[Dr.Sid]

- Close in sound does not behave as a planar wave at all, wavefront curvature effects are extremely important.

I'm talking about masking distant noise .. thats why I used planar waves. What else do you sugest ?

- The amount of shadowing and diffraction is very frequency dependent.
- Broadband sonars don't operate on a single frequency, but instead the average amount of energy in a band.

That's what I'm talking about. This is simulation for frequency with wavelength of size of the object. Lower frequencies will be masked less, higher will be masked more.

- Broadband sonars have complex autogain and normalization algorithms that affect how the data will appear to the operator.

Is the autogain different for different bearings ? I seriously doubt that, except for things like calibration.

- You're ignoring beamforming and array effects.

Imho irrelevant. Goal of beamforming is to present outer sound as true as possible. If it can pick gains in background noises, it should pick drops in it too.

- You're mostly ignoring multipath effects around the occluder.

I do ignore bottom and surface reflection. I can run the simulation with them, but again, it does not look much different. Other multipaths should not matter at 130m.

- Your sim treats the kilo as a perfect occluder with no transparency.

Now that is interesting problem. The hull of the sub could transfer some of the sound, and it is out of reach of my simulation. Anyway at least all reflected sound wont be passed through. And we know that subs without coating reflect sound rather well. So it cannot pass it well at the same time.
Kilo has rubber coating though (I believe). It would work by absorbing, not passing through (I believe). I guess it's mostly aimed against high frequency active sonar, but it could also work at 150Hz range, also for masking sounds coming from inside the sub.

- Your sim assumes noise sources occluded by the kilo behave with strong directional correlation. This is not the case in ambient sea noise.

At 150Hz the background noise should be rather directional in horizontal plane. I could not find much about coherence, but since it can be said that it is directional, it also must be rather coherent.

- Ray based models don't simulate low frequencies properly at all, especially at your 150 Hz test case. Sound doesn't behave like a ray at low frequencies, it behaves more akin to electrons in a waveguide, with "fuzziness" and a distinct lack of directionality.

This is not ray model. It's completely wave based simulation. It should simulate diffraction and interference. You can see the shadow has rather fuzzy edges, and it is filled with energy over distance. That is the diffraction in work. It's just not that strong, so it could erase any disturbance left by the object.

- The "kilos are a black hole in the ocean" thing is a myth, started by a nefarious source linked in a wikipedia article.

Have the link ?

Btw. you really seem to know a lot .. what's your relation to underwater sound ?