Multi-angle measurements of high-frequency seafloor acoustic scattering strength at the mouth of the Piscataqua River, Gulf of Maine

Active sonar systems are used for remote sensing applications such as hydrography, seafloor characterization, and target detection. While previous work has focused on the dependence of seafloor scattering strength (SS) on sediment type, grazing angle, and frequency, SS seasonal variability has received less attention. Surface roughness is a key contributor to SS and can be influenced by environmental drivers such as storm-induced hydrodynamics and benthic activity. This study quantifies the temporal variability of SS over weekly to yearly timescales using data from a seabed-based tripod deployed at a sandy site near the mouth of the Piscataqua River (NH, USA). A 2-m-tall tripod equipped with a 70, 200, and 333 kHz transducer and a CTD was deployed on the seabed for three experiments (about 6 months in duration) between 2022 and 2025. Monthly vessel-based split-beam surveys complemented the tripod data. This work focuses on the 70-kHz continuous wave data. Results show that scattering strength varied by up to 10 dB potentially in response to storm activity, with recovery during calmer periods. Another potential contribution to the changes seen in SS scattering strength was from biological activity. These observations provide new insights into environmentally driven variability in seafloor scattering and have implications for acoustic modeling and sonar calibration.