MERIS albedo climatology for FRESCO+ O2 A-band cloud retrieval
MERIS albedo climatology for FRESCO+ O2 A-band cloud retrieval
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DOI：
10.5194/amt-4-463-2011
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发表时间：
2010-10
影响因子：
3.8
通讯作者：
C. Popp;Ping Wang;D. Brunner;P. Stammes;Yipin Zhou;M. Grzegorski
中科院分区：
文献类型：
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作者：
C. Popp;Ping Wang;D. Brunner;P. Stammes;Yipin Zhou;M. Grzegorski
抽象。本文介绍了一种新的氧气A波段云反演的全球大气气候学。气候学是基于中分辨率成像光谱仪（MERIS）Albedomap数据，其有利的影响，云分数的推导证明了FRESCO+（快速检索方案云从氧气A波段）算法。迄今为止，FRESCO+中使用的是来自GOME（全球臭氧监测实验）的相对粗糙分辨率（1° × 1°）的地表反射率数据集。GOME LER气候学没有考虑到为痕量气体遥感设计的UV/维斯仪器通常具有较高的空间分辨率，这会引入一些人为因素，例如在海岸线等光谱对比鲜明的地区或明亮的表面目标上。因此，MERIS的黑天区（BSA）从2002年10月至2006年10月期间的数据汇总到0.25° × 0.25°的网格，为每年的每个月和不同的光谱通道。与其他可用的表面反射率数据集相反，MERIS包括754 nm和775 nm的通道，这些通道靠近O2 A波段云检索所需的光谱窗口。MERIS BSA在近红外与中分辨率成像光谱仪（MODIS）导出的BSA相比，平均差异低于1%，相关系数为0.98。然而，当涉及MERIS BSA GOME LER一个明显较低的相关性（0.80）和增强的scatterisfound. Effective云分数从两个示例性的月（2006年1月和7月）的扫描成像吸收光谱仪的大气制图（SCIAMACHY）数据，随后与FRESCO+和海德堡迭代云检索实用程序（MATRRU）算法相比。MERIS气候学总体上改善了FRESCO+有效云分数。特别是小的云分数更好的协议与ECORU。这对于依赖于小云量下准确云信息的大气痕量气体反演具有重要意义。此外，由GOME LER引入的沿沿着的高估和热带辐合带的低估也被消除。虽然在撒哈拉沙漠和阿拉伯半岛的有效云分数成功地减少在1月，他们仍然是太高，7月相对于FRESCO+的高反射目标和不适当的气溶胶信息，阻碍了准确的反云计算检索的反云计算不准确性的大的敏感性。最后，NO2对流层垂直柱密度和O3总柱的推导与FRESCO+云参数从新的数据集，它被发现，MERIS BSA气候学具有显着的和有益的影响，在区域尺度上。除了FRESCO+之外，新的MERIS数据集还适用于使用O2 A波段或477 nm附近的O2-O2吸收波段的任何云检索算法。此外，BSA在442 nm处的副产物可用于NO2遥感，620 nm、665 nm和681 nm处的BSA可用于当前H2O反演。
Abstract. A new global albedo climatology for Oxygen A-band cloud retrievals is presented. The climatology is based on MEdium Resolution Imaging Spectrometer (MERIS) Albedomap data and its favourable impact on the derivation of cloud fraction is demonstrated for the FRESCO+ (Fast Retrieval Scheme for Clouds from the Oxygen A-band) algorithm. To date, a relatively coarse resolution (1° × 1°) surface reflectance dataset from GOME (Global Ozone Monitoring Experiment) Lambert-equivalent reflectivity (LER) is used in FRESCO+. The GOME LER climatology does not account for the usually higher spatial resolution of UV/VIS instruments designed for trace gas remote sensing which introduces several artefacts, e.g. in regions with sharp spectral contrasts like coastlines or over bright surface targets. Therefore, MERIS black-sky albedo (BSA) data from the period October 2002 to October 2006 were aggregated to a grid of 0.25° × 0.25° for each month of the year and for different spectral channels. In contrary to other available surface reflectivity datasets, MERIS includes channels at 754 nm and 775 nm which are located close to the spectral windows required for O2 A-band cloud retrievals. The MERIS BSA in the near-infrared compares well to Moderate Resolution Imaging Spectroradiometer (MODIS) derived BSA with an average difference lower than 1% and a correlation coefficient of 0.98. However, when relating MERIS BSA to GOME LER a distinctly lower correlation (0.80) and enhanced scatter is found. Effective cloud fractions from two exemplary months (January and July 2006) of Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) data were subsequently derived with FRESCO+ and compared to those from the Heidelberg Iterative Cloud Retrieval Utilities (HICRU) algorithm. The MERIS climatology generally improves FRESCO+ effective cloud fractions. In particular small cloud fractions are in better agreement with HICRU. This is of importance for atmospheric trace gas retrieval which relies on accurate cloud information at small cloud fractions. In addition, overestimates along coastlines and underestimates in the Intertropical Convergence Zone introduced by the GOME LER were eliminated. While effective cloud fractions over the Saharan desert and the Arabian peninsula are successfully reduced in January, they are still too high in July relative to HICRU due to FRESCO+'s large sensitivity to albedo inaccuracies of highly reflecting targets and inappropriate aerosol information which hampers an accurate albedo retrieval. Finally, NO2 tropospheric vertical column densities and O3 total columns were derived with the FRESCO+ cloud parameters from the new dataset and it is found that the MERIS BSA climatology has a pronounced and beneficial effect on regional scale. Apart from FRESCO+, the new MERIS albedo dataset is applicable to any cloud retrieval algorithms using the O2 A-band or the O2-O2 absorption band around 477 nm. Moreover, the by-product of BSA at 442 nm can be used in NO2 remote sensing and the BSA at 620 nm, 665 nm, and 681 nm could be integrated in current H2O retrievals.