Real-time echosounder based acoustic seabed segmentation with two first echo parameters

Abstract

Seabeds with different physical and biological properties (for example, mud, sand, gravel, rock, seagrass, shell beds) generally produce differently shaped echoes in response to echosounder pings. After allowance for propagation losses and for artefacts caused by sampling at equal time intervals, instead of equi-angular spacing, geometrical (i.e. shape based) estimates of the similarity of echo envelopes may be used to geographically segment the seabed into areas with similar acoustic responses. Post-processing of entire echoes by direct clustering provides a statistically and geometrically optimal method of segmentation which in itself does not need ground truthing, since it is based on the actual seabed acoustic response. However, real-time processing allows sampling strategies to be adapted in response to findings during survey. A real-time segmentation method is presented which uses only two simple echo parameters. Classes formed by direct clustering of actual echoes map to unique areas of the 2-parameter space in a very simple and regular fashion, fully validating its use as a segmentation scheme. Groundtruth (seabed samples or video) must be taken if descriptions (labels) are to be assigned to the 2-parameter segmentations (the segmentation becomes a classification). However, the relation to direct clustering results means that in principle groundtruth is not needed to validate the segmentations. In contrast it has never been shown that echo features used by existing real-time schemes contain sufficient information to adequately characterize seabeds.