Use of high-resolution sidescan sonar data to quantitatively map and monitor a mid-continental shelf hardbottom 23-mile site, Onslow Bay, NC

TL;DRAbstract

This study attempts to constrain the spatial and temporal variations in the seafloor morphology, as well as the relationship between sidescan sonar data and seafloor characteristics at the 23-Mile hardbottom area on the mid-continental shelf of Onslow Bay, NC. The 23-Mile site consists of an upper limestone hardbottom at 29-30m water depth covered in a thin discontinuous veneer of sediments. The lower sand flats at 32- 33m depth consist of concentrated areas of contrasting grain size. A dual-frequency sidescan sonar system was used to repeatedly image the seafloor of a 3.5 km by 2.1 km region at 23-mile site over a period of 2.5 years. Cruises were conducted in December 1999, December 2000, July 2001, and May 2002. Textural analysis of the sidescan sonar imagery was conducted using gray-level co-occurrence matrices. Two textural indices: entropy (acoustic roughness), and homogeneity (level of textural organization) were used in conjunction with gray-level to identify seabed types. The

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