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Figure 19. Image of sidescan-sonar data collected in the National Oceanic and Atmospheric Administration survey H12298 study area.

Figure 20. Detailed image of boulders and mottled areas in sidescan-sonar data.

Sidescan Sonar

Sidescan-sonar data were only collected along the south coast of Fishers Island, within 1 to 2 km of the shore, in order to provide complete coverage of the area when used together with the MBES data (fig. 19). Several patterns are visible in the sidescan-sonar mosaic, including areas of high and low backscatter, high-backscatter targets, and mottled areas. High backscatter (light tones) generally represents areas of coarser grained sediments than those elsewhere in the mosaic and high acoustic reflectivity; low backscatter (dark tones) generally represents areas of relatively fine-grained sediments and low acoustic reflectivity and shadows. Areas of high backscatter are prevalent in the sidescan-sonar mosaic; however, there are several areas of low backscatter in shallow, flat, protected areas near the shore. High-backscatter targets with low-backscatter shadows, representing boulders and their acoustic shadows, are seen in the mosaic (fig. 20). Also visible in the sidescan-sonar data is an area of mottled high and low backscatter off the coast of Fishers Island (fig. 20).