Multi-longitudinal-mode Doppler lidar technology based on quadri-channel Mach-Zehnder interferometer

The detection principle of a multi-longitudinal-mode (MLM) Doppler lidar based on a quadri-channel Mach-Zehnder interferometer (QMZI) was analysed. The measurement error formulas for the radial wind speed and backscatter ratio of this type of Doppler lidar system were derived. The advantages of this detection technology were thoroughly analysed based on the principle. The optical path difference (OPD) 'l' between the two interference arms of the QMZI was optimised. For a detection height of 0-20 km, 'l' was selected as 50 cm to balance the detection of radial wind speed and backscatter ratio. The overall structure of the MLM Doppler lidar based on QMZI was designed, and detailed design parameters of the system were provided. Further simulation was conducted to evaluate the detection performance of the designed QMZI- based MLM Doppler lidar system. The simulation results showed that when using a pulse laser with a power of 17.5 W@355 nm and a telescope with an aperture of 25 cm, a detection zenith angle of 30 degrees, a vertical resolution of 26 m@0-10 km and 52 m@10-20 km and a pulse accumulation time of 1 min, the radial wind speed measurement errors of the system during the day and night were less than 2.1 m/s and 2.5 m/s; the backscatter ratio relative measurement errors were less than 0.81% and 0.97%.