Directional characteristics of sidescan images

This paper presents a frequency domain model to quantitatively assess the impact of the direction of the towfish relative to the seabed in the interpretation of sidescan images. This model is extended from a model used for photographic images and thus requires the application of a number of assumptions which are investigated to ensure their validity in this application. The response predicted by the model is then verified using both simulated and real sidescan sonar images. These directional characteristics predicted by the model are important because texture classification schemes used for the interpretation of sonar images commonly employ directional feature measures to discriminate between texture regions in an image. Therefore, the result of the sonar process on an omni-directional texture feature is investigated. Simulations verify that, as predicted by the frequency domain model, the direction of the towfish relative to the seabed has a profound effect on the output of the texture feature. This therefore impacts on the success of any texture based classifier which neglects to consider the directional effects