Size and Angular Location Estimates of Fish Schools Using Spatial Correlation

Computer simulation based on a point scatterer model has been used to investigate the problem of estimating fish school location and dimensions using split-beam processing of hydroacoustic data. Estimates are derived from the temporal crosscorrelation of signals received by transducer halves, the peak correlation amplitude being related to the variance of the scatterer locations (fish school width) and the time shift of the peak being related to the mean of the scatterer locations (fish school angular position). These estimates are formed with vertically and horizontally separated transducer halves and combined with echo arrival time to provide three-dimensional position and size. It is demonstrated that fluctuations in the estimated angular size decrease as the ratio of pulse length to echo length decreases. The effect of additive noise, uncorrelated between acoustic channels, has also been studied. Noise causes width estimates to be biased toward larger values, owing to decorrelation between the acoustic channels. The location estimates, however, remain unbiased for signal-to-noise ratios down to approximately -5 dB.