Study Of Atmospheric Aerosols Based On A Dual Field-of-view Lidar

Atmospheric aerosols are small particles suspended in the atmosphere. Atmospheric aerosols’ absolute quality is tiny, but they can directly affect climate change and radiative transfer by scattering and absorption of solar and terrestrial radiation, and also indirectly affect the radiation by affecting cloud formation as cloud condensation nuclei. As an active remote sensing instrument, lidar provides a high spatial resolution vertical profile of aerosol optical properties, such as aerosol extinction coefficients, backscattering coefficients and aerosol optical depth which can be applied in atmospheric study and environment monitoring. So lidar becomes more and more popular in the atmospheric research domain.The lidar equation shows that the power of the received signal rapidly falls with an increase in range, and the dynamic range is large. It is difficult to achieve the cover from lower to higher atmosphere. And the backscattering lidar signal and inversed results are often limited by various noises. Performing a proper pre-processing will improve the quality of the results.This thesis mainly focuses on the detection of atmospheric aerosol of the whole troposphere by a dual field of view lidar. The lidar has two independent receiving channels to solve the problem of the dynamic range, one for the lower atmosphere (especially the planetary boundary layer) by a larger field of view, and the other for higher altitudes by a smaller field of view. Combining these two channels can effectively increase the detection ability of the lidar by hardware approach. Lidar signals are contaminated by local and sky background noise. So we can increase the detection ability of the lidar by software approach, by processing a proper noise reduction algorithm. The detection ability of the atmospheric aerosol optic properties can be effectively increased by dual field of view technology and automatic denosing algorithm. The optic properties of atmospheric aerosol over Wuhan can provide data support to atmosphere, remote sensing, meteorology and environment protection..Firstly, the optic properties of the whole troposphere aerosols are obtained by a dual field of view lidar. The lidar has two independent receiving field of view to solve the problem of the dynamic range, the larger field of view for the lower atmosphere (especially the planetary boundary layer) by lowering the overlap area, and the smaller field of view for higher altitudes by reducing the effect of sky background noise.Secondly, there are two optical receiving system and three data acquisition system in the dual field of view lidar. After the combination of analog detection signal and photon counting signal, near-range channel signal and far-range channel signal, the obtained signals are combined to one signal which covers from atmospheric boundary layer to high atmosphere. The contradiction of lower blind detection zone and higher atmospheric detectiong ability, are resolved by data combination.Thirdly, the lidar noise reduction algorithm are studied by employing the two channel signals with different signal to noise ratio. The denosing algorithm based on empirical mode decomposition (EMD) is applied to lidar signals. It is found that the signal and noise are extracted to one intrinsic mode function (IMF) by the EMD-based denoising, so the threshold method is applied. The results show that the improved method can effectively distinguish the signal and noise.