Accumulative uncertainties in the quantitative evaluation of signals from fish

The accuracy of the acoustical method used in quantitative assessment of fish populations is mainly dependent on the measurement of the time varying echo signals and the evaluation of the fish target strengths. Various types of accumulative uncertainties involved in the measurement and estimation of different physical variables associated with the two way propagation of the acoustic signals between the fish target and the echo sounder system are investigated in this paper. The accumulative uncertainties are so high that an attempt to obtain an accuracy of, say, 0.5 dB in the conventional target strength calibration routines would have little meaning for any practical fishstock assessment survey. A new dynamic calibration method is proposed and discussed.