Development of an omnidirectional fishery sonar using digital broadband and multiple beams

In response to the demand for efficient and high-precision detection in marine capture fishery, here the omnidirectional fishery sonar was developed to detect the targets in long distance using digital broadband and multiple beams. Broadband technology was used to effectively suppress the interference of interface and volume reverberation. Multiple beams were to improve the resolution of target detection. A distributed architecture of signal processing was also constructed for the omnidirectional fishery sonar using a field programmable gate array (FPGA). The omnidirectional fishery sonar was divided into multiple sectors. The underwater acoustics was simulated to determine the mutual constraints between the three main influencing parameters, namely the size of the transducer array, the maximum distance of detection, and the optimal point of operating frequency. The key parameters were then selected for the fishery sonar, according to the typical fishery vessels in China. The preferred frequency band of the signal was 20-30 kHz. A systematic investigation was also conducted on the effects of noise, interface reverberation, and volume reverberation on the detection performance of omnidirectional fishery sonar. A parallel and serial broadband beamforming FPGA was utilized to reduce the on-chip storage by 90% during operation; the Delta Sigma module was adopted to improve the signal-to-noise ratio of the transmission signal, where the noise within 20-30 kHz shifted to the frequency band above 50 kHz. A one-step stability of the predictive beam was improved using two-point recursive interpolation. The real-time stability errors of the beam were achieved at less than 1.6° (-0.8°-+0.8°) under significant sway of fishing vessels. The core components were also developed, such as a cylindrical transducer array, a highly integrated receiver and transmitter, and a 256 multi-channel signal processor, and system integration. 256 channels were independent receiving and transmitting for the signals in the 20-30 kHz frequency band. The scanning detection capabilities were for horizontal 360° and vertical 70°. The omnidirectional multi-beam fishery sonar was installed on the deep-sea fishery vessel. Environmental and simulated target detection tests were carried out on the fish school. The sea test results showed that the omnidirectional fishery sonar better performed stable, clear and continuous detection of environmental targets, where the detection ability of the 0 dB fish target reached more than 1 500 m. The key indicators of the self-developed omnidirectional sonar can fully meet the needs of marine fishing scenarios. The finding can greatly improve the detection performance of fishing for large-scale autonomous production.