Thread: Sonar Quiz #36

Explain what causes "multi-bottom echoes" ...



Why do we never see "multi-bottom echoes" in SI ... ??



pic credits to Wayne and Doug

Rickie

Multiple bottom returns are created from the sound energy bouncing back and forth between the bottom and surface of water and normally only occurs with harder bottoms. In 2D, the stronger portion of the beam is directed downward. In Side Imaging, the stronger portion of the beam is directed outward and not likely to produce multiple returns.

As a note, if you look at the left side water column in SI you can see what happens with sound reflections from the transducer probably being mounted on the right side of a jack plate and sound bouncing back from the left side of the jack plate.

You can correct it by reducing the 2D sensitivity or by adjusting the max depth setting.

EZ and BobB seem to have this sewed up!

Originally Posted by Redge

EZ and BobB seem to have this sewed up!

I'd say "sewed up" is correct ...

Very good guys ...

Rickie

I was told the thw sonar is shooting threw the soft mud then it hits a hard bottom.

I hope I am not too blunt, but that isn't the way it works ...... sonar will not reflect off a deep layer of hard bottom thru a soft bottom. When you get multiple returns, it is usually because you have a hard bottom, not a soft bottom.

Originally Posted by BobB

I hope I am not too blunt, but that isn't the way it works ...... sonar will not reflect off a deep layer of hard bottom thru a soft bottom. When you get multiple returns, it is usually because you have a hard bottom, not a soft bottom.

Your not being to blunt IMHO. Just trying to learn, I had heard the same thing about shooting thru mud /silt to a hard rock. So sonar doesn't really do that? Just trying to learn and I definitely don't know the answer.

Originally Posted by frontierman

I was told the thw sonar is shooting threw the soft mud then it hits a hard bottom.

Originally Posted by Redge

I had heard the same thing about shooting thru mud /silt to a hard rock. So sonar doesn't really do that?

Maybe this is what some have referred to (and then mis-interpreted just a little) ...

From page 20 in the 1197 Operations Manual ...:



Rickie

The first tip off to a double echo due to hard bottom is that the second echo will be exactly twice the first bottom echo.... if there is a third, it will be triple.