An algorithm that retrieves aerosol properties from dual‐wavelength polarized lidar measurements
An algorithm that retrieves aerosol properties from dual‐wavelength polarized lidar measurements
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DOI：
10.1029/2006jd007435
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发表时间：
2007-03
影响因子：
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通讯作者：
T. Nishizawa;H. Okamoto;N. Sugimoto;I. Matsui;A. Shimizu;Kazuma Aoki
中科院分区：
文献类型：
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作者：
T. Nishizawa;H. Okamoto;N. Sugimoto;I. Matsui;A. Shimizu;Kazuma Aoki
[1]我们开发了两种算法，利用来自三通道Mie-lidar测量的信息，即在λ=532 nm处的共极化和交叉极化分量以及在λ=1064 nm处的总成分(共极化和交叉极化)，来估计每种气溶胶类型在λ=532 nm处消光系数的垂直分布。在算法中假定了每种气溶胶类型的模式半径、标准差和折射率。该算法的主要特点是：(1)反向算法估计远端总气溶胶的消光系数，而Fernald方法则以远端消光系数作为边界条件。(2)它们确定每一层的气溶胶类型，即水溶性、海盐或尘埃。(3)估算了激光雷达比等气溶胶微物理性质的垂直分布。首先将反向算法应用于仅按光谱与总分量之比进行定标的激光雷达信号，以求出晴空条件下的定标常数和气溶胶特性。然后，利用正演算法对云底下的气溶胶特征进行反演。我们进行了密集的误差分析。当测量误差为±5%时，消光系数中各气溶胶组分的测量误差分别小于20%(50%)。通过与海上天空辐射计测量数据的对比验证表明，后向(前向)算法的光学厚度在2%(10%)以内。
[1] We developed two types of algorithms, backward and forward, to estimate vertical profiles of extinction coefficient at a wavelength of λ = 532 nm for each aerosol type, using information from three-channel Mie-lidar measurements, i.e., copolarization and cross-polarization components at λ = 532 nm and total component (copolarization and cross polarization) at λ = 1064 nm. The mode radii, standard deviations, and refractive index for each aerosol type are assumed in the algorithms. The algorithms have the following main features: (1) Extinction coefficient of total aerosols at a far end is estimated in the backward algorithm, while the value at a far end is prescribed as the boundary condition in the Fernald method. (2) They determine aerosol types, i.e., water soluble, sea salt, or dust, for each layer. (3) The vertical profiles of microphysical properties of aerosols such as lidar ratio are also estimated. The backward algorithm is first applied to the lidar signals only calibrated for the spectral ratio to the total components to derive the calibration constant and aerosol properties under clear-sky condition. Next, the forward algorithm is used to retrieve aerosol properties under cloud bottom. We performed intensive error analyses. The errors for each aerosol component in the extinction coefficient are found to be smaller than 20% (50%) for the backward (forward) algorithms, respectively, when measurement errors are ±5%. The validation of the algorithms from the comparison against sky radiometer measurements over ocean shows that the optical thickness agrees within 2% (10%) for the backward (forward) algorithms.