Acoustic velocity measurements in seafloor sands at frequencies from 1 to 400 kHz

Abstract

We measured the acoustic velocity and attenuation at frequencies from 1 kHz to 400 kHz in shallow seafloor sands off Fort Walton Beach, FL, USA. We used three separate systems with overlapping frequency ranges in order to cover this entire frequency range. For frequencies from 1 to 20 kHz, we implanted a seafloor array of 35 hydrophones and 5 three-component accelerometers at depths from 0 to 1 m over a 4 m by 4 m area, and recorded signals from two acoustic sources positioned at offsets from 1 m to 20 m. Measurements from 15 to 120 kHz were made at 30-cm sediment depths with the In Situ Sediment Acoustic Measurement System (ISSAMS), which consists of a linear array of 4 piezoelectric probes; the outer probes transmit a single-frequency burst while the inner probes act as receivers. Additionally, velocity measurements were made on diver-collected cores (5–20 cm sediment depths) at frequencies from 50 to 400 kHz. We present comparisons of the measured frequency dependence of the acoustic velocity and attenuation to theoretical predictions from various constitutive and wave propagation models, parameterized with inputs from detailed characterizations of diver-collected cores.