Some questions from a newbie

[Polak2]

but still don't know how to determine where the layer is or how to determine where the shadow zone is.

Look at your last type of the sonar controls - SSP(sound speed profile) . Watch basic sonar tutorial #5 at the end on how to use it.

My question on shadow zone is: can TA of the surface unit be lowered into to shadow zone and if it can, what happens then to the sub protection?