of the art subs to detect one another 20-25 miles away. I suspect it's something to do with the environmental modelling, in that there is probably not a great deal of ambient noise like there is/can be in the real ocean, especially at very low frequency.

[Bellman]

Well when diving the SSPs Isovelocity over negative - Surface duct and mud bottom ! Layer at 550-600ish ft. variable.
(All subs above !)
With this split-beam pattern I wonder whether the topography could enhance the surface ducts receptivity range ? :hmm:

[swimsalot]

The map I posted at tha CADC is just a test map based on the same sonar conditions in the map I was concerned about; the designer didnt make random start areas, etc for the test map.
The original map was a mp map with same SSP, but with neutrals, bios etc.
Again, all I noticed was that the detection ranges seemes a little long, particularly for the Akula.
And the fact that they faded at about 4-10 minutes every time irregardless of ownship speed or target speed.
Thanks for the info guys, this is a good learning situation either way!

[Mcfester]

I noted on replaying the mission several times that the starting positions were not randomised adequately.
The SWs random boxes are only 1.5 nm square and the Ak has a fixed starting position ! Note also that the Ak
starts with TA deployed but the SWs are not ! As I proved after only half a dozen runs
anyone familiar with this scenario and its 'peculiarities'would have a distinct advantage over opponent/s. :huh:
But on the other hand all subs enjoy the same super receptivity so the scenario creator only enjoys normal priviledges.


The map you tested was a test map taken from the original mission map, all neutrals, bios, and dynamic start locations removed and subs placed in same positions as they started in the mission that was played where the problem was first noted.

[OKO]

... I wonder whether the topography could enhance the surface ducts receptivity range ? :hmm:

confirmed, bellman
Bathymetry is a very complicated thing really ...
But there is a very usefull tool to use it : SHIFT + I on the nav screen
With this shortcut, you could switch beetween "depth+SNR", "SNR only" and "nothing"
3 selections.
If you want to find the best place around to listen, use SNR only with SHIFT + I, and use the darkest area next to you : here you will have the best SNR you could find around, so the best listening capabilities.

If one ship is on a very dark area, and the other one is on a bright area, the one on the dark zone could detect first the other, because he is in a more quiet water and could hear at longer range, when the other have his sensor perturbated by a bad SNR.

Topography have great influence on SNR, you could see this because there is only few difference, usually but not always, beetween relief and SNR.
But it could be VERY different on some places.
I had maps where it was completly different, where dark areas were often shallower than bright areas !

One often believe that the darker the area, the deeper the water, but that's not always true, and sometimes completely false ! (see some shallow area around filipines)

So, to avoid any misinterpretation, if you look for the best area to position yourself for detection, use SHIFT + I to find the darkest area near you.
And it's not always the deeper places !

[Bellman]

OKO: Perhaps we should distinguish between the ''complicated'' RL and what is present in DW. (good though it is)
I am very familiar with that ''tool'' ! But your lecture will be appreciated in some quarters ! :huh:

You should be aware that the copy of the scenario now available at CADC is not the original one. It has been
swapped for one which exhibits none of the characteristics observed by Swims or from my runs !

Edit - See below

[OKO]

OKO: Perhaps we should distinguish between the ''complicated'' RL and what is present in DW. (good though it is)


I was talking about DW
Real sea is even more complicated than that !
you don't have bathymetric areas on your map IRL
It's close to be a cheat in fact ................
lets say it simulate a superior bathymetry assistant, just getting out of 15 years of school, and able to calculate where are the best SNR areas around ....
Hmmm, I don't even convince myself with that argument ... hmmm :hmm:

[OneShot]

As for the "swapping" of the map over at the CADC please read my comments there ...

http://www.orionwarrior.com/forum/showthread.php?t=30183

In short, if this map was swapped then it was by either me or Swimsalot and I certainly did not do it (and it is in doubt if it was swapped at all ... see comments).

[Bellman]

OS - Yep I posted at CADC.

It looks as if it was another result of the LwAmi install which got screwed on Saturday giving odd Playtest UUV results.

**Sorry, it looks as if the second scenario file I downloaded was corrupted. ( how :hmm: )

**So my original findings stand (See below)

** Edited 24 th.

[Fish]

OS - Yep I posted at CADC.

It looks as if it was another result of the LwAmi install which got screwed on Saturday giving odd Playtest UUV results.

Sorry, it looks as if the original scenario file was corrupted. ( how :hmm: )

Exits stage left to play Ghost Recon AW for a few days. :lol:

In my opinion the game changes the SSP everytime you enter the map, just a litle. So the outcome could be totally different.

[Amizaur]

In my opinion the game changes the SSP everytime you enter the map, just a litle. So the outcome could be totally different.

Yes, that's the reason that whenever possible (no database changes) I did tests not starting a scenario multiple times, but starting it once and then restoring from save multiple times.

[Bellman]

Between 'executing' headshots in GRAW I have revisited this matter and my original findings stand as it was the second downloaded file that became corrupted. The one tested is the one at CADC.

Fish: Screenies of several dives show that the on- board ISP indicator in sonar shows widely different ISPs
and layers from each subs perspective. The Nav screens dumps of the simplistic (Sh+I) did not change ( as expected !)

What Swims asked, and I dont think anyone has answered fully, was what contributed to this wide range of
sonar fluctuations and the disappearing tonals. It should be noted that in this scenario the ISP & layer conditions vary dramaticaly and the topography makes a large contribution to these effects.

[Fish]

You start positon in the CAD map is shallow, when you change depth shortly after start, which many people do, me for example after looking at the SSP indication window, you should see a great differents in detection range. Maybe they changed there depth? :-?

About OKO's dark and light area's I doubth he is right there in his explanation.
When he first came with the idea the dark spots are hotspots for listening I did numerous test, but could not find prove.
On the other side, you could prove the opposite as shown in the pics below.

First a Seawolf listening at a worse place (light).



http://home.hccnet.nl/wico.p/Detection4.JPG


I was able to assign a tracker on a faint 60 hrz line.


http://home.hccnet.nl/wico.p/Detection3.JPG

Now the other seawolf at the "right"place (Dark)

http://home.hccnet.nl/wico.p/Detection1.JPG

Nothing, not a blip!

http://home.hccnet.nl/wico.p/Detection2.JPG

[Bellman]

Fish: I agree the subs in my dives which established contacts at over 20 nm were in the bright areas. As a matter of fact the contacts were in bright areas also (just). Almost looks like a simple mathematical progression. (But why ?)

The Ak is situated well inside a large 'bright' area whilst ths SWs are near the edge of 'dark' areas and its likely the divers progressed into them.

XBT readings taken shortly did'nt differ from the startng ones, as usual, but were taken at or near the opening depth.

[compressioncut]

There's a possibility of topographical noise stripping there, as 60hz is right in the sweet spot of distant shipping on a Wenz curve. The depths look plenty deep for CZ propagation, too. But again like I said earlier, I don't know what the ambient noise modelling is like in the game (I would suspect it's based on Wenz curves though).

In other words, the sub in the shallower water is seeing ambient noise from distant shipping stripped off, while the sub in deeper water is still seeing it, so the signal to noise for him is significantly poorer.

In other words I don't think that upslope/downslope propagation, like you guys are postulating, is particularly relevant here. The water is quite deep, whereas that phenomenon is more likely to occur in slope/shelf areas as far as I can recall.

[Bellman]

CC: 'Sloping/shelf' is what we have here with a focal point at 100 ft and the sea bottom valley gently sloping down to 3500 ft. Its like half of a cone with the Ak at the point. That must surely contribute to some 'amplification' effect.

This initial 'amplification' effect will be negated by the SW to the North diving (probably) behind the seamount to its South. Also both the SWs sit at the edge of changing receptivity as shown by the Nav area shading simplification.

A fascinating location with some pretty interesting potential exploits. The scenario designer made a skilful choice. :|\

[LuftWolf]

Interesting.

I'm glad the shadow zones are working now. :up:

Ok, note to self: go to the light.

I'm not sure the analysis is as complicated as some are making it out to be.

[Bellman]

:lol: But ''interesting'' still. ;)

[swimsalot]

Wow, great info guys, thank you for the help.
There must be more variables involved than I suspected, which is why I didn't think it was a cheat, just a curiousity.
Has anyone confirmed the info about "light" areas vs "dark" areas in terms of sonar detection ranges?

[compressioncut]

CC: 'Sloping/shelf' is what we have here with a focal point at 100 ft and the sea bottom valley gently sloping down to
3500 ft. Its like half of a cone with the Ak at the point. That must surely contribute to some 'amplification' effect.

This initial 'amplification' effect will be negated by the SW to the North diving (probably) behind the seamount to its South.
Also both the SWs sit at the edge of changing receptivity as shown by the Nav area shading simplification.

A fascinating location with some pretty interesting potential exploits. The scenario designer made a skilful choice. :|\

What's the bottom type? Smooth rock? What kind of bottom loss modelling is employed? This sort of stuff is very important.

Because to get the upslope/downslope focusing/megaphone effect you need to have at least reasonable bottom bounce conditions. But 10-15kft is very deep for more than one or two bottom bounce annuluses (annuli?), whereas true upslope/downslope tends to take place in much shallower water - the slope/shelf I was referring to was the continental one.

Moreover, downslope is more effective by far, whereas in the screenshots it's the sub upslope having better success, which in my opinion points to a TNS situation. Although at ~11 miles, I think the detection path was surface duct (much too short for CZ).

Without some sort of game-related range prediction program, or knowing how the game handles various factors (noise level, bottom composition, etc), all we're doing here is making guesses.

And, something just occured to me as I was about to hit submit:

The sub in deeper water may just be missing the downslope enhacement by virtue of being quite shallow, whereas the sub in the shallower water could be picking up the upslope effect given a bottom type with low loss characteristics. Intermittent contact would sort of point to that situation.

ASW is fun :|\

[XabbaRus]

I'd like OKO to explain how he came by his conclusion.

It is interesting as I had heard it before. I can't recall Jamie saying anything though.

[compressioncut]

OKO: Perhaps we should distinguish between the ''complicated'' RL and what is present in DW. (good though it is)

you don't have bathymetric areas on your map IRL
It's close to be a cheat in fact ................


You most certainly do! Bathymetry is a huge, monster part of real ASW planning. You know immensely more about the ocean bottom in real life than you do in the game.

edit - also noticed that the bottom type in this scenario is mud, and if it's behaving close to how it should bottom bounce is not the preferred propagation path (unless it's a thin layer over rock or something), so I'm leaning more toward TNS.

[compressioncut]

Okay I finally downloaded and played the mission, although I added a frigate for me to drive. I placed the skimmer on the other side of the subs, although downslope of the Seawolf.

I gained initial contact with the tail on the Seawolf at 10nm :huh: Tail was right in the middle of the surface duct, 500ft - SLD at 1136ft. 2,500 feet cable scope at 7 knots.

First of all, the SVP seems pretty unlikely. I dropped one BT from my ship at mission start in about 10kft of water to establish sensor placement, then once I was in contact I sent a helo out to put a BT on top of the ridge the sub was on (water depth there being not much more that 1300ft or so).

edit - something that bugs me is that you can't see the complete SVP from surface to bottom. In actuaity you can merge your shallow profile with a full profile from a worldwide historical database maintained by any number of agencies, if you don't have a probe that can go deep enough. That is fine and useable because the deep ocean doesn't change much.

http://img0621.paintedover.com/uploads/thumbs/0621/svp.jpg (http://paintedover.com/uploads/show.php?loc=0621&f=svp.jpg)

Now, I wouldn't expect an SLD that deep in low latitudes like that. Maybe 300 feet with the light sea in the mission as built, probably even shallower.

Nevertheless, we are working with what we have. A duct of 1000+ feet is perfectly happy to contain fairly low frequencies, like the first tonal on the Seawolf, whereas in reality with a thin layer (which the sub would not be in), you'd not see it outside of CZ. Although again at this latitude he'd probably be bottom limited depending on his depth (which could then produce submerged CZ and force me to think hard about sensor placement).

The problem the Seawolf is having is that he is on top of that ridge and can't get below the layer without hitting dirt. There is likely a little downslope enhancement working in my favor, too, although the primary thing happening here in my opinion is surface duct.

Anyway here's my contact early on plus a show truth of the same time. Didn't take too long to get a good track although I couldn't actually see the tonal:

http://img0621.paintedover.com/uploads/thumbs/0621/analog.jpg (http://paintedover.com/uploads/show.php?loc=0621&f=analog.jpg) http://img0621.paintedover.com/uploads/thumbs/0621/truth.jpg (http://paintedover.com/uploads/show.php?loc=0621&f=truth.jpg)

And the final disposition where I had a DICASS pinging him and could've put a fish on him at any time:

http://img0621.paintedover.com/uploads/thumbs/0621/final.jpg (http://paintedover.com/uploads/show.php?loc=0621&f=final.jpg)

The only glitch as far as I can tell is that the game's SVP is too generous. I'm going to change it to CZ and try again.

[LuftWolf]

Keep in mind, it is *the responsibility of the mission designer* to set the environmental conditions correctly for the geographic region, climate, time of day, weather, etc.

The sim only takes the parameters from the database and the mission file and runs the math... junk in junk out.

[compressioncut]

Keep in mind, it is *the responsibility of the mission designer* to set the environmental conditions correctly for the geographic region, climate, time of day, weather, etc.

The sim only takes the parameters from the database and the mission file and runs the math... junk in junk out.

Yup, and the SVP in this case is probably innappropriate. That said I'm not too sure of anywhere you'd find a 1000 foot mixed layer outside of some large winter storm in the mid latitudes. In that case ambient noise would be a big factor too, you wouldn't get a "magic" situation like this one.

Then again I may be only half right because I can't see the whole profile. I would hope the BT stops right about where the deep sound channel axis is (where it goes positive again). If so and given enough depth excess there could be above-layer CZ present in this scenario too, given the very deep layer. CZ ranges would be shorter that real ones tend to be in that case too I think. I held continual contact though so I was definitely exploiting the surface duct.

If the SVP continues negative all the way to the bottom (in this depth of water) then well, we have bigger problems.

[LuftWolf]

Yes, then it sounds like the mission designer should have set the SSP as a Convergence Zone rather than a Surface Duct.

In order to limit the under layer ranges, the mission designer could have set a sand bottom, which in deep water would mean essentially no bottom bounce, and to limit the above layer ranges he could have set a high sea state.

The sonar model is definately an abstraction. That having been said, there are enough parameters that can be tweaked to give the kind of setting the mission designer has in mind in terms of acoustic detection ranges, which seem to be at the heart of any sonar discussion on SubSim.

So, with regard to that one very particular issue, the mission designers should be able to get the settings exactly as they want, if they keep in mind all of the factors that go into it, including shadow zone modelling.

[compressioncut]

Okay I changed the SVP to CZ and placed the sub of interest below the layer (which was still a very generous 400 feet - there is actually almost no layer in the area in reality), at 600 feet. I also changed the bottom type to sand.

I placed my array at 600 feet (I think 2,900FCS @ 6kt) and opened the contact. Right at 30 miles I got the 60hz tonal in the first CZ annulus, and it was even visible on the display, until of course I crossed the outer edge of the annulus and it faded out.

Very much what you would expect in an ideal blue water situation. The other Seawolf on the other side was shading itself nicely, using topography to strip it's CZ.

[Fish]

Whow..., testing a map, I got a clear 60 hrz line from a 6 knts Seawolf...26.5 nm away, with LWAMI? :o
Could not redo it?
SD, with layer at 1112 feet, in my later attemp's the layer was less deep.

[LuftWolf]

Convergence zone detections have happened for me up to 40nm.

In the case of a convergence zone, the range vs. detectibility curves are NOT at all linear, and the specific depth of the layer and bottom play a big part in this.

If this map was not using a convergence zone environment... well then I don't know what to say other than make a mud or sand bottom if you want the range to be much less.

Cheers,
David

[Bellman]

'That' mission had a mud bottom which compounds the mystery.:hmm:

[Fish]

SD=Surface Duct, and yes (Bellman) mud bottom.

http://home.hccnet.nl/wico.p/Surface duct.JPG


http://home.hccnet.nl/wico.p/Contact.JPG

http://home.hccnet.nl/wico.p/Show truth.JPG

[LuftWolf]

Gosh, that's a long way... although it is in the surface duct itself. I suppose depending on the depth of the layer, this would be quite the echo chamber, although its even raining with a moderate sea state.

Well, I guess this is a good reason to test missions well.

Cheers,
David

[OKO]

About OKO's dark and light area's I doubth he is right there in his explanation.
When he first came with the idea the dark spots are hotspots for listening I did numerous test, but could not find prove.
On the other side, you could prove the opposite as shown in the pics below.

First a Seawolf listening at a worse place (light).

I conduct tests and you are right about this thing : "About OKO's dark and light area's I doubth he is right there in his explanation" but wrong about that one : "On the other side, you could prove the opposite as shown in the pics below"

I mean, the blue and dark area are NOT SNR relative ...

If you zoom out on an area where there is lot of blue/dark change (indonesia for example), then use SHIFT + I, you will see ... bright / dark areas are just hillsides of ground relief !
the lower depth is always at the separation.
So this is definitly NOT SNR relative.
I tought it was, from SC where you also have this feature, and didn't tested it from that time ! arfffff :88)
It's just to let you see better the ground relief because geodesics are not enought accurate, just a graphic feature !

[OKO]

SD=Surface Duct, and yes (Bellman) mud bottom.


Well, Fish, in SD, concerning the sound propagation for contacts in the upper layer, the kind of bottom have no effect.
For bottom limited of course, but also for CZ, where there is propagation under the layer, bottom is important.

It's different if contacts were under the layer of the SD ... but in the upper layer, it's a real concentration of the sound from emitter, snaking beetween the surface and the layer.

http://okof4.free.fr/images/DW/SDeffects.gif

In fact, 2 contact in the upper layer of a SD should have the best detection range you could find anywhere else, EXCEPT compared to 2 contacts in the same sound channel of a big CZ.


I'm finishing at this time a long mission (during a week) with CZ.
During the ingress I had contact at more than 40 miles for some minutes then they disapeared and reapeared at near half the distance.
CZ seem to be very well modelised.
1st detection at the longest distance you could detect something in DW, and second detection at less than the distance I could have detected the same contact in the upper layer of a SD.

[Fish]

With all due respect OKO, I am talking about LWAMI, not stock DW.
I learnt sonar from a real sonar wizzard, back in 688(I) Sub Command times, and am aware of the surfaceduct therefore. :know:
Still learning though. ;)