High-Frequency Broadband Seafloor Backscatter in a Sandy Estuarine Environment
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 discrete particles (e.g., shell hash) are likely contributors. To further our understanding of the impact these mechanisms have on seafloor scattering, broadband (100-250 kHz) acoustic measurements were taken at a grazing angle of 45° in a shallow-water, sandy environment with a known presence of shell hash. Stereo imagery was collected simultaneously to quantify the surficial roughness of the seafloor. Sediment samples were also collected at the site of the experiment to quantitatively analyze the content of shell hash. Backscatter observations between the frequencies of 170 kHz – 250 kHz showed a minimal increase in amplitude with increasing frequency while observations at lower frequencies between 100 kHz – 150 kHz showed an apparent increase in amplitude relative to increasing frequency. Data to model comparisons of the frequency dependence of seafloor backscatter were made to both roughness and discrete particle scattering models indicating neither model is a good descriptor of the seafloor backscatter response.