A curious thought on DW passive sonar detection range

[SeaQueen]

I never said SSP had no effect on low frequency sound, just that the surface duct might not have much of an effect on it, depending on what the frequency is and what the duct depth is.

Originally Posted by Dr.Sid

It's not that frequency dependent effects are impossible or would require complex simulation. We don't need to be much true to the real world, we don't design real-world sonar set or something. We just need to catch the basic nature, the most important factors.

That's fair, the thing is, it's sometimes hard to make a decision about what's important and what's not.

Which again reminds me one cool idea. Sonar is about listening right ? Even these days. Then why the hell does DW use few samples for all that boats and subs ?

Actually, in my experience, the sonar sounds in DW are pretty realistic for the boats and subs. That's what I remember them sounding like. It's basically just broadband noise.

Why those samples are speed independent ? Why there are no transients ? It would be great fun to be able to HEAR: 'it's typhoon, doing lets say 10 kts .. ah ! changing depth now .. opening silo hatches !'

I don't have any direct experience with this, but my sense of things is that the sonar operatator has a hard time telling how fast something is going just by listening. They might make a guess based on past experience, intelligence, or even just bound the problem by saying, "here's how fast he can go, here's how slow he can go," and judge from bearing rate, maybe. Doppler will give you a sense of relative motion and DEMON will tell you the speed, but I'm skeptical that a sonar operator can get much more than a vague sense of how fast something is going just from listening.

Transients would be a nice thing to have, but again, it's not clear to me how you'd do it. What would be the transient's source level? What would be their frequency? What about broadband transients? It all seems very hazy. You'd have to make a lot of assumptions about all the funny little pumps and motors and hydrolics that make a submarine go. I don't know what frequencies a hull creaks and groans at when it changes depths.

[PeriscopeDepth]

Anyone ever play Fast Attack? Had both transients and your sonar operator would call out "Contact Sierra 12 is changing depth!" Can't attest to how well it was implemented, but it was pretty cool.

PD

[SeaQueen]

Yeah... usually what they do is not worry about how the transient sounds or ends up on a lofargram, or whether or not the operator recognize it. Instead, they just assume that somehow they are detected, and then then have some kind of indicator that they are. Red Storm Rising also had them. Not for changing depths, but there were launch transients.

Originally Posted by PeriscopeDepth

Anyone ever play Fast Attack? Had both transients and your sonar operator would call out "Contact Sierra 12 is changing depth!" Can't attest to how well it was implemented, but it was pretty cool.

[Dr.Sid]

Here's how i'd do it. I'd make sound effects first. Sound of pump. Sound of hatch opening. Something which is actually played in DW for the player to get the atmosphere.
Now all I want is that this shows on sonar too. BB and NB. I can do FFT of these sounds easily (and ahead), and for example ogg sound format which is used in OpenAL has in fact FFT analysis already done, only question is if I can access it. Anyway I did FFT before, it's no big deal.
Then also, of course, the transmission loss simulation (I mean approximation) must simulate how the frequencies are filtered. This filter must be applied on the FFT of the sound before displaying it on the NB screen, that is easy.
This filtered sound must be replayed into earphones, which too is possible and simple with OpenAL.
Like that you could let the enemy sub sing russian anthem, see it on NB, hear it in earphones, both affected by frequencies lost in underwater transfer.

As for the sonarman telling speed, yes, that was bad example, especially for the sub. Anyway I wanted to say that sub games these days don't model the sounds much well.
The sounds may sound 'correct' in DW. But the sound does not change with speed. There are only 2 or 3 sounds for all surface ships !

Look at IL2, the later versions. Engine sounds different for each plane. The sound is different from different angles. It is dependent on RPM, of course. Every damage to the engine can be heard. You got some hits .. then you LISTEN to the engine .. and you decide 'it sounds ok, I'll make it to the base !'.

And in IL2 it is mere sound effect. In subsim game this should be basic part of the game, I think.

[Hitman]

IIRC whales can communicate over huge distances, and they are basically just yelling in ultra low frequencies...

Seaqueen is right, given the proper conditions, anything can be possible :hmm:

[Dr.Sid]

I gave up on the parabolic equation. Anyway I created simple system for waves animation (I mean sea waves), and I found that it behaves well and that sound speed profile can be easily used with it. It has many problems and it's not suited well for sound simulation, but I could demonstrate few things. Check this out.











These shows sound propagation in sound channel with both bottom and surface reflection (in fact all borders reflects the sound, the right just a bit since the sound is weak there - it's one of the problems of this method, all borders reflects at 100%).

Frequencies are 4,8,16,32 and 64 pixels (size of the simulation is 100x500 pixels). SSP is very strong sound channel with axis exactly in center of the picture. It's completely out of scale, but it's wave-based sound propagation model and it shows how frequency affects things.

This actually animates the waves from the source, so you can see front-face moving through the medium and slowly (very) carving the shapes.

Anyway the best thing about this is I understand waves bit better now and I'm getting closer to understanding that darned parabolic equation

[Castout]

Ouch my head hurts

[OneShot]

"Impressive ... most impressive"

[goldorak]

Originally Posted by OneShot

"Impressive ... most impressive"

You forgot :rotfl:

[OneShot]

Right guy ... wrong picture. He said that when Luke jumped out of the gas freezing chamber ... but I'm digressing.

[goldorak]

Originally Posted by OneShot

Right guy ... wrong picture. He said that when Luke jumped out of the gas freezing chamber ... but I'm digressing.

Yes but I didn't find that scene sorry.

[feld]

Originally Posted by Dr.Sid

From my experience:

- AFAIK, in DW, shallow water does not affect sound travel, except for terrain blocking the signal. But I guess it should block everything or nothing, it should not weaken the signal.

Dr. Sid,
Have you ever been able to confirm that terrain blocks sound propagation in DW?
-feld

[feld]

Originally Posted by SeaQueen

You know... back in the day, much was said about how sonar could detect things at ranges of hundreds or sometimes even thousands of miles. That's still true. The thing is, it all depends on the target and the acoustic conditions at the time. People don't like to believe that the really is that much variability but there is. In the '80s they were worried about hordes of NOVEMBER class submarines forcing their way through chokepoints in the northern latitudes, now they're worried about smaller numbers of KILO class submarines in tropical and subtropical latitudes. It's not that the sonars have changed, is that the environment and the targets have.

Amen!

I want range & frequency dependent propagation loss !
@ SeaQueen : are there tabulated solutions to the wave equations? Dr. Sid might be able to use a lookup table?

-feld

[Molon Labe]

Originally Posted by Feld

Quote:
Originally Posted by SeaQueen
Quote:
Originally Posted by Molon Labe
According to most publications, RL detection range is far shorter than in DW now. So, NO.


You know... back in the day, much was said about how sonar could detect things at ranges of hundreds or sometimes even thousands of miles. That's still true. The thing is, it all depends on the target and the acoustic conditions at the time. People don't like to believe that the really is that much variability but there is. In the '80s they were worried about hordes of NOVEMBER class submarines forcing their way through chokepoints in the northern latitudes, now they're worried about smaller numbers of KILO class submarines in tropical and subtropical latitudes. It's not that the sonars have changed, is that the environment and the targets have.


Amen!

I want range & frequency dependent propagation loss !
@ SeaQueen : are there tabulated solutions to the wave equations? Dr. Sid might be able to use a lookup table?

-feld

The DW acoustic model already has those.

The problem were up against as modders is that the acoustic model is outside of our reach. Unfortunately, we can only play with source levels and sensor sensitivity. So we have to choose a range of ranges within a fixed subset of what could occur in RL. I think they way things are now we've set the bracket on the high side of what might be the median, based upon publications and upon comments of submariners posted here. I'd be absolutely shocked if LWAMI ever acted shift that bracket higher (by "enhanc[ing] passive sonar capabilities").

[Frame57]

Hmmm! I wish I were a Sonar Tech, so I could add to this. But I was assigned to our 'tracking parties' while on the A-fish. We had no problems at all finding outbound boomers from the former Soviet Union. We would track em for weeks and make SSP's on them. I seriously do not think this game comes close to reality for many reasons. I cannot get a boat to perform anywhere near as well as our old cluncky 637 class boat did. It makes me wonder if they modled the sonar after paper cups and string attached to the hull.