Noise and interference
Acoustic noise and bubble interference can affect the quality of the sonar view image.
It is usually easy to recognize interference from other acoustic sources such as echo sounders, pingers, and other sonars. These sources all produce pulses at regularly timed intervals and will therefore tend to create a regular or symmetrical pattern of blips on the screen. Mechanical noise sources such as propellers, hydraulic pumps, and thrusters, are usually more directional and tend to show up only when the sonar is pointed directly at them.
In addition, sonar signals are easily blocked by air or gas bubbles in the water or on the transducer face. As an example, the aeration present in the wake of a vessel will often last for ten to twenty minutes and effectively mask out most sonar returns on the far side. The aeration partially blocks the outgoing pulses as well as any returns. Another source of gas bubbles can be found when a sea bottom containing decomposing organic matter is disturbed by dredging or ploughing.