ANALYSIS OF SIDE-SCAN SONAR DATA TO CONSTRAIN GEOLOGIC SETTING OF OFFSHORE WIND ENERGY AREAS

In this study, a procedure for analyzing large-scale side-scan sonar projects was developed. Using a dataset provided by the State of Maryland Energy Administration, side-scan sonar data within the Maryland Wind Energy Area (WEA), encompassing over 320 km², were analyzed to better constrain the area’s seafloor characteristics. The Maryland WEA is one of four Bureau of Ocean Energy Management regions that have been designated for offshore wind development along the Mid-Atlantic Bight portion of the United States eastern continental shelf. Offshore wind projects require a large capital investment. Up to 25% of total project costs can be associated with wind turbine foundations that are directly influenced by seafloor conditions.

After data import into the software package SonarWiz, the analysis procedure included: bottom tracking, identifying and digitizing surficial features including hazards and boundaries between different sediment types, and creating a mosaic base map. To classify bottom sediment types, automated (SonarWiz and ENVI) and manual (user-defined) techniques were employed. The techniques were compared based on accuracy, ease of use, and relative time involved for analysis. The two automated classification methods (SonarWiz and ENVI) produced more consistent results than the user-defined method. The user-defined method was the easiest to use, followed by ENVI, and SonarWiz. The ENVI method required the shortest time for completion, followed by the user-defined method, and SonarWiz. A comparison of the classification results with previous geologic studies indicate that intensities of the side-scan sonar returns can be correlated to first-order fine-, medium-, or coarse-grained sediments.

The procedure developed can be used to analyze large-scale side-scan sonar datasets, like those that are/will be collected in geophysical surveys of offshore WEA’s. When combined with sub-bottom investigations, sediment sampling, and geotechnical measurements, side-scan sonar data can be used to place constraints on the types and distributions of sediments that will be encountered offshore. This information can be used by design engineers and planners to develop the most cost-effective foundations and thus aid in reducing the overall costs associated with offshore wind energy projects.