Acoustic bottom scattering is the main source of reverberation background in target detection and recognition near the seafloor. Accurate estimation of bottom scattering strength is necessary for prediction of sonar performance in the presence of reverberation in shallow-water environments. A measurement of bottom backscattering strength at midfrequency in a shallow-water environment of the South Yellow Sea of China was carried out in April 2016, where the water depth was 39 m. The surface of the seafloor was relatively flat and covered by some shell fragments observed through a digital camera system. Core data showed that the main component of sediment at this experiment site was fine sand. The backscattering strength as a function of grazing angle (20°–70°) in the frequency range of 6–12 kHz was extracted from monostatic backscattering data, employing an omni-directional source and an omni-directional hydrophone. The measured backscattering strength increases with the increase of the grazing angle, and changes more rapidly at large grazing angles (60°–70°). Comparing the data at different frequencies, it is found that the measured backscattering strength slightly increases with the increase of the acoustic frequency. A fit of Lambert's law to the measured data shows that the backscattering strength deviates from the Lambert's law at large grazing angles. Finally, the fitted result of a scattering model to the measured data suggests that seafloor roughness scattering is larger than that from sediment volume heterogeneity in the measurement frequency band.

Seabed acoustic backscattering measurements were conducted at a shallow water site in the South Yellow Sea of China. The acoustic backscattering strengths from a fine sand seabed were obtained in a wide range of grazing angles (26°–60°) at 12–24 kHz. Backscattering strengths exhibited frequency and grazing angle dependence, which increases with increasing frequency and grazing angle. The predictions of the scattering model, based on the effective fluid density model, whose input parameters were obtained via measurements or acoustic inversions, were compared with the measured data. The scattering model predictions agreed well with the measured data across all of the investigated frequencies and grazing angles. The comparisons show that rough surface scattering plays the leading role within the 26°–60° grazing angle range at 12 kHz in fine sand sediments. When the frequency exceeds 16 kHz, sediment volume scattering becomes the primary mechanism of seabed acoustic scattering in a broader range of grazing angles as the frequency increases. Moreover, a transition in the scattering mechanism was noted in a specific grazing angle range as the frequency increased from 12 to 16 kHz.