Measurements and Modelling of Shallow Water Reverberation

Active sonar is a useful tool for monitoring the water column and for detecting foreign objects therein. The performance of the active sonar can be improved with a suitable choice of signal waveform. The waveform should be adapted to the targets to produce a high echo level, and it should also be designed to minimise the reverberation level. In this way the signal-to-noise ratio, the echo level compared to the reverberation level, is optimised. In this report we focus on how to suppress reverberation with the choice of the active sonar waveform. We report on a field experiment that was conducted in the southern part of the Stockholm Archipelago. Reverberation levels were recorded using a set of diffierent signal waveforms. Theoretical predictions are confirmed, for example, large bandwidth signals produce significantly less reverberation than narrowband signals. A theoretical reverberation model has been developed, called SLOPERVI3. It can be used to model monostatic reverberation from a bottom with range dependent depth. We present comparisons of our expe- rimental data to SLOPERVB results. The agreement is satisfactory up to distances of 200-250 m from the sound source. At longer distances, the reverberation level from the model is below the noise level of the experiment.