PURPOSE: To enable the measurement of water depth in a wide range along with a smaller size and a lighter weight of transmitters by transmitting a plurality of ultrasonic waves close to each other in the frequency so as to generate a parametric beam.
CONSTITUTION: Transmitters 101, 102, 121 and 122 are so arranged as to transmit high frequency ultrasonic pulse waves close to each other with a specified angle θ of depression each while these waves interfer with each other to generate a parametric beam wave. A receiver (transmitter) receives a reflected wave from a water mass at a specified depth among those specified of the ultrasonic pulse waves and a means S1 detects a signal containing a Doppler shift frequency component of the frequency. Receivers 113, 114, 133 and 134 receives a reflected wave from the water bottom of the parametric beam waves and a means S2 detects a signal containing the Doppler shift frequency component. Then, an arithmetic means CPU calculates the ground velocity of a water flow based on the detection signals of the means S1 and S2.
ENDOU YASUYOSHI
NAKAMURA AKIRA
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