Interpretation of the Surficial Geology in the Pulley Ridge Study Area (PULLEY_INTERP.SHP)

The Interp attribute definitions are as follows: terraces: Alternating linear bands of high and low backscatter on the sidescan-sonar imagery. The high-backscatter stripes are interpreted to be reflections off rock surfaces while the low-backscatter stripes are either shadows cast by the terraces or areas where fine-grained sediment has covered parts of the terraces. The bathymetry shows that the terraces occur along the flanks of the narrow ridge that marks the crest of the ridge. Video observations show outcrops of hardgrounds in these areas. high-backscatter: The sidescan-sonar images were smoothed in PCI with a 7x7 average filter, and the areas with values mostly between 117 and 225 were mapped as areas of high backscatter. video observations indicate that these areas are a mix of exposed hardgrounds, carbonate rubble, and deep-water coral. broad lines: The sidescan sonar image shows subtle variations in backscatter intensity that coincide with low-relief ridges on the multibeam bathymetry. depression-large: Sub-circular depressions show on the multibeam bathymetry that have 30-200 m diameters and are less than 3 m deeper than the surrounding seafloor. Many of these depressions have low-backscatter floors on the sidescan-sonar imagery. Video observations indicate that the floors of these depressions are fine sand. mottled-mod: The sidescan-sonar image shows a mottled seafloor of moderate and low-backscatter patches that have dimensions of 50-200 m. The average backscatter values on the filtered image for these areas are mostly 110-120. mod-backscatter: More uniform in backscatter intensity than the mottled-moderate backscatter regions. These areas occur mostly around the edges of the ridge where the seafloor is smoother than it is on the ridge itself. Video observations from these areas show a sandy seafloor with some carbonate cobbles, but the cobbles are not as concentrated as they are on the ridge. mottled-low: Low backscatter areas that are interrupted by sub-circular moderate backscatter patches that are 20-100 m in diameter. The moderate backscatter patches commonly have a pit or mound near their centers. The background in these areas mostly has a DN value less than 100. The multibeam bathymetry shows that the seafloor in these areas is smooth, and video observations indicate that the seafloor is somewhat sandier than other parts of the study area. low-backscatter: Areas with a smooth seafloor with a low-backscatter (DN less than 105) appearance. the only part of the study area with this appearance is in the southernmost part of the area beyond the shelf on the uppermost slope.