UACE2025: Direct measurements of the geoacoustic properties of seagrass bearing sediments

• Session:
  Acoustic modelling and Inversion methods
• Paper:
  Direct measurements of the geoacoustic properties of seagrass bearing sediments
• Author(s):
  Kevin M. Lee, Megan S. Ballard, Andrew R. Mcneese, Preston S. Wilson
• Abstract:
  Biological processes and physical characteristics associated with seagrass can greatly affect acoustic propagation in coastal regions. An important acoustical effect is due to bubble production by the plants, which can have significant impact on both object detection and bottom mapping sonars by increasing clutter through reflection, absorption, and scattering of sound. In addition to photosynthesis-generated bubbles and gas-bearing leaf tissue in the water column, the plant rhizomes also contain aerenchyma (gas-filled channels), which allow for diffusion of oxygen into the surrounding sediment. Whereas previous studies on the acoustic properties of seagrass have focused on sound propagation and backscatter in the water column, little prior work has focused on measurement of acoustic properties below the water-sediment interface where the plant rhizome and root systems exist. To study these effects, in situ acoustic measurements were conducted in a bed of Thalassia testudium in east Corpus Christi Bay, Texas, USA. Direct measurements of sound speed and attenuation were obtained in the water column above the seagrass canopy, inside the seagrass canopy, and at discrete depths within the sediment. A complimentary set of measurements were obtained in a bare sediment region located a few meters away. In addition to standard measurements of geoacoustic properties (sediment density, grain size, etc.), biomass was also estimated from cores collected at each site. Generally, the sediment beneath the seagrass bed had significantly lower wave speed and higher attenuation compared to the bare sediment. Frequency dependence of the sound speed and attenuation in the seagrass bed relative to the bare sediment was also investigated. [Work supported by the ARL:UT IR&D program and ONR.]
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Contact details

• Contact person:
  Dr Kevin M. Lee
• e-mail:
  
• Affiliation:
  Applied Research Lab, The University of Texas at Austin
• Country:
  United States