Flow velocity measurement by radar

eTrust Co., Ltd. kindly set up a demonstration of flow velocity measurement by radar at our field site today. A representative from Yokogawa demonstrated an instrument called "Ryukan", which uses non-contact radar technology to measure the surface flow velocity of a river from a bridge. This is extremely useful when rivers are in flood and conditions are too dangerous for the use of conventional flow meters, especially when sediment loads are high and floating debris is a hazard.

The range of flow velocity which can be measured with the instrument is 0.5 m/s to 20 m/s. The sensor is angled at between 30-40 degrees from horizontal, and can be set up in either upstream or downstream directions. With the instrument set up at about 5.5m above the water surface, the target sampling area is elliptical measuring about 1.6m in width and 2.6m in length.

Stage = 51cm, Ta = 10.5C, Tw = 12.5C

We concurrently made a typical discharge measurement using an electromagnetic flow velocity meter and compared measurements made just below the surface with those taken by the radar meter. Even though flow velocities today were at the lower limit of the measuring range for the radar meter, it was impressive how similar the readings were to the sensor in the water. At higher flood stages for which the radar meter is intended, the data recorded is likely to be of much higher accuracy. The radar meter needs roughness elements on the surface of the water, such as ripples and waves, to allow it to obtain an accurate reading.