High-frequency broadband seafloor backscatter in a sandy estuarine environment

Abstract

Seafloor backscatter collected with high-frequency (>100 kHz) hydrographic echosounders has become an important aspect of seafloor characterization for benthic ecologists and other scientists. The mechanisms that control acoustic scattering at these high frequencies are not completely understood, although surficial roughness and the presence of large scatterers (e.g., shell hash) are likely contributors. To further our understanding of these mechanisms, broadband (100–250 kHz) acoustic measurements were taken at a grazing angle of 45 degrees in a shallow-water, sandy environment with a known presence of shell hash. Stereo imagery was collected simultaneously to quantify the roughness spectrum of the seafloor. Sediment samples were also collected on site of the experiment to quantitatively analyze the content of shell hash. The frequency dependence of the seafloor backscatter will be discussed in terms of its consistency, or lack thereof, with surficial roughness and shell-fragment scattering models.