SONAR Folks: Acoustics model questions

[feld]

I am interested in writing DW campaigns using the LWAMI mod but I'm running into acoustic problems. I think they're similar to some that SeaQueen mentioned before here. I've read Sonalysts Game Design Notes (SGDN), played the game, and poked around the forums enough to learn alittle...
fair warning: All this means is that I am now dangerous enough to start actually asking questions

1. How does mission editor selected sea state affect ambient noise? I expect Wenz curves but cannot tell from the displays...
2. How does the weather selection change the ambient noise?
3. Does the model change the ambient noise based on the number of ships present?
4. I've noticed that the "bottom limited" setting sometimes produces a strong positive grandient and other times a strong negative one. Can anyone explain why?
5. Does the game model frequency cutoffs in ducts?
6. Does the game model the Deep Sound Channel? I see the beginnings of one on certain tropical/subtropical deep water CZ SSPs (e.g. Phillippine Sea, August, 1200, CZ shows a sound speed minimum below the thermal layer...now if I just had an ALFA to get down into it...)
7. How many bottom bounces does the propagation loss model compute? Or am I totally out to lunch and it's not a ray tracer?
8. Does the model use the month and time of day settings to adjust sea surface temperature?

If anyone has any insights, I'd greatly appreciate them...thanks!

feld

[Kapitan]

The main things that affect SONAR are quite simple, for example where i operate most of the time under the polar ice HF sonar is my greatest asset for navigation, the HF sonar picks up any ice bergs and polyna which i can surface through.
(polyna is a hole in the ice)

But due to the back ground noise the ice makes (due to constant movement) then i find that my SONAR equipment is not at its peak 100% level, and i cant detect submarines at far distances, unless i dive down to around 250 meters and sometimes that is not achievable.

There is a band of water there maybe 3 or more in one spot called a thermocline, this is where warm water and cold water meet to form an invisible cover so to speak, its difficault to detect a submarine if your above and its below unless you use my tricks.

Background noise such as large merchant ships or any ship for that matter can hamper detection whats even worse is if the enamy submarine is acctualy underneath that said vessel as the surface vessel will drown out any submarine noise.
But back ground noise in general can make you miss things on the sonar screen.

Another thing to consider is temprature of the water, sound travels faster in hot water than cold (unless its ice) this is because the monocules in the hot water are already vibrating alot and any sound is bounced along with the monocules therefore making detection easier in the tropics then in the bearents sea. (only small difference but it still can matter).

Water depth is also criticle, shallow water means slow speeds for many submarines, because the noise will bounce off the sea bed and go any where, this is generaly why littoral (shallow) water ops are left to the more suited SSK submarines such as the Kilo Type 209 and 212 or the Scorpene as they travel slower due to battery's and also thier powerplant makes less noise.

In littoral waters the use of the towed array is limited because at times you can wash it out due to the fact its acctualy dragging on the sea bed, so you have to rely on your hull mounted sensors, which again means your detection rate has droped by around 25% or more.

Thats just a low down on what you asked if you want more detail i could try and work it all out for you.

[feld]

Thanks for the input! I hadn't thought about ice noise...have you noticed if the time of year changes the amount of background noise under the ice? I haven't played up there much...

Have you noticed if in game background noise actually changes with shipping density like you mention below?

Originally Posted by Kapitan

Background noise such as large merchant ships or any ship for that matter can hamper detection whats even worse is if the enamy submarine is acctualy underneath that said vessel as the surface vessel will drown out any submarine noise.
But back ground noise in general can make you miss things on the sonar screen.

As near as I can tell from the tests I've run (all tests on a 688i, only using spherical array, in august, Western Pacific, bottom limited environment, at 1200 hours local time).
- Sea state plus self noise determines the "static" level that appears on broadband display.
- Self noise depends on speed and flow over the hull. So, when I raise masts or open shutter doors I get a step rise in the noise on my spherical array broadband display.

Now, I know that the # of ships present *should* raise background noise...but I have so far been unable to tell if it actually does. This seems important for missions in the chokepoint straits where shipping density is really high. Which is...after all...where the targets are

[Kapitan]

As im not a blue water skipper or a limited blue water anyways, i have found that in the winter months (its winter for around 9 months) the ice is not as noise as the summer months so the back ground noise differs very slightly.

The more traffic you have the harder it is to find contacts, i would personaly travel right under a ship then travel either side or away from it, it makes more tactical sence to mask your own noise using other traffic then it does to just go slow.

Time of year, weather, type of bottom mud and sand absord sound more then a rock bottom, thermoclines, polyna, iceburgs, sheet ice, plate ice, pack ice, temprature of the water, all affect noise levels and achostic frequencies.

August 1200 in the mid pacific would be probably be 28 degrees slight winds state 2 seas which would mean that noise will travel further then in february when its cold wet and what have you so yes it does change.

For me ive been diving akulas under ice since sub command verious times of year verious locations and the noise does change, im pretty good with navigation i have navigated some real tricky paths including the bearing straight (that alone took 27 hours) ive also navigated the kara sea into the laptev sea (that took 53 hours) the longest stint ive done was a trailing of a chinese Xia class SBN in the bearing sea area which lasted 8 days.

If your good at weather patterns tactics and overall patient then i would definatly advise you to come under ice, i will work around 35 meters 4 knots.

Many have said it doesnt matter what the weather is like on the topside if your under ice well it is because the weather defines how fast the ice will move or melt and how big the polyna is (use Shift + I twice to get a good ice map on the nav screen).

Background noise is diffrent where ever you go when ever you go it is always changing if you want more info about it just PM me or something.

Yes the more ships in the scenario the worse the back ground noise is, the worst are whales, you need to mark locate track and find out who is who once you done that you have a tactical grip on your situation there fore you need to then find the enamy i can do that in roughly 10 mins marking upto 50 ships and locate track and have master contacts on them.

If you increase the background noise by making your ship the emmiter then chances are you are just cutting your own throat, in the akula i can tell when some one has opened thier torpedo tube doors or raised a mast even in such subs as seawolfs, these little things can give you away to any one no matter how super quiet your sub is.

Golden rule is if you can hear them they probably can hear you, he who makes a sound first will die first.

in the last 6 months of playing single player ive tracked 2 seawolves 1 688i 1 ohio 1 trafalgar 2 rubis and more then 350 surface ships, with 98% sucsess (was counter detected 4 times).

When i deployed to the med i ran under the nitmitz class carrier John C Stennis i tracked her for 8 hours then decided to run ahead and take pictures, hgowever i got my calculations badly wrong and in the end the 91,000 tonne carrier just ran over me.

If you place your vessel so that your propellor is just under the surface ships propellor the surface ship will cancel out your noise (as its louder) so effectivly you are not there, this means that you can then havea better advantage in terms of quietness but also a weaker one in detection.

A good tactic to use to beat waiting submarines who want to track you also a good tactic for beeting sosus and surface ships who are also trying to track.

any more info please PM me