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.

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/uploa...s/0621/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/uploa...621/analog.jpg http://img0621.paintedover.com/uploa...0621/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/uploa...0621/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.

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.

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.

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.

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.

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

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

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

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

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 !

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.

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. ;)