Construction of seafloor thematic maps from multibeam acoustic backscatter angular response data

An automatic approach for delineation of areas representing different acoustic facies is presented. A backscatter mosaic (a gray-scale image) is oversegmented, honoring all possible boundaries, both real and false (acquisition and construction artifacts), in order to separate relatively homogeneous and contiguous groups of pixels of the mosaic, which are called segments. The size of the segments is chosen such that each one is considered to represent a single acoustic facies. These segments are then joined together to end up with a predefined number of “acoustic themes,” in a process called coalescence. The difference between “facies” and “theme” is that the former represents an abstract type of seafloor, and the latter, an area (or areas) selected manually or automatically with common seafloor properties. Ideally, one theme would correspond to a single facies. Themes that are used for assignment to segments are chosen prior to coalescence, either manually or by one of the three automatic methods proposed in the paper. The process of coalescence of segments is based on all acoustic data associated with each segment (not just data used for mosaic construction), their proximity and shape. Results of segmentation are unbiased but depend on a specific goal that the user is trying to achieve.