| 摘要 |
PURPOSE:To effectively separately record a marine bottom and a ground rope in the vicinity of the marine bottom by extracting an echo signal from the rope and time controlling to reduce the gain of a receiver during predetermined time from the extracting time. CONSTITUTION:When transmitting information collected upon downward search from an inlet of a dragnet to a master ship to record and indicate it on a recorder in the ship, an echo signal G is extracted from the ground rope of the dragnet to time control to reduce the gain of a receiver 23 during predetermined time TG from the extracting time. Since the receiver 23 lowers its gain when receiving echo signals G, S from the ground rope and the marine bottom, the echo signal G of the ground rope becomes weak with the result that no tail is drawn on the resultant record on the recorder. Accordingly it becomes a fine line, which can clearly isolate from the line showing the marine bottom. Accordingly, the ground rope can be lowered to the vicinity of the marine bottom to effectively obtain fish. |
