Abstract
The Seabed Characterization Experiment was carried out from March 5 to April 10, 2017 (SBCEX17) on the New England Mud Patch, approximately 90 km south of Martha's Vineyard. The SBCEX17 experimental site covers an area of 11 km × 30 km with water depth in the range of 75–80 m. The Sediment Acoustic-speed Measurement System (SAMS) is designed to measure sediment sound speed and attenuation simultaneously over the surficial 3 m of sediments. During SBCEX17, SAMS was successfully deployed at 18 sites, which were chosen to coincide with coring locations, with the goal of developing a geoacoustic model for the study area. In this article, a summary of SAMS operation during SBCEX17 is presented, as well as preliminary results for sediment sound speed and its spatial variation in the frequency band of 2–10 kHz. It is found that in mud, the sound-speed ratio is in the range of 0.98–1. Little dispersion was observed in this frequency band. Using the preliminary SAMS sound-speed results measured at different depths, the sound-speed gradient in mud within the surficial 3 m favors an exponential rather than a linear dependence at SBCEX17 site. Large gradients are observed for depth shallower than 1.5 m. For the sandy basement beneath the mud layer, the sound-speed ratio is as high as 1.105.
Highlights
S EDIMENT geoacoustic properties, which are the most important parameters for predicting sound propagation and reverberation in many cases, are difficult to acquire directly, especially in the lowto midfrequency band
Extensive in situ measurements of sediment properties have been conducted for the ocean acoustics community in sandy sediments and the majority are closely related to major sediment acoustics field experiments sponsored by the U.S Office of Naval Research, Arlington, VA, USA
speed Measurement System (SAMS) was successfully deployed at a total of 18 sites, which were chosen to coincide with the coring locations
Summary
S EDIMENT geoacoustic properties, which are the most important parameters for predicting sound propagation and reverberation in many cases, are difficult to acquire directly, especially in the lowto midfrequency band. In addition to work related to major field trials, descriptions of in situ measurement efforts can be found in [23]–[25] These measurements were conducted from a few hundred hertz to a few hundred kilohertz to study the frequency dependencies of sediment sound speed and attenuation. With limited understanding and measurement of the geoacoustic properties in mud, sediment acoustic modeling is currently an ongoing research topic [34]. During SBCEX17, in situ measurements of sediment sound speed and attenuation in the experimental area were carried out in the frequency band of 600 Hz–10 kHz, using the Sediment Acoustic-speed Measurement System (SAMS).
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