基于规则的MODIS数据日间云检测与比较分析

Comparison and Daytime Cloud Detection from MODIS Data Using a Threshold Rule Based Approach

针对我国西北地区下垫面光谱特性及MODIS通道特点,提出一种基于阈值规则的日间云检测算法,旨在克服目前云检测工作中普遍存在的分离薄云与高反射率晴空地表、识别体积较小的云体、识别冰雪上空云像元等方面的困难。采用2008年两期Terra星MODIS数据进行云检测试验,并将这种算法得到的云检测结果与MOD35-2L云掩膜产品进行比较分析。结果表明,这种算法可有效检测出我国西北地区日间各种类型的云,且在此类地区该算法对面积小、形状破碎的云及冰雪上空云像元的检测效果优于MOD35-2L云掩膜产品。因此,这种算法适用于干旱/半干旱地区的云检测,并可应用于MODIS数据的预处理环节中。

Considering the spectral properties of land covers in the northwest China and the characteristics of the channels of the Moderate Resolution Imaging Spectroradiometer （MODIS）, based on a group of threshold rules, this study proposed a daytime cloud detection algorithm to overcome common difficulties of current cloud detection studies in separating thin cloud covers from clean sky when surface reflectance was high, and in identifying small-area cloud covers and those cloud pixels above ice-snow covers. Cloud detection experiments were conducted on the two dates MODIS data from the Terra Earth Observing System in 2008. The result shows that all kinds of cloud cover in the study area can he well detected using the proposed algorithm. Comparing with the MOD35 2L cloud mask product, this approach can better identify small-area and irregular-shaped cloud covers and the cloud pixels above the ice-snow covers than the MOD35. 2L product. Thus, the proposed approach is efficient for.daytime cloud detection in arid and semi-arid areas and useful for the preprocessing of MODIS data.