PURPOSE: To make it possible to accurately measure bow speed and stern speed by correcting the positional error of angular speed detected by a gyro due to rotation of the earth using latitude information obtained from a navigator.
CONSTITUTION: A transmission circuit 2 amplifies a transmission burst wave received from an operation control circuit 6 and outputs the amplified burst to a transceiver 1 through a transmission/reception switching circuit 3. The transceiver 1 is set at bow and radiates ultrasonic wave obliquely downward 4 into the water. Reflected signal is received by the transceiver 1 and inputted through the switching circuit 3 to a receiving circuit. A frequency counting circuit 5 measures frequencies received in each of four directions and outputs them to the control circuit 6. The control circuit 6 calculates longitudinal and lateral speeds at the bow. A rate gyro 8 delivers an angular speed of stern line to a latitude correction circuit 9. To the correction circuit 9, current latitude of vessel from a navigator is inputted and error of angular speed detected by the gyro 8 due to rotation of the earth is corrected.
SAKUMA TAKESHI
MIYAO YOICHIRO
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