Design And Experiment Research On Frequency Discri-Mination For A Doppler Wind Lidar

The change of winds velocities in lower atmosphere is the most dangerous factor during the flying-off and landing of aeroplanes. So it is important for us to detect the change in order to escape from the danger forwardly. We can classify the lidar as coherent and incoherent (direct-detection) lidar on the base of operating principles. In this dissertation I studied the frequency discrimination system based on the Fabry-Perot etalon double-edge technique to detect the Mie scattered signal. The frequency discrimination system is one of the pivotal techniques for Doppler winds measuring Lidar. It can analyze the frequency shift from the variety of intensity. And the capability of frequency discrimination will influence the sensitivity of winds measurement of Lidar.This disseratation mainly studied the frequency discrimination system of winds measurement lidar. The aerosol-molecular ratio of the returned signals in the vertical distance of one and two kilometers has been calculated and simulated, and the error of the wind measuring of several wavelengths has been calculated, based on which we chose 1.06μm wavelengthed laser as the initial detection light. Using double-edge detection theory, we simulated the performance parameters of the frequency discrimination system. We also simulated the effect of dymanic range on the sensitivity and the the effect of incident angle and divergence angle on the error of the measurement. According to the results, we picked up the proper FWHM and the spacing of the central frequence of the two edges. Then we chose the parameters of the F-P etalon and built the system.The experimental scheme is designed to measure the rotational speed of the hard target with our frequency discrimination system. We measured the transmission of the F-P etalon as the function of the incident angle at first, and chose the original operating point based on the results. At that point we measured the backscattered signals from the hard target when it is moveless, turning clockwise and turning counter clockwise. And then we got the rotational speeds of the target from the data we measured. Compairing the speeds with the rotational speeds we measured using a revolution counter, we can finally get the accuracy of our system and prove the feasibility of the frequency discrimination system we designed.