Observations of Sediment Attenuation from the SBP 29

The R/N Sally Ride conducted acoustic experiments between Alameda and San Diego, California, USA during mission SR2104 in June and July of 2021. One of the acoustic instruments was the Kongsberg SBP 29, a sub-bottom profiler that operates in the 2 to 9 kHz frequency range. The SBP 29 was designed to have significant acoustic penetration into the seafloor and can provide useful physical acoustics information related to sediment layering and properties. In this work the spectral ratio method is used to estimate attenuation within the sediment and infer the mean sediment grain size and dominant sediment type. The method allows for sediment attenuation estimates of a single depth window or depth-dependent estimates calculated from multiple windows. Results are presented geospatially at two test sites and good agreement is found with core sample data. Variability and limitations of the spectral ratio method are also discussed.