Abstract
The system described is applied in acoustic fish surveys as a digital echo integrator and a data logging system for environmental data. A ship-borne mini computer is interfaced to an echo sounder and a CTD system. Quantification of echo sounder recordings is done by sampling echo level voltage at the output of the echo sounder at a rate of 15 kHz. The samples are converted to digital form, squared and integrated. A software-controlled operating system receives control codes from the operators display terminal. Routines for sampling, processing and output activities are given priority according to their speed requirements by means of the computer's priority interrupt system. Integrals of squared echo voltage values are presented, specified per nautical mile and separated in several depth intervals. These integrals are linearly related to fish density in the depth intervals within the distance integrated. Data of electrical conductivity, temperature and pressure in the sea are transferred to the computer from the CTD deck unit. All CTD data are recorded on magnetic tape, while data at selected pressures are processed and presented in real time.
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