Fast Lidar and Radar Multiple-Scattering Models. Part II: Wide-Angle Scattering Using the Time-Dependent Two-Stream Approximation
Fast Lidar and Radar Multiple-Scattering Models. Part II: Wide-Angle Scattering Using the Time-Dependent Two-Stream Approximation
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DOI：
10.1175/2008jas2643.1
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发表时间：
2008-12
影响因子：
3.1
通讯作者：
R. Hogan;A. Battaglia
中科院分区：
文献类型：
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作者：
R. Hogan;A. Battaglia
摘要来自液态水云的星载激光雷达回波包含来自光子的重要贡献，这些光子经历了许多广角多次散射事件，导致回波似乎起源于远远超出云端的地方。对深对流云的星载毫米波雷达观测也出现了类似的影响。描述了一种计算这种介质随时间变化的回波的有效方法，方法是将光子分成两类，一类是以近直接路径往返于单一后向散射事件的光子(在激光雷达的情况下，如本文第一部分所述，考虑了途中的小角度前向散射)；另一类是经历过广角多次散射事件的光子。本文描述了用含时双流近似对后一种情况进行建模，将问题归结为求解一对耦合的偏微分方程组，该偏微分方程组中的光子能量往返于能级。
Abstract Spaceborne lidar returns from liquid water clouds contain significant contributions from photons that have experienced many wide-angle multiple-scattering events, resulting in returns appearing to originate from far beyond the end of the cloud. A similar effect occurs for spaceborne millimeter-wave radar observations of deep convective clouds. An efficient method is described for calculating the time-dependent returns from such a medium by splitting the photons into those that have taken a near-direct path out to and back from a single backscattering event (in the case of lidar, accounting for small-angle forward scatterings on the way, as described in Part I of this paper) and those that have experienced wide-angle multiple-scattering events. This paper describes the modeling of the latter using the time-dependent two-stream approximation, which reduces the problem to solving a pair of coupled partial differential equations for the energy of the photons traveling toward and away from the instrum...