Application of dual-beam and split-beam target tracking in fisheries acoustics

Dual-beam and split-beam acoustical techniques were originally developed to provide direct in situ measurements of the target strength of individual fish and plankton. The amount of information that can be extracted from these acoustic systems can be significantly increased when the techniques are used in conjunction with ping-to-ping target tracking. For example, target tracking can be used to isolate multiple target-strength measurements from an individual fish or plankton. These measurements can then be averaged to provide a lower variance estimate of the target strength. The measurement of the angular location of the target provided by split-beam systems further enhances the usefulness of tracking. The angular data measured on subsequent pings can be used to resolve returns from single and multiple targets and estimate the direction and speed of the fish as they pass through the beam. Information on fish speed and direction is particularly useful for fixed location acoustic studies. This paper uses a combination of actual data, simulation results, and analysis to describe the various applications and expected performance of acoustic systems that combine dual-beam and split-beam techniques with target tracking. (C) 1996 International Council for the Exploration of the Sea