Foote Kenneth G.

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Kenneth G.

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Now showing 1 - 5 of 5
  • Article
    Further analysis of target strength measurements of Antarctic krill at 38 and 120 kHz : comparison with deformed cylinder model and inference of orientation distribution
    (Acoustical Society of America, 1993-05) Chu, Dezhang ; Foote, Kenneth G. ; Stanton, Timothy K.
    Data collected during the krill target strength experiment [J. Acoust. Soc. Am. 87, 16–24 (1990)] are examined in the light of a recent zooplankton scattering model where the elongated animals are modeled as deformed finite cylinders [J. Acoust. Soc. Am. 86, 691–705 (1989)]. Exercise of the model under assumption of an orientation distribution allows absolute predictions of target strength to be made at each frequency. By requiring that the difference between predicted and measured target strengths be a minimum in a least-squares sense, it is possible to infer the orientation distribution. This useful biological quantity was not obtainable in the previous analysis which involved the sphere scattering model.
  • Article
    Optimizing copper spheres for precision calibration of hydroacoustic equipment
    (Acoustical Society of America, 1982-03) Foote, Kenneth G.
    An operational definition of backscattering cross section is developed for the wideband reception of finite echoes. This is supported by relative measurements on a set of copper spheres by each of four echo sounders operating at frequencies from 38 to 120 kHz. Experiential and theoretical arguments are advanced for the superiority of commercial, electrical–grade copper in the application. An optimization problem for determining the sphere size is then formulated, and solved for the case of calibration of a 38 kHz echo sounder by a sphere of the described material. The solution: that the copper sphere diameter be 60.00 mm, is tested through a variety of measurements. These demonstrate an accuracy of 0.1 dB. The further exercise of theory indicates the feasibility of precision calibration of diverse hydroacoustic equipment by copper spheres over most of the kilohertz frequency range.
  • Article
    Rather‐high‐frequency sound scattering by swimbladdered fish
    (Acoustical Society of America, 1985-08) Foote, Kenneth G.
    A new model describes acoustic scattering by swimbladdered fish of lengths from at least 8 to 36 wavelengths. It represents a fish by an ideal pressure‐release surface having the exact size and shape as the swimbladder. The backscattering cross section, or target strength, is computed by means of the Kirchhoff approximation. To test the model, predictions of target strengths based on swimbladder morphometries of 15 gadoids of lengths from 31.5 to 44.5 cm are compared with conventional target strength measurements on the same, surface‐adapted fish, anesthetized before acoustic measurement, and shock‐frozen immediately afterwards. Details are given of the swimbladder morphometry. In essence, this consists of slicing the frozen fish with a microtome, photographing the exposed swimbladder cross sections, digitizing the contours, and triangulating the surface between pairs of contours on adjacent, parallel planes. Theory and experiment are compared through the dorsal and ventral aspect target strength functions, their averages, and simulated probability density functions.
  • Article
    Coincidence echo statistics
    (Acoustical Society of America, 1996-01) Foote, Kenneth G.
    Two scatterers at similar range give an echo which may appear to be due to a single scatterer. Methods for determining target strength that depend on resolving single scatterers may fail in this instance. Statistics associated with the described special case of coincidence are derived and illustrated by theoretical computation for the SIMRAD EK500 echo sounder system with the ES38B split‐beam transducer resonant at 38 kHz. Connections to angle measurement in radar and swath bathymetry and to bottom‐scattering‐strength measurement are noted.
  • Article
    Determining the extinction cross section of aggregating fish
    (Acoustical Society of America, 1992-04) Foote, Kenneth G. ; Ona, Egil ; Toresen, Reidar
    When fish are aggregated over a flat bottom, and fish and bottom echoes can be distinguished, it is possible to determine the fish extinction cross section by a simple application of the echo integration method. The theory for this is developed. Measurements at 38 kHz are presented for aggregations of the same 1983‐year class of herring over flat‐bottomed fjord areas in 1988, 1990, and 1991. The ratio of extinction and backscattering cross sections is found to lie in the approximate range from 1.2–2.3, depending on fish size and time of day.