Echo-sounding equipment

Claim 1

ECHO-SOUNDING EQUIPMENT FOR THE DETECTION OF FISH HAVING ULTRASONIC GENERATING AND RECEIVING APPARATUS FOR TRANSMITTING PULSES OF ULTRASONIC WAVE ENERGY INTO THE SEA AND CONVERTING WAVE ENERGY REFLECTED FROM OBJECTS IN THE SEA INTO ELECTRICAL ECHO SIGNALS, A RECEIVER AMPLIFIER CONNECTED TO THE SAID APPARATUS TO AMPLIFY THE ECHO SIGNALS, A CORRECTION CIRCUIT CONNECTED TO APPLY AN AMPLITUDE-CORRECTION WAVEFORM TO THE RECEIVER AMPLIFIER TO VARY THE AMPLIFICATION OF THE ECHO SIGNALS IN ACCORDANCE WITH THE RANGE FROM WHICH THEY ARE RECEIVED IN SUCH A MANNER AS TO COMPENSATE FOR THE SPREAD OF THE TRANSMITTED WAVE ENERGY AND ITS ABSORPTION IN THE SEA, A SELECTION CIRCUIT ADAPTED TO SELECT FROM THE ECHO SIGNALS A REFERENCE TRIGGER SIGNAL ORIGINATING FROM A REFERENCE DEPTH, A WEIGHTING CIRCUIT CONNECTED TO SAID SELECTION CIRCUIT AND RESPONSIVE TO THE REFERENCE TRIGGER SIGNAL TO GENERATE A WEIGHTING CONTROL WAVEFORM REPRESENTATIVE OF THE DEPENDENCE OF THE PROBABILITY OF CATCH ON DEPTH AND TO MODIFY THE ECHO SIGNALS IN ACCORDANCE WITH THIS WEIGHTING SIGNAL, AND AN INDICATOR CONSTRUCTED TO INDICATE THE ACCUMULATED MAGNITUDE OF THE ECHO SIGNALS WHICH HAVE BEEN AMPLIFIED BY THE RECEIVER AMPLIFIER AND SUPPLIED TO SAID INDICATOR BY SAID WEIGHTING CIRCUIT.