Coherent Doppler wind lidar has made significant progress in wind profile measurement because of its high temporal and spatial resolution. All-fiber Coherent Doppler wind lidar has caused most interest in mobile wind detection due to its excellent stability and reliability. A theoretical model was analyzed based on the signal-to-noise ratio (SNR) function, the SNR of continuous-wave and pulsed lidar with different focusing distances was evaluated. A 1550 nm all-fiber mobile Doppler wind lidar was designed for wind profile measurement. The system consists of a narrow-linewidth seed laser, a single-mode fiber amplifier, transceiver optics, and a data processing system. In order to verify the performance of the mobile laser lidar, a velocity calibration experiment was carried out on a moving car with a speed of 10-30 m/s in December 2020. The wind velocity of laser lidar and ultrasonic anemometers was measured and compared with a different elevation angle of laser. Results show good agreement between both measurements. The correlation coefficient is great than 0.96, and the standard deviation of velocity is less than 0.79 m/s.
A 2 μm single-frequency, all-solid-state laser is one of the preferred light sources for coherent laser wind lidar and differential absorption lidar. In order to obtain 2 μm single frequency pulse laser with the high energy and hundred nanoseconds pulse width, the Ho:YAG non-planar ring cavity laser pumped by Tm:YLF solid state laser was used as the seed source to design and develop an injection-seeding single frequency Q-switched Ho:YAG pulse laser. A 2090 nm single-frequency pulse laser with an average pulse energy of 18.51 mJ and pulse width of 110.9 ns was obtained at a repetition rate of 200 Hz. The beam quality M2 factors of the output laser are 1.16 in the X direction and 1.25 in the Y direction, and the pulse spectrum width is 4.05 MHz.
Coherent wind lidar is suitable for multiple scenarios. In this paper, a 1.55μm portable wind lidar with 10kHz 10μJ-level 200ns-pulsewidth output was developed. The theoretical model was established based on signal-to-noise ratio (SNR) function and coherent detection principle. The influence of linewidths and pulse widths of single frequency pulsed laser on the wind velocity measurement was studied and verified in comparison experiments. The blind area of the lidar was also analyzed. Solved from spectrum and SNR distribution in range bins, detection range of the lidar is an important detection parameter. The portable wind lidar reached the detection range to 2km with the inclination of 0°, and the range to 1.5km with the inclination of 90°.
A1645nm injection-seeded Q-switched Er:YAG ceramic laser pumped by a 1532 nm fiber laser with changeable pulse repetition frequency (PRF) used for Coherent wind measurement Lidar is demonstrated. Single-frequency operation of Er:YAG laser is achieved by injection seeding technique. A ‘M-shape’ ring cavity is utilized to eliminate the effects of spatial hole burning. The laser delivered single-frequency pulses with energy ranging from 6.6 to 10.2 mJ. The corresponding pulse width and PRF varied between 179 ns-271 ns and 300 Hz-1 kHz, respectively. And the line width at 300 Hz is measured to be 2.82 MHz. The measured M2 factors are 1.51 and 1.54 in x and y directions, respectively.
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.
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