Precise capture of fish movement trajectories in complex environments via ultrasonic signal tag tracking

Ultrasonic tag tracking technology has been widely used in fish behavior research, but most existing studies obtain fish movement trajectories through use of supporting software or post-processing services provided by the manufacturers of the relevant equipment. Articles concerning fish positioning principles and optimization and processing methods suited to complex water environments, are rarely published. This paper proposes a set of solutions permitting precise capture of fish movement trajectories. The proposed methods can effectively mitigate the impact of difficult conditions such as partial loss of time synchronization signals and data containing gross error-bearing observations on the process of locating tagged fish. Test results show that: (1) Even if time synchronization signals for a continuous 2 h period are lost, the accuracy of time synchronization between the hydrophones remains consistent with the requirements of meter-level positioning. (2) The proposed method can effectively detect the existence of gross errors exceeding 10 m in the observation data; the success rate of the method in identifying unique gross error-bearing observations was 99.7%. (3) Based on existing hydrophones with millisecond-level observation precision, three-dimensional (3D) positioning of fish-borne signal tags to 2˜5 m precision is possible.