The echo-integration (EI) method is the primary method for fisheries resource surveys by acoustics. Application of the EI results to estimation of individual school abundance and/or to school descriptors for species identification, however, has not been well developed. This paper first considers, based on the basic theory of the EI method, the raw volume backscattering strength of an individual school and the school section scattering strength, both of which are observed by the beam of an echo sounder. Next, approximation methods to estimate the total school scattering strength of an individual school are proposed. The methods are verified by an exact computer simulation of school echoes. The methods are applied to actual echo data obtained by a quantitative echo sounder to confirm the applicability. The section scattering strength is appropriate as an index of school abundance, but the school scattering strength, especially the strength approximated by combining echo sounder data with sonar 3D distribution data, is most appropriate for the abundance index of an individual school.

View full abstract

In this study, we measured temperature dependences of longitudinal and shear wave velocities in some acoustic lens materials using the sing-around method. The materials we tested were silicone rubber (SR) and polymerization acrylic resin (PAR). The velocities were measured in the temperature range from 5℃ to 30℃. The temperature of material immersed in water was maintained by using a water tank that could be kept at a constant temperature while the velocities were measured. The PAR material was made by stacking two thin plates and cementing them together with polymerizing adhesive. We assumed that this material will be used for making large acoustic lenses which cannot be realized with a single plate of PAR. For example, the aperture of such a lens is greater than 1.0 m, and the thickness is over 0.25 m. After measurement of sound velocities of materials, the data of velocities were approximated to the linear function of temperature using regression analysis. The results of PAR were then compared with those of the simple PAR material with a single plate used in the previous studies. In the PAR material, the temperature coefficient of the longitudinal wave was −2.822 [m/s・℃], and that of the shear wave −2.107 [m/s・℃]. On the other hand, the temperature coefficient of the longitudinal wave was −2.545 [m/s・℃], and that of the shear wave was −2.189 [m/s・℃] in the simple PAR material. In the SR material, the temperature coefficient of the longitudinal wave was −2.893 [m/s・℃].

View full abstract