In situ measurements of sediment sound speed and attenuation in the frequency band of 0.5–10 kilohertz

Abstract

Knowledge of sediment sound speed and attenuation is crucial for predicting sound propagation. The sediment Acoustic-speed Measurement System (SAMS) was designed to measure frequency dependence of sound speed and attenuation within the surficial 3 m in the frequency band of 2–50 kHz. SAMS has two independent and interchangeable drill systems: one employs suction and the other a water jet. The suction system has minimal disturbance on the medium around the penetrating probe while the water jet system can help penetrate consolidated shell/sand layers. Depending on sediment types encountered, the two systems can be interchanged on site in less than 4 h. SAMS was successfully deployed during the Shallow Water 2006 experiment on the New Jersey continental shelf. It was also deployed during the Gulf Experiments 2011, 2012, and the Target and Reverberation Experiment 2013, all conducted off Panama City, FL, where sediment types range from mud to coarse sand. Sediment sound speed and attenuation results from the two experiments are presented. In preparation for the upcoming Seabed Characterization Experiment, the effort to extend measurements down to 500–1500 Hz, where dispersion is of particular importance, will be discussed as well. [Work supported by ONR.]