| 摘要 |
PURPOSE:To identify the sea bottom and school of fish thereon clearly by detecting a signal from the sea bottom through an integrating circuit or the like with a specified time constant. CONSTITUTION:Pulses received from an ultrasonic transmitter 1 is applied to an integrating circuit 4 whose time constant is identical to the leading edge gradient of a sea bottom signal B2 via a pulse shaping circuit 3 or the like and the integration output (d) is sliced with a slicing circuit 6 as reaching a specified level after a fixed time passes. The output (e) of the circuit 6 controls a gate 8 to which pulses (f) received via a delay circuit 7 so that a sea bottom singnal G1 is recorded at a fixed level. On the other hand, when school of fish exist on the sea bottom, it elongates the time until the output (d) reaches the specified level. Thus, a signal for school of fish on the sea bottom greater than the signal G1 is recorded whereby a clear indentification is established between the sea bottom and the fish thereon. |
