Comparison of CALIPSO aerosol optical depth retrievals to AERONET measurements, and a climatology for the lidar ratio of dust
Comparison of CALIPSO aerosol optical depth retrievals to AERONET measurements, and a climatology for the lidar ratio of dust
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DOI：
10.5194/acp-12-7431-2012
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发表时间：
2012-01-01
影响因子：
6.3
通讯作者：
Trepte, C.
中科院分区：
文献类型：
--
作者：
Schuster, G. L.;Vaughan, M.;Trepte, C.
我们将0.532 μ m的CALIPSO柱气溶胶光学深度与147个AERONET站点的测量结果进行了比较，这些数据同步于3年期间卫星立交时间的30分钟内。我们发现了677个合适的立交桥，相对于AERONET，整个数据集的CALIPSO偏差为-13%；相应的绝对偏差为-0.029，均值的标准差（SDOM）为0.014。因此，零假设在97%的置信水平上被拒绝，这表明数据集之间存在统计学上显著的差异。然而，如果我们从分析中省略含有灰尘的CALIPSO列，则449个立交桥的相对和绝对偏差将减少到-3%和-0.005，标准误差为0.016，并且零假设拒绝的统计置信水平降低到27%。对CALIPSO气溶胶的6个亚型进行分析，发现仅含有粉尘亚型的大气柱相对偏差为-29%，绝对偏差为-0.1，相关系数R = 0.58；这表明，CALIPSO尘埃检索的假设激光雷达比（40 sr）可能过低。因此，我们使用AERONET的尺寸分布、折射率、百分比球体和球体和球体的前向光学代码来计算位于尘埃带的AERONET站点的激光雷达比气候学。我们分析的最高激光雷达比率出现在北非的非萨赫勒地区，在229次检索中，0.532 μ m的中位数激光雷达比率为55.4 sr。非洲萨赫勒（49.7 sr， 929次检索）、中东（42.6 sr， 489次检索）和印度坎普尔（43.8 sr， 67次检索）的激光雷达比率略低。我们将激光雷达比的区域变异性归因于尘埃实际折射率的区域变异性，因为这两个参数高度反相关（各个区域的相关系数范围为-0.51至-0.85）。AERONET折射率的变化与沙尘带中伊利石浓度的变化一致。
We compared CALIPSO column aerosol optical depths at 0.532 mu m to measurements at 147 AERONET sites, synchronized to within 30 min of satellite overpass times during a 3-yr period. We found 677 suitable overpasses, and a CALIPSO bias of -13% relative to AERONET for the entire data set; the corresponding absolute bias is -0.029, and the standard deviation of the mean (SDOM) is 0.014. Consequently, the null hypothesis is rejected at the 97% confidence level, indicating a statistically significant difference between the datasets. However, if we omit CALIPSO columns that contain dust from our analysis, the relative and absolute biases are reduced to -3% and -0.005 with a standard error of 0.016 for 449 overpasses, and the statistical confidence level for the null hypothesis rejection is reduced to 27%. We also analyzed the results according to the six CALIPSO aerosol subtypes and found relative and absolute biases of -29% and -0.1 for atmospheric columns that contain the dust subtype exclusively, but with a relatively high correlation coefficient of R = 0.58; this indicates the possibility that the assumed lidar ratio (40 sr) for the CALIPSO dust retrievals is too low. Hence, we used the AERONET size distributions, refractive indices, percent spheres, and forward optics code for spheres and spheroids to compute a lidar ratio climatology for AERONET sites located in the dust belt. The highest lidar ratios of our analysis occur in the non-Sahel regions of Northern Africa, where the median lidar ratio at 0.532 mu m is 55.4 sr for 229 retrievals. Lidar ratios are somewhat lower in the African Sahel (49.7 sr for 929 retrievals), the Middle East (42.6 sr for 489 retrievals), and Kanpur, India (43.8 sr for 67 retrievals). We attribute this regional variability in the lidar ratio to the regional variability of the real refractive index of dust, as these two parameters are highly anti-correlated (correlation coefficients range from -0.51 to -0.85 for the various regions). The AERONET refractive index variability is consistent with the variability of illite concentration in dust across the dust belt.