Measurements and modeling of acoustic propagation in a seagrass meadow

Abstract

This talk presents results from an acoustic propagation experiment conducted in the Lower Laguna Madre to characterize the acoustical properties of a seagrass meadow. At the location of the experiment, the water was one meter deep, and the seabed was covered by a dense growth of Thalassia testudinum, a type of seagrass that grows from a long, jointed rhizome buried 5 cm to 10 cm below the seafloor. The biological processes and physical characteristics associated with seagrass are known to affect acoustic propagation due to bubble production, which results in dispersion, absorption, and scattering of sound. During the experiment, a Combustive Sound Source was used to produce broadband signals at ranges of 20 m to 1000 m from the receiver location. Three sensors were positioned at the receiver location: two hydrophones located within and above the seagrass canopy, and a single-axis geophone. The data were analyzed for the purposes of predicting acoustic propagation in seagrass meadows and for estimating environmental parameters in very shallow, biologically active environments. Additionally, seagrasses are a vital part of the global carbon cycle and this work explores the feasibility of using of acoustic signals to estimate carbon stores. [Work sponsored by ARL:UT IR&D and ONR.]