Research On Key Technologis For Microwave Modulated Lidar And Temperature Lidar

Doppler lidar, which has significant advantages of the high spatial and temporal resolution and the ability of measurements in the clear atmosphere, has been developing rapidly. However there are technical difficulties to achieve high laser frequency stability, longer coherence length and high resolution optical frequency discriminator in Doppler lidar. Thus, the dissertation proposes one novel microwave modulated lidar, which has advantages of detecting molecular and aerosol average speed in clear air, as high sensitivity as microwave coherence detection. The paper developed the sub-receiving module for atmospheric temperature measurement, which expands the capabilities of Doppler lidar. At last, there is significant application to combine microwave modulated and temperature measurement to produce microwave modulated composite lidar.The dissertation consists of three innovations:the first part is to propose the theory of microwave modulated lidar which free the limitation of narrow transmitting linewidth for previous Doppler lidar; the second part is to illustrate the details that how to change the optical Doppler frequency discrimination to the microwave frequency discrimination; the third part is to develop optical receiving module based on single iodine filter for atmospheric temperature measurement. At last three innovations are to to pave the road of microwave modulated composite lidar.One of the main contents of this dissertation is to build an all-optical fiber microwave modulation lidar experimental system. After laser being modulated by microwave, the lidar return has Doppler frequency shift not only in laser carrier frequency but also in microwave signal. As a result, Doppler signal can be extracted from microwave modulation signal. In principle, the transmitting laser is set as the carrier in microwave modulated lidar, while the microwave is regarded as detection signal to probe the speed of object. This method is independent on the optical frequency discriminator and relaxs the limitation of laser linewidth. Theory and experiments demonstrate that velocity field can be extracted from the intensity modulated laser returns by direct detection but the phase modulated laser returns. The dissertation simulates the detection principles and provides the system design, retrieval methods and analysis of signal noise ratio. Simulation results show that 1m/s corresponds to 8.7Hz Doppler frequency shift and velocity measurement range over±2000m/s. During the combination experiments with microwave modulated lidar driver and receiver, all-fiber modulated laser system shows good performance on modulation with velocity measurement precision 0.75m/s (13Hz linewidth at 1.3GHz).Designing and experiments for atmospheric temperature measurement module based on a single iodine filter is the other section of thesis, which is installed on the mobile incoherence Doppler lidar based on the iodine filter frequency discriminator developed by Ocean University of China. It extends the observation capability of Doppler wind lidar and paves the road to multi-function applications. Comparison experiment with radiosonde of meteorological administration of Qingdao shows a good agreement. Temperature lidar receiver gets 1℃standard deviation under 5km altitude and 3℃standard deviation up to 16km.Based on the two sections, the dissertation proposes a composite lidar prototype, which combines the microwave modulation technology and high spectral resolution lidar to make best of advantages of heteotodyne speed detection and temperature measurement. Succeeding development will show the perspective of this noval composite lidar.