The Research On All Fiber Coherent Wind LIDAR

Currently, the wind LIDAR is always an irreplaceable solution to the real-time, multi-scale wind sensing on a sunny day. It have an encouraging prospect on civil aviation, aviation insurance, and numerical weather prediction, military insurance. All fiber coherent wind LIDAR is an upgrade on the basis of the traditional free-space coherent wind LIDAR based on the development of the passive fiber component. Compared with the traditional system, the new system could offer a better performance in a worse circumstance.due to the fact that fiber route for laser is immune to the change of condition of LIDAR.At the beginning of this dissertation, the common passive and active wind sensor is talked about. The disadvantage and advantage are analyzed in the field of active wind LIDAR, and a summarization about the present wind LIDAR at home and abroad is given.In order to get an overall view of all fiber coherent wind LIDAR, firstly the principle and structure of an all fiber coherent LIDAR is introduced, secondly some details about a LIDAR is presented. Such as, a usual LIDAR include four subsystem such as laser emit, laser receive, data sampling, signal processing. The key functions and specifications of different sub-system and important component or the algorithm of spectrum estimate.For the aim to build an all fiber coherent LIDAR, some researches under the simulation system is made involved in the noise-signal ratio, the laser-coupling efficiency, the relationship between the strength of return power and noise-signal ratio according to the change of the focused distance in a focused all fiber coherent wind LIDAR. The extinction ratio of AOM and the strength of local laser to this system, when it get the best performance. The results show that when the local laser reach 730uW and 700uW, the pulsed and CW wind LIDAR get its best respectively, the extinction ratio should be more than -90dB for a pulsed wind LIDAR.In the end, the specifications of the key component that include narrow-linewidth fiber laser, PM fiber circulator, AOM adjustable telescope,balanced detector is introduced according to the result of simulation of chapter 3. In this dissertation, an experimental CW wind velocimetry and pulsed wind LIDAR is built. The speed of air is measured ranging from 45m to 300m by the pulsed LIDAR system, in the later the pulsed fiber laser contains a random sub-pulse after the main-pulse due to a lower extinction ratio of AOM used in this pulsed laser. Some experiments have been made on the strength of sub-pulse and its effect to this pulsed system. In the CW velocimetry system, the accuracy of this system is standardized according to the experimental data from a moving wheel, the result show a 0.07m/s measurable precision of speed. Vapor emitted by a humidifier and wind in the air declare that a good agreement between the measured and really speed. A wind from different directions is also measured using a CW LIDAR system with an extra AOM in the local power compare to the old CW LIDAR.