Research on velocity calibration of an eye-safe all-solid-state coherent Doppler wind lidar

Abstract

Long-range wind sensing using coherent Doppler lidar is attractive in many fields such as wind shear warning, aerosol detection and aircraft wake vortex detection. Recently, single frequency, all-solid-state laser around 1.6 μm has caused great interests for its eye-safety and high pulse energy. Velocity accuracy which is one of the key factors of wind lidar systems needs to be calibrated. The 1645 nm eye-safe coherent Doppler wind lidar based on injection-seeded technique consists of laser systems, transceiver optics, and data processing systems is developed. The average power of the laser pulses is 2.6 W with a pulse width of 190 ns at a repetition rate of 300 Hz. The accuracy of velocity measured by the lidar system is calibrated with a velocity calibrator based on a servo motor with a maximum speed of 3000 r/min and a rotating disk with a diameter of 300 mm. A real-time display software based on the LabVIEW platform is designed to get the velocity results and signal to noise ratio (SNR) from the FPGA acquisition module, and the central frequency correction algorithm is used to eliminate frequency jitter of the laser. To calibrate the wind velocity near 0 m/s, a nonmoving hard target at the range of 1.2 km with an elevation angle of about 0.5 deg is measured. Results show that a velocity accuracy (standard deviation of the measurement errors) of 0.38 m/s in the range ±40 m/s and the accuracy of zero velocity is 0.16 m/s.