利用静止卫星MTSAT反演大气气溶胶光学厚度

卫星遥感是获取气溶胶光学特性的重要手段,利用静止卫星可见光通道资料反演气溶胶光学厚度(AOD)的算法使用日本静止气象卫星MTSAT可见光通道资料反演了2008年5月中国地区陆地上的气溶胶光学厚度,将得到的结果分别与AERONET站点的地面观测值进行比较,得到了较好的线性相关关系,再将其与相应的MODIS气溶胶光学厚度产品进行比较,也得到了较为一致的分布,表明MTSAT反演的气溶胶光学厚度产品可以反映大气气溶胶光学厚度的日变化信息。最后对这种反演算法的误差来源进行了分析。     

Retrieval of aerosol optical properties over the Beijing area using POLDER/PARASOL satellite polarization measurements

Aerosol optical properties over Beijing and Xianghe under several typical weather conditions (clear sky, light haze, heavy pollution and dust storm) are derived from POLDER (POLarization and Directionality of the Earths Reflectances)/PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) multi-directional, multi-spectral polarized signals using a more reliable retrieval algorithm as proposed in this paper. The results are compared with those of the operational retrieval algorithm of POLDER/PARASOL group and the ground-based AERONET (AErosol RObotic NETwork)/PHOTONS (PHOtometrie pour le Traitement Operational de Normalisation Satellitaire) measurements. It is shown that the aerosol optical parameters derived from the improved algorithm agree well with AERONET/PHOTONS measurement. The retrieval accuracies of aerosol optical thickness (AOT) and effective radius are 0.06 and 0.05 mu m respectively, which are close to or better than the required accuracies (0.04 for AOT and 0.1 mu m for effective radius) for estimating aerosol direct forcing.     

单星多角度法同时反演气溶胶光学厚度和地表反射率

尝试以单星多角度卫星观测数据同时反演晴空陆地的气溶胶光学厚度和地表反射率,并选取2009年5月的MODIS(Moderate Resolution Imaging Spectroradiometer)1B资料进行了反演试验.结果表明:单星多角度法反演得到的气溶胶光学厚度结果与MODIS气溶胶产品(MOD04)平均值的相关系数为0.7914;反演的地表反射率结果与MODIS地表反射率产品(MOD09)也具有较好的一致性.对直接利用单星多角度观测数据反演获得一段时间内平均的气溶胶光学厚度进行了有益的尝试.     

A method for spaceborne synthetic remote sensing of atmospheric aerosol optical depth and vegetation reflectance

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非洲地区大气气溶胶光学厚度时空变化及亚速尔高压对沙尘越大西洋传输的影响

研究了非洲地区大气气溶胶光学厚度（AOD）的时空变化及沙尘气溶胶越大西洋海区的传输。结果表明：1）源于撒哈拉沙漠的沙尘及其随赤道东风向西输送使得沙尘气溶胶成为非洲沙漠地区和紧邻的大西洋海区的主要气溶胶组分;AOD高值区和沙尘气溶胶光学厚度高值区在1—7月随赤道辐合带北移同步向北移动,而在8—12月则向南回撤。2）刚果盆地大气气溶胶主要为热带雨林和稀树草原排放的有机碳（OC）和黑碳（BC）气溶胶;其中与生物质燃烧源排放有关的OC、BC高值主要集中在干季（6—9月）的后半段（8—9月）;而生物源OC排放全年连续,其排放峰值出现于雨季开始时;生物质燃烧排放高值期与生物源排放高值期前后相继,形成干季（尤其是后半段）时期的OC、BC光学厚度高值。3）亚马逊河入海口地区主要气溶胶组分为海盐气溶胶,9—11月该区风力输送增强,风向由东南风转变为东风,海盐进入亚马逊河入海口处,形成AOD和海盐气溶胶光学厚度高值区。4）撒哈拉沙漠沙尘气溶胶向大西洋传输的偏北月份为7—9月、偏南月份为1—3月;2000—2016年海区沙尘气溶胶的传输路径存在向南移动的变化趋势,与同期亚速尔高压的增强和沙尘传输路径以北北风分量的增强以及赤道辐合带的移动一致。上述研究结果揭示了利用大气气溶胶时空变化特征反映区域大气环流和气候变化的可能性。     

Synergistic use of AIRS and MODIS for dust top height retrieval over land

It is nontrivial to extract the dust top height(DTH) accurately from passive instruments over land due to the complexity of the surface conditions. The Moderate Resolution Imaging Spectroradiometer(MODIS) deep blue(DB) algorithm can be used to infer the aerosol optical depth(AOD) over high-reflective surfaces. The Atmospheric Infrared Sounder(AIRS) can simultaneously obtain the DTH and optical depth information. This study focuses on the synergistic use of AIRS observations and MODIS DB results for improving the DTH by using a stable relationship between the AIRS infrared and MODIS DB AODs. A one-dimensional variational(1DVAR) algorithm is applied to extract the DTH from AIRS. Simulation experiments indicate that when the uncertainty of the dust optical depth decreases from 50% to 20%, the improvement of the DTH retrieval accuracy from AIRS reaches 200 m for most of the assumed dust conditions. For two cases over the Taklimakan Desert, the results are compared against Cloud-Aerosol Lidar with Orthogonal Polarization(CALIOP) measurements. The results confirm that the MODIS DB product could help extract the DTH over land from AIRS.     

使用物理方法反演中国陆地雨强和水凝物垂直结构

使用MM5模式模拟了11个降水个例,获得中国陆地的降水廓线,由蒙特卡罗辐射传输模式计算其上行辐射亮温,构成初始云一辐射数据库.采用对照表方法从中获得Db_ml和Db_m2两个数据集,作为GPROF反演算法的先验数据集.对2007年7月的3次强降水过程的地面雨强进行反演,与微波成像仪(TMI)及NESDIS、GSCAT、...     

Aerosol optical thickness retrieval over non-Lambertian land surface with synergistic use of AATSR radiance measurements and MODIS derived Albedo Model Parameters

Various algorithms have recently been developed in order to retrieve the aerosol optical thickness (AOT) at continental scales. However, they are, to some extent, subject to large uncertainties resulting from some necessary physical assumptions on land surface anisotropy and level of brightness. In fact, disentangling aerosol and surface signals contained in the top of atmosphere (TOA) radiance received at the satellite level are a matter of difficulty because a single sensor itself cannot gather all required spatial, temporal, spectral and angular information. In particular, each instrument yields limited scanning configuration due to its platform's orbital characteristics. In this regard, a synergetic approach is presented which merges Advanced Along-Track Scanning Radiometer (AATSR) TOA radiances and the MODerate resolution Imaging Spectroradiometer (MODIS) Bi-directional Reflectance Distribution Function (BRDF)/Albedo Model Parameters Product for the retrieval of AOT at 0.55, 0.66, and 0.87 µm wavelengths over non-Lambertian land surface at a 5 km spatial resolution. In this approach, BRDF products serve to assess the surface reflectance in the AATSR geometry as a boundary layer. The peculiarity of the approach is that no specific assumption is required about the spectral characteristics of land surface, thus allowing for a quantitative retrieval of aerosol particles over any arbitrary land unit in virtue of combining forward and nadir AATSR observations. We obtain on average differences within 0.1τ compared to in situ AErosol RObotic NETwork (AERONET) measurements and 36 retrievals corresponding to 27 January, 12 February, 16 March, 28 May, 26 June, and 21 July 2006, respectively, over the city of Beijing in China. Pearson's correlation coefficient is 0.94 and 0.96 for nadir and forward AATSR, respectively. These suggest that AOT retrieval over land is indeed feasible by taking benefit of the validated MODIS BRDF. Besides, the first results indicate that the AATSR retrievals might be used to evaluate the spectral behaviour of the AOT.     

FY-3A/MERSI、MODIS C5.1和C6气溶胶光学厚度产品在中国区域与地面观测站点的对比分析

准确获取气溶胶光学厚度对于气候变化研究和大气环境监测具有重要意义。通过波长插值和时空匹配方法,利用气溶胶自动观测站网（AERONET）观测的气溶胶光学厚度（AOD）对风云3A/中分辨率光谱成像仪（FY-3A/MERSI）、Terra（Aqua）/MODIS的C5.1（Collections 5.1）和C6（Collections 6）气溶胶光学厚度产品在中国区域的反演精度进行验证分析。结合一次发生在中国境内的沙尘天气与一次严重雾霾天气个例,分析上述卫星气溶胶光学厚度的分布特征。研究结果表明,（1）FY-3A/MERSI AOD的反演精度较高（R=0.887,RMSE=0.234）,其值低于AERONET的观测值（Bias=-0.293）。（2）在不同的下垫面下,各种卫星暗像元算法AOD产品反演精度有差异,植被覆盖情况越好,反演精度越高,而植被很少的地区,即亮地表甚至没有反演值。（3）MODIS C5.1深蓝算法产品能在亮地表地区反演AOD,但效果不佳。MODIS C6中的深蓝算法产品在不同下垫面的反演精度都很高（RMSE为0.096-0.127）。（4）在不同季节的对比中,各种卫星AOD产品在夏季的反演精度最差,而反演最好的季节各有不同。（5）在一次沙尘天气污染与一次严重雾霾天气个例中,中国西部与北部区域,MODIS C6深蓝算法AOD的监测效果优于其他算法AOD;MERSI AOD产品在此区域的分布不连续。总体而言,MODIS C6 AOD分布比MODIS C5.1产品连续,MODIS 3 km产品在相同区域的AOD值高于其他产品。以上结论可为卫星AOD产品在中国区域的使用提供参考。      

星载双频云雷达的云微物理参数反演算法研究

使用星载雷达模拟器输出的模拟数据,为星载双频云雷达选择了最佳的频点组合,并开展了双频联合反演云微物理参数的算法研究。结果表明:（1）在位于大气窗口的6组频点组合中,94/220 GHz的组合对滴谱参数的微小变化较为敏感,有利于进行双频的联合反演。综合考虑不同频点的探测能力、衰减以及工业部门的制造水平后,认为94/220 GHz可以作为未来星载双频测云雷达的探测频点。（2）双频反演中最核心的双波长比（DWR）和体积中值直径（D₀）的关系与冰晶粒子密度相关。当密度随着粒子直径变化时,DWR随着D₀单调递增,当粒子密度固定不变时,DWR-D₀曲线可能会出现非单调变化,从而使得固定密度时的反演比变密度时更加复杂。（3）后向迭代的双频反演算法同样适用于94/220 GHz进行云微物理参数的反演,并且对模拟数据的反演精度较高。此外,反演精度受到系统噪声以及定标精度的影响,为了满足反演精度的要求,系统噪声和定标误差应该控制在1 dBz以内。      

A simple model for air/snow fractionation of aerosol components over the Antarctic Peninsula

A model has been set up to investigate the wet and dry aerosol removal processes which occur in clean air over the Antarctic Peninsula. Input for the model was obtained from bulk chemical analysis and scanning electron microscopy of aerosol and snow samples collected simultaneously at remote sites around the Peninsula. The model predicts that sulphate and sea-salt aerosol will be removed mainly in-cloud by riming of falling snow and ice crystals. Crustal aerosol is principally removed by acting as nuclei for these crystals and by impaction on falling snow. For the largest, locally-generated aerosol dry deposition is indicated as the major removal process. These findings suggest a possible mechanism for the observed air/snow fractionation.     

A differential optical absorption spectroscopy method for {X_{CO_2}} retrieval from ground-based Fourier transform spectrometers measurements of the direct solar beam

A differential optical absorption spectroscopy (DOAS)-like algorithm is developed to retrieve the column-averaged dry-air mole fraction of carbon dioxide from ground-based hyper-spectral measurements of the direct solar beam. Different to the spectral fitting method, which minimizes the difference between the observed and simulated spectra, the ratios of multiple channel-pairs——one weak and one strong absorption channel——are used to retrieve X CO2 from measurements of the shortwave infrared (SWIR) band. Based on sensitivity tests, a super channel-pair is carefully selected to reduce the effects of solar lines, water vapor, air temperature, pressure, instrument noise, and frequency shift on retrieval errors. The new algorithm reduces computational cost and the retrievals are less sensitive to temperature and H2O uncertainty than the spectral fitting method. Multi-day Total Carbon Column Observing Network (TCCON) measurements under clear-sky conditions at two sites (Tsukuba and Bremen) are used to derive X CO2 for the algorithm evaluation and validation. The DOAS-like results agree very well with those of the TCCON algorithm after correction of an airmass-dependent bias.