基于沙尘气溶胶识别的中国北方地区MODIS云检测产品的改进研究

THE STUDY ON THE IMPROVEMENT OF CLOUD MASK PRODUCT OF MODIS BASED ON THE DETECTION OF DUST AEROSOLS IN NORTHERN CHINA

美国国家航空航天局(NASA)的MODIS业务云检测产品MOD35是其他大气产品和陆地产品反演的辅助数据,也是目前很多云检测研究的检验依据。为研究MODIS云检测业务产品MOD35的监测效果,分析了中国北方地区有沙尘暴天气的MOD35产品,发现产品易将沙尘气溶胶区域误判为云。为了区分沙尘和云,对中国北方地区白天4次沙尘过程数据进行散点图分析,并通过计算损失率得到沙尘气溶胶的11μm、12μm通道亮温差特征和11μm通道、3.7μm通道的亮温范围,改进了MODIS监测沙尘气溶胶的算法。应用此算法对MODIS云检测产品中的沙尘气溶胶污染进行判别,分析结果与国家气象卫星中心发布的沙尘监测一致。改进的算法能有效地监测出MOD35产品中误判为云的沙尘区域,结合MOD35自身的厚气溶胶标记,改进了云检测产品的效果。

The operational cloud mask product of NASA named MOD35 is not only the primary ancillary input to other products for the atmosphere and land surface,but also the main criteria in the study of cloud detection at present.In order to evaluate the MOD35,the products that contain dust storms in northern China are studied in this paper.The cases show that some dust aerosols are misclassified as clouds in the MOD35.Based on the scatter diagram analysis of four daytime dust storms in northern China,the brightness temperature difference of thermal infrared bands（11 μm and 12 μm） and the brightness temperature range of these bands are obtained by calculating the loss rate,resulting in the improvement of the algorithm for detection of dust aerosols with the MODIS data.As the results of the improved algorithm are consistent with the dust products distributed by China Meteorological Administration,it is applied to distinguish the dusts that have been misclassified as clouds in MOD35 product and then to correct the MODIS cloud mask product combining the heavy aerosol signs in MOD35 itself.