MODIS气溶胶光学厚度在长江三角洲地区适用性分析

Validation of Modis Aerosol Optical Thickness Retrieval Over Yangtze Delta Region of China

利用太湖、浙江林学院和千岛湖站点AERONET数据对MODIS气溶胶光学厚度适用性进行验证表明,长江三角洲地区MODIS气溶胶光学厚度反演精度具有较大的地域差异,太湖站点显著偏高,达到MODIS精度设计范围(±0.05±0.15τ)的数据仅占30.0%左右,不具有显著适用性,地表反射率估计不足是造成太湖MODIS反演误差的主要原因。浙江林学院站点整体偏低,AQUA/MODIS和TERRA/MODIS主要误差分别来源于对气溶胶单次散射反照率和对地表反射率的估计不足,两颗卫星分别有81.8%和53.3%的数据满足MODIS设计精度,具有较好的适用性。千岛湖站点MODIS/AOT显著偏低,MODIS极大地高估了气溶胶单次散射反照率,然而缺乏2.0级数据对其进行有力的验证。目前,长江三角洲地区MODIS产品存在较大的误差订正空间,对气溶胶模式进行进一步的精细划分以及根据具体的地表状况拓展更准确的卫星反演算法,是MODIS产品广泛应用的必要前提。

This paper presents a comparison of aerosol optical thickness（AOT） retrieved from MODIS（both terra and aqua） collections with in situ ground-based data at three Aerosol Robotic Network（AERONET） sites over Yangtze Delta region from 2007 to 2009.The validation results show that the performances of the MODIS AOT retrievals have significant regional differences.MODIS is found to overestimate AOT observably at Taihu site,with only about 30% of retrieval data falling within the expected uncertainty.The systematic biases are mainly due to incorrect assumptions in the surface reflectance.There is a poor MODIS retrieval in this region.On the other hand,AQUA and TERRA MODIS derived AOTs are negatively biased at Zhejiang Forestry University（ZFU） site with 81.8% and 53.3% of retrieval data falling in the expected uncertainty,and the dominant sources of MODIS aerosol retrieval errors are aerosol models and surface reflectance estimations,respectively.The MODIS algorithm can deal well with this area.For Qiandaohu site,the MODIS data are significantly underestimated due to the overestimation of aerosol single scattering albedo.Unfortunately,there is no sufficient level 2.0 AERONET data to take a more reliable validation at this site.The analysis in this paper indicates the need for systematic modification of the MODIS algorithm over Yangtze delta region of China.