Abstract :
The echo-counting system to be described was designed for use in conjunction with a high-frequency (100 kHz) echo-sounder and was primarily intended for use in surveying pelagic fish stocks. The counter incorporates a variable gating system, synchronized to the transmission pulse repetition frequency, enabling signals occurring between any twoselected depth limits to be processed. Time-swept gain amplifiers are utilized to compensate for fall-off of signal strength with depth, although the counter differs from previously published systems in as much as echo duration rather than echo amplitude is the parameter under consideration. The processed signal information is displayed as an in-line digital readout from a conventional sealer. A permanent record is obtained from a printer coupled to the sealer.
