Experimental Research On The Pulse Coherent Accumulation Technology Of Wind Lidar

As the lidar technology and digital signal processing technology developing, the demand of using wind lidar is also constantly improving. Compared with microwave wind radar, wind lidar can work in the clear sky conditions and realize the measurement of radial wind velocity and wind field inversion with high accuracy. The core problem of wind lidar is how to detect the signal of atmospheric aerosol backscattering, due to the atmospheric aerosol scattering cross section is very small, echo signal is very weak. In this paper, we propose a method to achieve coherent accumulation of lidar’s echo signal and complete the detection of weak signal.First of all, this paper reviews the development of domestic and foreign coherent wind lidar, sums up the advantages of coherent detection, discusses the coherent wind lidar signal processing theory, mainly analyzes of the signal coherent accumulation method and frequency transformation theory.Secondly, through the analysis, coherent wind lidar is non-coherent system, acousto-optic frequency shift will bring the random initial phase for each signal waveform, non-coherent will lead to error in the results of echo signal’s coherent accumulation. Through theoretical analysis, a method of the non-coherent system that realizes the detection signal coherent accumulation is proposed. Using lidar system’s strong reflection and orthogonal mixing principle to obtain random initial phase of each waveform, eliminate the random phase, then make phase aligned, waveforms consistent, so as to realize the signal coherent accumulation. The simulation platform of coherent lidar system is built by Simulink toolbox of Matlab, and verify its feasibility. At the same time, compared the SNR of after aligning the phase of the signal accumulation processing with non-aligning the phase of the signal accumulation processing, the results show that pulse coherent accumulation can improve SNR of weak target signal.Finally, a experimental resaerch of signal coherent accumulation is done. Making a improvement in original coherent wind lidar system which uses two balance detectors to receive, the one receive the light beside PBS and the other receive target echo signal light to make coherent accumulation. On the basis of simulation design experiment scheme:the one is a echo signal coherent accumulation experiment by using optical fiber as the ideal channel which avoids the phase damage caused by the atmosphere transmission, the result coincides with the simulation experiment; the other one is atmospheric measurements under field environment, which uses wind lidar system to detect the atmosphere of 90 m, 510 m far away, verify feasibility of coherent signal accumulation method. At the same time, analysis the result, through coherent pulse accumulation SNR increases from-38 d B to 10 d B.