Blanking

Sonar signal blocking caused by discontinuities in the water resulting in an empty, unprinted area in the sonar data; sometimes, but rarely, caused by local signals or radiation external to the control/display portion of the sonar system. Blanking often occurs when the transducer is towed through another vessel's (or the towing vessel's) wake. Cavitation and air mixing in these cases block the sonar signal. A vessel hull can also cause blanking, if the transducer is towed at very shallow depths.