Evaluation of target angular position algorithms for multi-beam fishery sonars

Two methods for measuring the angular position of a reference target when observed with a horizontally transmitting, multi-beam fishery sonar are described. The theory behind realizations of both a Split-Beam (SB) algorithm and an Interpolated Neighbouring Beam (INB) algorithm is described for a cylindrical transducer array. The algorithms were implemented on both simulated and real data collected during field calibrations. The estimated precision was ±0.2 to ±0.25°, for both algorithms when the target was within the central part of the beam. The precision was reduced for targets with large inclination angles, or in the beam-overlap region of the SB's two half-transducer arrays. The SB algorithm provides an accurate target location within the entire main lobe of the acoustic beam. For the INB method, the accuracy is only good within a small sector close to the acoustic axis, or within ±1.5°-±2.5° depending on the sonar operating frequency. Repeated calibration trials have shown that the SB algorithm can be used to track the reference-target position in real-time with adequate accuracy for use on fishery acoustic surveys.