Orientation dependence of the acoustic backscatter for elongated zooplankton
Johnson, Matthew L.
MetadataShow full item record
The width of the main lobe of the acoustic backscatter directivity pattern of decapod shrimp (Palaemonetes vulgaris) is examined versus acoustic frequency. Using the distorted wave Born approximation (DWBA) and the geometry of a prolate spheroid, an analytic formula for the backscatter cross section as a function of orientation angle is derived. A directivity pattern is determined from the analytic formula and the width of the main lobe (beam width) is computed. The relationship between beamwidth and acoustic frequency is presented in plots of beamwidth versus ka and L/λ. The model is adapted to experimental limitations of animal motion, discrete sampling and observed side lobe levels. The backscatter directivity patterns of live decapod shrimp, determined experimentally at frequencies between 72 and 525kHz, are presented. A non-monotonic relationship between beamwidth and frequency is illustrated in this study. This relationship is in contrast to the monotonic relationship exhibited when sound scatters off of an impenetrable flat plate. Reasonable agreement is found between the theoretically predicted beamwidths and most experimental data, where the beamwidth was more-or-less oscillatory about a mean value of 19°. The structure can at least be partly explained by scattering theory.
Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1993
Suggested CitationThesis: Johnson, Matthew L., "Orientation dependence of the acoustic backscatter for elongated zooplankton", 1993-09, DOI:10.1575/1912/5538, https://hdl.handle.net/1912/5538
Showing items related by title, author, creator and subject.
Ogden, Kelly A. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2017-02)Internal hydraulic jumps in flows with upstream shear are investigated numerically and theoretically. The role of upstream shear has not previously been thoroughly investigated, although it is important in many oceanographic ...
Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers Manning, Cara C. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2017-02)In this thesis, I use coastal measurements of dissolved O2 and inert gases to provide insight into the chemical, biological, and physical processes that impact the oceanic cycles of carbon and dissolved gases. Dissolved ...
Coral biomineralization, climate proxies and the sensitivity of coral reefs to CO2-driven climate change DeCarlo, Thomas M. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2017-02)Scleractinian corals extract calcium (Ca2+) and carbonate (CO2−3) ions from seawater to construct their calcium carbonate (CaCO3) skeletons. Key to the coral biomineralization process is the active elevation of the CO2−3 ...