Side scan sonar acoustic variability

The authors report the results of research on the inherent variability of side-scan sonar imagery to determine the magnitude and nature of image intensity fluctuations. Two experiments are presented in which a Klein 100-kHz system is operated under controlled conditions that remove all but purely instrumental and acoustic causes of image variability. The result of one experiment in a test tank is a statistical analysis of the transmitted waveform. A second experiment, conducted from the Woods Hole Oceanographic Institution Pier, allows similar analysis for the combined side-scan sonar transmit/receive signal path. Significant fluctuation in side-scan sonar acoustics and in the images obtained was found. The lack of temporal or spatial correlation of the observed fluctuation shows that they are not due primarily to transmitter power fluctuations. In the absence of influences such as towfish instability or changes in imaging geometry, fluctuations of up to 14% were observed for images of identical bottom features. The fluctuations are approximately Gaussian distributed and nearly a constant percentage of mean intensity, indicating that this is a multiplicative rather than additive effect