LAUSR

River discharge measurement is of great significance, and as such, many methods and measuring instruments have been developed by many hydrologic researchers. However, most commonly used measuring instruments must be in contact with the water and are difficult to place and maintain. In this letter, a noncontact measurement method is proposed using ultrahigh- frequency (UHF) radar. The index-velocity method is employed to calculate the mean cross-sectional velocity, and the water-surface velocities on the cross section detected by the UHF radar are used to select the optimum index velocity. A field experiment was conducted in the Hanjiang River at Xiantao, Hubei, China, from March to July 2018. Data from March to June were processed for selecting the optimum index velocity, and the maximum water-surface velocity of the cross section was proven to be optimal. The fit relationship between the mean cross-sectional velocity and the index velocity was used to estimate the mean cross-sectional velocities and river discharges for June to July. The results were compared with those provided by the Hubei Xiantao hydrologic station, and the errors were mostly within ±5%. This confirms that the UHF radar can be used to accurately, automatically, and continuously measure river discharge.