Application of three sound scattering models to threadfin shad ( Dorosoma petenense )

Abstract

Three sound scattering models [T. K. Stanton, J. Acoust. Soc. Am. 86, 691–705 (1989), C. S. Clay, J. Acoust. Soc. Am. 89, 2168–2179 (1991), and C. S. Clay and J. Horne, J. Acoust. Soc. Am. 96, 1661–1668 (1994)] were used to model backscatter measurements from individual threadfin shad. Thirty three threadfin shad from Lake Norman, North Carolina were insonified at 120, 200, and 420 kHz to determine acoustic backscattering cross sections. The measurements covered the range of fish total length (TL) over acoustic wavelength (λ) of 4 <25. The finite bent cylinder and low-resolution acoustic scattering models require conversion of fish body and swimbladder morphology to equivalent cylindrical parameters. There appears to be a direct relationship between fish morphology and cylindrical parameters. The ray-mode model uses the actual morphology of the swimbladder and body. Probability density functions (PDF’s) from the same fish at 120 and 420 kHz support the idea that knowledge of fish orientation in the field is important and the effect of orientation becomes more significant at higher frequencies. The scattering curves can be used in the inverse method along with multiple frequency sonar systems to investigate the adequacy of classification and identification of fish.