Thread: Sonar Quiz #25

I think it is possible that the fish could have been in the outer fringes of the DI fan beam and be somewhat missed by the 2d cone ...

However...this example would tend to follow the explaination from Airmar ... (the notable aspect being the sharp rise in the bottom) ...

From Airmar ...
http://www.airmartechnology.com/uplo...Operations.pdf

What is target masking?

There are areas within the transducer's range which seem to be invisible to the echosounder. This is know as target masking. It can happen if the lake or sea bottom drops off suddenly or contains a large rock. The sound waves will bounce off all of the sea bottom within the sound beam and return as strong echoes. The echoes from the highest point, the rock or dropoff, return to the transducer first, falsely indicating the apparent depth of the bottom. Small fish below the highest point will produce relatively small echoes which will return after the larger ones. Therefore, fish can be swimming around the sides of a large rock or a dropoff, be in the sound field, and yet remain invisible to the echosounder.



Rickie