How useful is bathymetric information in the classification of high frequency sonar surveys?

In several sonar studies, bathymetric information; is used for the correction of amplitude data and the calculation of backscattering strength, which is plotted versus grazing angle and used for seabed classification. Bathymetric data is also used as an easily viewed backdrop to visualize backscattered sonar data in surveys. This work proposes an automatic method that combines amplitude features (describing backscattering strength and sonar texture) with bathymetric features (indicating seafloor variability) for sonar classification. Features are selected per window (of user defined size) and areas around grab samples in a survey are used for training. The importance of bathymetric features is investigated in this study, and highlighted by feature selection algorithms as well as by scatter plots exploring the training areas. Classification rates are significantly improved when both amplitude and bathymetry features are used. The final results show the classified windows plotted versus their exact position in the survey. The method described in this work is applied to a sidescan bathymetric sonar dataset taken in Hopvagen Bay Norway. The methods are also applicable to other sonars which provide bathymetric information; a multibeam sonar is such an example.