Acoustical characterization of a seagrass meadow in the Lower Laguna Madre

Abstract

This talk presents preliminary results from an experiment conducted in the Lower Laguna Madre, Texas to characterize the physical and acoustical properties in a meadow of Thalassia testudinum. Concurrent measurements were collected using (1) acoustic probes, (2) side-scan and parametric sonar, (3) broadband propagation, and (4) sediment cores. The acoustic probes provided localized, direct measurements of sound propagation in the seagrass canopy as well as geoacoustic properties (compressional and shear wave speed and attenuation) of the seagrass-bearing sediment. The side-scan and parametric sonars were used to survey for seagrass abundance and sub-bottom layering. Broadband signals produced by a combustive sound source were recorded at several ranges by hydrophones and geophones and were used to infer geoacoustic properties of the seagrass and underlying sediment for rapid environmental assessment. The sediment cores were analyzed in the laboratory using both low-frequency resonator measurements and high frequency travel-time measurements to estimate compressional wave speed, after which they were sectioned and measurements of sediment grain size, porosity, and biomass were obtained. The combination of these data sets provides a unique characterization of the geoacoustic properties of a seagrass meadow. [Work sponsored by ARL:UT IR&D and ONR.]