When the ultrasonic source moves relative to the observer, the frequency received by the observer will be different from the frequency of the ultrasonic source. Therefore, the small particles and bubbles that move with the water relative to the ultrasonic transducer will also change the receiving frequency of the transducer, and increase with the increase of the floating velocity in the water, thus measuring the Doppler frequency shift and the water velocity at the point where the Doppler ocean-current meter is located is also measured. It is mainly used for irrigation open channels, municipal sewer pipes, hydrological basins and other occasions. It is especially suitable for occasions with low water level, and it can work when the water level exceeds 15 cm. In regular pipelines and channels, the water depth is measured by the pressure sensor on the flow meter, and the flow velocity is measured by the ultrasonic sensor, and then the flow rate can be easily calculated.

When the ultrasonic source moves relative to the observer, the frequency received by the observer will be different from the frequency of the ultrasonic source. Therefore, the small particles and bubbles that move with the water relative to the ultrasonic transducer will also change the receiving frequency of the transducer, and increase with the increase of the floating velocity in the water, thus measuring the Doppler frequency shift and the water velocity at the point where the Doppler ocean current meter is located is also measured. It is mainly used for irrigation open channels, municipal sewer pipes, hydrological basins and other occasions. It is especially suitable for occasions with low water level, and it can work when the water level exceeds 15 cm. In regular pipelines and channels, the water depth is measured by the pressure sensor on the flow meter, and the flow velocity is measured by the ultrasonic sensor, and then the flow rate can be easily calculated.