[Deamon]

Originally Posted by SeaQueen

You're right. The difference between a bottom bounce and bottom reverberation is that bottom bounce is sound you want and bottom reverberation is sound you don't, basically.

Originally Posted by compressioncut

Bottom reverberation is not volume reverberation. Bottom mostly causes absorbtion and scattering losses, but volume reverb concerns us most.

I think what i'm reffering to is best described as an resonance from a hard bottom or the surface when you are close to it. That was the point of my post. What i'm looking for is a formula that i can utilize in my sonar engine. I hoped to hear the sonalysts guy on how they made it.

This was simulated in sub command when you have approached the surface pretty close. I just did a test: Walked towards a wall and said loud and continuously AAAAAAAAAAAAAAAAAA when approaching the wall very close i notice a significant increase in valume!

Same happens when you approach the surface or hard bottom with a sub that emmits enough noise.

Now i need a formula to calculate this.

Technically, though, usually people refer to reverberation when they're talking about active sonar. There's things called sonar equations, and the reverberation level in an active sonar equation refers to energy from the ping scattered back to the receiver off of any random stuff that's not a target. Essentially, it's just "noise."

In passive sonar, if that actually was an effect, it probably isn't a big deal in most situations. It's reverberation in a looser sense of the term. It shouldn't really be a big deal in most situations, though.

Are you talking about reverberation or the resonance effect that i have mentioned ?

They're just objects with a density other than that of water. That causes some energy to be reflected back. If there's an awful lot of these little objects out there, the effect adds up and you have to account for it.

And the distribution of junk is uneven, what makes the uneven propagation/return right ?

On a side note: In summer when the water becomes warm a curtain liquide chemical transforms in to gas and provides alot of junk. The reverberation increases dramaticaly and virtualy reduces the detection range by half as compared to winter!

My favorite volume scatterers are schools of fish. Their swim bladders are extremely efficient scatterers of sound. You can see them come out at night, and go to sleep during the day. It's kind of neat. There was a neat article in the most recent issue of Physics Today about that actually. It made me happy.

That is good to know. Any explicite data on the return ?

Because the wavelength of the sound is a lot larger than the features responsible for most of the backscattering (mostly waves from the surface and the irregularity of the bottom). There almost certainly is some, but I'm not sure there's enough to worry about most of the time.

But aren't waves longitudinat ? and thus what does the frequency matter then ?

Deamon