Does the velocity coefficient of a Doppler radar flowmeter need field calibration? How is a gauging-based calibration performed?

Yes. Radar measures surface velocity at a point; converting it to cross-sectional mean velocity requires a coefficient K, theoretically in the 0.85–0.95 range. HZ-KSLF ships with the COSP model pre-loaded with a dynamic K relationship for standard sections (rectangular/trapezoidal), so regular lined canals can go straight into service. Natural rivers, compound sections and channels with unusual roughness, however, must be field-calibrated before commissioning — otherwise systematic error can exceed 10%.

Standard calibration procedure:

• Pick a stable mid-flow period and gauge the section with a current meter (rotor or acoustic, multi-vertical multi-point method per GB 50179), recording HZ-KSLF surface velocity and level simultaneously. Cover at least low, mid and high stages with three or more gaugings each.
• Divide the measured mean velocity by the radar surface velocity and regress the K-value curve for the section (how K varies with stage).
• Write the section geometry (bed width, side slopes, roughness) and the K curve into the COSP model with the configuration software, or push it remotely through an EC32/EC60 series RTU.
• Run one or two verification gaugings afterwards; flow deviation should converge within ±5%. Key metering stations targeting ±2–3% need denser calibration.

Recalibration cycle: quarterly during the first hydrological year, then once before each flood season once K proves stable. Re-calibrate immediately whenever the section scours or silts, lining is damaged, or new structures are built upstream or downstream. Gauging records can be exported over the RTU's Modbus/4G channel for hydrological review and archiving.

For more details, visit our product pages or contact our technical team.