TOWARD REMOTE SEA-FLOOR CLASSIFICATION USING THE ANGULAR RESPONSE OF ACOUSTIC BACKSCATTERING - A CASE-STUDY FROM MULTIPLE OVERLAPPING GLORIA DATA

While the average seafloor backscatter strength within a narrow range of grazing angles can be used as a firstorder classification tool, thi s technique often fails to distinguish seafloors of known differing ge ological character. In order to resolve such ambiguities, it is necess ary to examine the variation in backscatter strength as a function of grazing angle. For this purpose, a series of multiply overlapping GLOR IA sidescan sonar images (6.5 kHz) have been obtained in water depths ranging from 1000 to 2500 m. To constrain the placement of acoustic ba ckscatter measurements and to measure the true impinging angle of the incident wave, the corresponding seafloor was simultaneously surveyed using the Seabeam multibeam system. As a result of the multiple overla p, the angular response of seafloor backscatter strength may be derive d for regions much smaller than the swath width. By using the derived angular response of seafloor backscatter strength in regions for which sediment samples exist, an empirical seafloor classification scheme i s proposed based on the shape, variance, and magnitude of the angular response. Because of the observed variability in the shape of the angu lar response with differing seafloor types, routine normalization of s ingle-pass swath data to an equivalent single grazing angle image cann ot be achieved. As a result, for the case of single-pass surveys, conf ident seafloor classification may only be possible for regions approac hing the scale of the swath width.