Estimating Surficial Seafloor Sediment Mud Fraction Using Empirical Orthogonal Functions of Acoustic Backscatter Waveform Properties

Abstract:

Seafloor classification and environmental assessment in shallow marine waters are crucial to habitat mapping, coastal management policies and maintaining navigational waterways. Unfortunately, many current assessment techniques using remote acoustic methods have had limited success in shallow waters, often leading to sparse quantifiable data to support marine policy decisions. This problem is exacerbated by the highly variable bottom composition of typical coastal and estuarine environments. In this work, field observations from an Odom Echotrac vertical-incidence echosounder with a dual-frequency (24 and 200 khz) transducer were used to estimate seafloor sediment characteristics in regions with variable bottom types. Observations were obtained in water depths ranging 0.5-24 m of the Little Bay, NH, during February and March, 2013. Comparison between backscatter waveform properties and sediment grain size distributions show varied degrees of predictive capability. In an effort to better capture the collective effects of seafloor sediment's composition on acoustic returns, empirical orthogonal functions (EOF’s) were computed from waveform properties and compared with observed mud-sand fractions and bulk density measurements. Results from this analysis will be presented and discussed. This empirical analysis provides an objective means to interpret acoustic backscatter, an important step towards a widespread quantitative assessment of shallow water seafloor sediments. This work was supported by NOAA, New Hampshire Department of Environmental Services, and ONR.