Low-frequency attenuation and sound-speed measurements in marine sediments using an impulsive source.

Abstract

Low-frequency (200–1000-Hz) sediment attenuation and sound-speed measurements were conducted at a site on the New Jersey Shelf where additional data sets from a chirp-sonar bottom profiler (2–12 kHz) and an acoustic-probe system (10–80 kHz) are available. Impulsive sound signals, generated by automated light-bulb implosions, are received by a 16-element vertical line array at short ranges (<500 m). Precursor arrivals and signals reflected from the R-reflector are used to estimate sediment sound-speed and attenuation. Attenuation in dB/m/kHz is estimated using the spectral-ratio technique and sound-speed is estimated from the travel-time analysis. Frequency dependency of sound-speed and attenuation is also investigated within a wide frequency band (200 Hz–80 kHz) using the results from impulsive source, chirp-sonar, and acoustic-probe measurements. Measured attenuation and sound-speed values seem to be well predicted by an extended Biot theory for sediments with distributed pore sizes. [Work supported by ONR.]