Foote Kenneth G.

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Kenneth G.

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Now showing 1 - 8 of 8
  • 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
    Speed of sound in Euphausia superba
    (Acoustical Society of America, 1990-04) Foote, Kenneth G.
    The speed of longitudinal sound waves in Antarctic krill has been measured by the time‐of‐flight method. The result of 17 separate measurement series on different assemblages of living krill is that the animal’s sound speed exceeds that of seawater at the same temperature by 2.79±0.24%. The mean lengths vary from 29.4 to 38.9 mm, with overall mean 32.2 and s.d. 2.5 mm. The corresponding density of krill of mean length 31 mm is 1.0647±0.0069 g/cm3 . Measurement temperatures varied from 5.3 to 12.1°C; corresponding salinities varied from 32.5 to 33.87 ppt, which also represent the ambient state. The ambient sea temperature was 2.0±0.3°C.
  • Article
    Correcting acoustic measurements of scatterer density for extinction
    (Acoustical Society of America, 1990-09) Foote, Kenneth G.
    Extinction is sometimes a major problem in acoustic surveys of fish stocks, as it often occurs when the fish are concentrated and easiest to survey. The same may be true of certain macrozooplankton, such as krill in swarms. This study aims to describe how to correct single‐ping measurements of the vertical distribution of scatterer density for extinction. The general case is considered in which the aggregation density is variable and the mean backscattering and extinction cross sections vary with depth. By dividing the water column into a finite number of layers, with constant properties within each, a closed‐form mean‐field solution is derived. Methods of applying this to single‐ping echo records and the quality of the solution are both examined. Extinction is discussed vis‐à‐vis multiple scattering. Application of the technique in other areas, e.g., in remote probing of the atmosphere by lidar, is mentioned.
  • Article
    Acoustic sampling volume
    (Acoustical Society of America, 1991-08) Foote, Kenneth G.
    Knowledge of the acoustic sampling volume is necessary in many quantitative applications of acoustics. In general, the sampling volume is not merely a characteristic of the transmitting and receiving transducers, but also depends on the concentration and scattering properties of the target, the kind of signal processing performed on the echo, and the detection threshold. These dependences are stated explicitly in formulas for the sampling volume and a differential measure, the effective equivalent beam angle. Numerical examples are given for dispersed or dense concentrations of both point scatterers and directional fish scatterers. Application of theory to optical and other remote sensing techniques is mentioned.
  • Article
    Target strengths of Antarctic krill (Euphausia superba) at 38 and 120 kHz
    (Acoustical Society of America, 1990-01) Foote, Kenneth G. ; Everson, Inigo ; Watkins, Jonathan L. ; Bone, Douglas G.
    Encaged aggregations of live krill in good to pristine condition have been ensonified at 38 and 120 kHz. Concurrent underwater television observations of behavior resemble those made by underwater divers in naturally occurring swarms, with comparably high densities of the order of 104 animals/m3 . Mean, single‐animal target strengths have been inferred from measurements of echo energy. For aggregations with mean lengths in the range [30,39] mm, the mean single‐krill target strengths are in the range [−88,−83] dB at 38 kHz and [−81,−74] dB at 120 kHz. Collateral measurements on some of the same encaged specimens determined a density contrast of 1.0357±0.0067 and sound‐speed contrast of 1.0279±0.0024, relative to seawater. These numbers have been used with the fluid‐sphere model as stated by Greenlaw [Limnol. Oceanogr. 24, 226–242 (1979)] . Computed backscattering cross sections have been averaged over the length distributions of each measured aggregation, resulting in target strength predictions in the range [−86,−80] dB at 38 kHz and [−79,−76] dB at 120 kHz.
  • 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.
  • Article
    Postprocessing system for echo sounder data
    (Acoustical Society of America, 1991-07) Foote, Kenneth G. ; Knudsen, Hans Petter ; Korneliussen, Rolf J. ; Nordbø, Per Erik ; Røang, Kjell
    Echo sounding is a powerful and widely used technique for remote sensing of the marine environment. In order to enhance the power of the echo sounder, a postprocessing system has been designed and realized in standard software that is essentially machine independent. This has been done by adhering to the following international standards: UNIX operating system, C programming language, X Window Systems, Structured‐Query Language (SQL) for communication with a relational database, and Transport Control Protocol/Internet Protocol (TCP/IP). Preprocessed data are transferred from the echo sounder to the postprocessing system by means of a local‐area network (LAN), namely Ethernet. Development of the postprocessing system, for analysis of such diverse scatterers as plankton, pelagic, and bottom fish, and the bottom itself, is documented in the following way. The history of echo integration is summarized. User requirements for the new system are listed. Reasons are given for the choice of the particular computing environment, including both hardware, software, and external communications. The system design, consisting of data flow and graphical user interfaces, is described. Implementation of the system is defined through integration techniques and a discussion of performance issues. Operating procedures and the first field trials of the system are described. Several features characteristic of and perhaps unique to the postprocessing system are, for example: (1) user definition of arbitrarily shaped integration regions, including non‐constant‐depth intervals, by means of interactive graphics; (2) preprocessor error correction, e.g., adjustment of the noise threshold or redefinition of the detected bottom; (3) use of several color map techniques in order to extract such information as signal strength and shape; and (4) the scheme of interconnections of graphical user interfaces, database, and data files. This work does not introduce a set of computer instructions. It does describe a design philosophy and method of realization that may have broader applications in acoustics than that ostensibly concerned only with the quantitative estimation of fish abundance.