For example, an increase in noise levels in and around the sonar transducers as a result of radiated noise from the host ship is one common type of interference. Typically sonar transducers are installed in the bow of a ship, well away from the engineering spaces and heavy machinery, to reduce the chances of interference problems. However sometimes the best attempts during installation to prevent radiated noise interference fail, resulting in a particularly poor performing sonar. After installation, these problems tend to be systematic and are not easily fixed.

Also common are the occasional sound shorts that radiate noise into the water column and result in poor sonar performance. These occur from improper installation of new pumps or motors, poor maintenance of devices designed to acoustically isolate pumps and other machinery from the hull, or improper stowage of gear around pumps and motors.

While research ships occasionally undergo radiated noise acoustic measurements which might identify sound shorts, they are not common. More frequently the sonar will begin to produce poor, noisy data with little or no warning. While interference of this type may affect a handful of transducers, it is important to remember that the effect won't be seen in a corresponding number of beams. Each transducer contributes to each and every beam. Therefore the increased noise levels will be seen across the entire swath. (Or in the case of a split Port/Stbd array, maybe across half the swath.) In troubleshooting these kinds of symptoms, frequently the last thing considered is an interview of the ship's Captain, First Mate and Engineer for newly installed equipment or other changes that might cause the problem. However it should not be forgotten.

Turbulent flow in the boundary layer around the hydrophone(s) can result in flow noise that can cause acoustic interference. Careful attention to detail at the design and installation can reduce flow noise.There is a good discussion of flow noise in Chapter 11 of Urick[1983].

Bubbles originating at the sea surface and drawn under the hull along flow lines and bubbles that result from cavitation separation are a common problem. Bubbles generate noise which can cause reception problems and they absorb acoustic energy which can cause problems on both transmit and receive.

The effects of bubble sweep down can be reduced by careful attention to detail in the design of transducer installation location and in by minimizing sharp edges and projections that can can result in separation.

One other form of interference that is worth mentioning, is cross talk. Cross talk occurs in sonars with separate port and starboard transducer arrays and is the effect seen when signal and returns produced from one side are inadvertently detected on the other. Considerable design and thought goes into preventing this, yet, under certain configurations it can still occur. Typically the effect is seen in beams near nadir.