光学学报, 2017, 37 (1): 0101002, 网络出版: 2017-01-13
两种模拟水云对偏振激光雷达退偏振的蒙特卡罗方法研究
Study on Two Monte Carlo Simulation Programs of Polarization Lidar Depolarization by Water Cloud
大气光学 激光雷达 水云 偏振 蒙特卡罗方法 多次散射 atmospheric optics lidar water clouds polarization Monte Carlo method multiple scattering
摘要
激光雷达探测水云时, 多次散射会使雷达回波产生退偏振效应, 云层对激光的退偏振比与云层微物理特性信息含有特定的关系, 利用这种关系可以反演云层的微物理特性, 但是这种关系需要利用理论模拟进行研究和探索, 理论模拟激光雷达退偏振效应的方法主要是蒙特卡罗方法。给出了两种不同思路的蒙特卡罗模拟方法:一是通过跟踪光子在每一次散射后, 由光子方向矢量和Z轴构成的子午面来模拟, 光子相对于子午面的偏振状态由斯托克斯参量表示; 二是将光子的偏振状态用一个三元单位矢量组来表示, 每次散射后, 根据统计抽样得到的散射角和方位角对其进行旋转, 从而跟踪光子偏振态的变化。给出了详细的模拟过程, 并利用两种方法分别计算了水云的退偏振比, 模拟结果显示这两种方法得出的结果完全一致。
Abstract
The lidar returns exist a depolarization signal in water clouds due to the occurrence of multiple scattering when detecting water clouds. There exist some relationships between depolarization ratio and the microphysics characteristics of water clouds, and they can be used to retrieve the microphysics characteristics of water clouds. However, the relationships must be studied and explored by theoretical simulations. An important method used to simulate the lidar depolarization is Monte Carlo method. Two Monte Carlo simulation programs based on different ideas are given. The first approach is based on tracking the meridian plane described by the photon direction vector and the Z-aixs after each scattering step, and the polarization relative to the new meridian plane is described by the Stokes vector. The second approach is based on the following idea, the polarization state of the photon is described by a triplet of unit vectors rotated by an azimuth and scattering angle after each scattering step so as to track the polarization state change of the photon. A detailed simulation process is given for each approach, and the depolarization ratio for a type of water clouds is calculated using these two approaches. The simulation results show that the results calculated by the two Monte Carlo methods are in good agreement.
孙贤明, 王海华, 申晋. 两种模拟水云对偏振激光雷达退偏振的蒙特卡罗方法研究[J]. 光学学报, 2017, 37(1): 0101002. Sun Xianming, Wang Haihua, Shen Jin. Study on Two Monte Carlo Simulation Programs of Polarization Lidar Depolarization by Water Cloud[J]. Acta Optica Sinica, 2017, 37(1): 0101002.