Research on measurements method for fish school migration velocity based on five-beam phased-array

The measurements of fish school migration is very important in the investigation of the distribution of fishery resources, and a measurements method for three-dimensional fish school migration velocity based on five-beam phase-controlled technology is proposed. In the five-beam phased-array fish-finder, a plane phased-array with multi-elements is employed to form the required five beams. No compensation for sound velocity is needed, and all of them beams are used to detect integrated information of fish schools; and, when fish schools can be covered by four peripheral beams simultaneously, the technique can be used to measure the migration velocity. The synthesizing method of directivity for an equal spaced linear array is analyzed on the basis of the concept of a combination array. Then, the scheme to realize five-beam transmitting and receiving is given based on the idea. Finally, the acoustic scattering model of a fish school is established: four peripheral beams are used to obtain an acoustic scattering signal of a fish school with velocity information, and then the fish school migration velocity is calculated.