Calibration Technology for a Radar Surface Velocimeter

In Taiwan, climate change exacerbates challenges such as steep slopes, rapid flow, landslides, and erosion, leading to more extreme hydrological events. River flow monitoring during typhoons and floods is difficult, often relying on propeller current meters. High flow velocities pose measurement challenges. Since 2005, handheld radar surface current meters have been used for flow velocity observation at hydrological stations. However, radar surface velocimeters (RSVs) lack suitable calibration equipment. This study proposes an annular flume for high-speed calibration (up to 20 m/s), fixing the velocimeter onto rotating platforms to establish a linear relationship between flow velocity and platform rotational speed. Optical validation confirmed its calibration suitability. Calibration errors include rotational speed, velocimeter angle, water surface distance, perturbations, and sediment concentration. The stable rotating platform provides reliable calibration, with optimal conditions at a 45° angle and 0.5–1.0-m distance. Water fluctuations impact velocimeter sensitivity; suspended particles improve stability. The annular flume design effectively calibrates radar surface velocimeters for high-speed measurements, addressing measurement challenges. This study provides critical insights for hydrological observations in Taiwan’s challenging terrain.