Key Technologies Of High Spectral Resolution Wind Measurement By Laser With High Stability

Incoherent Doppler wind lidar is currently the only available instrument for wind field measurement in the clear atmosphere. It is capable of obtaining 2D wind field with high spatio-temporal resolution which is essential to numerical weather forecast, atmospheric dynamics and aeronautic security. Furthermore, the system will contribute to the development of the space-borne wind lidar. This paper focuses on the key technologies of operational wind measurement by laser with high stability.This study presents a system design of the lidar for the wind measurement. The experiment of seed injected diode-pump Nd:YAG laser is demonstrated, in which seeder coupling using single-mode polarization fiber is carried out for the first time. The study presents a single frequency, tunable pulse laser system with high reputation to 1 kHz. An iodine-absorption based digital PID controller is also described that is capable of locking the laser frequency at a stability level of better than 1 MHz for arbitrarily long periods.In order to achieve operational measurement, two digital signal processing algorithms are applied for the lidar data processing. Firstly, Empirical Mode Decomposition (EMD) analysis is implemented to improve the SNR of laser backscattering signal. EMD allows unambiguous data reconstruction, and is possibly the only computational method of real time lidar signal processing. Secondly, wavelet analysis is used to improve the accuracy of line of sight (LOS) wind velocity derived from lidar backscattering. The study proposes to use discrete biorthogonal wavelets with a distance-dependent threshold to denoise LOS wind speed that has large dynamic range along the data profile.A modularized design of lidar is presented. All of the sub-systems such as laser transmitter, high spectral resolution iodine filter, photon detector and data acquisition instrument are coupled with fibers and cables, and are able to be independently calibrated. The simulation of the system shows the possibility of the design.