Cloud Removal Methodology From MODIS Snow Products In Alpine Areas With Complex Topography

MODIS snow cover area(SCA)maps have been widely used to investigate snow coverage changes because of their higher spatio-temporal resolution and snow/cloud discrimination capabilities.However,cloud obscurtion hinders their extensive application,especially in mountain regions.In Alpine areas with complex topography,spatial local heterogeneity is relatively higher and the distribution of snow and no snow(land)is discontinuous and scattered,resulting in weak spatial autocorrelation.Meanwhile,in Alpine area,cloud coverage in original MODIS SCA data is usually continuous and persistent,especially in winter.Moreover,snowpack located at the transient zones in Alpine area is extremely unstable and has several snow/land cycles during a hydrologic year.Aimed at above problems,daily combination of Terra and Aqua,Temporal Moving Average(TMA)deduction,extreme snow-line method and K-Nearest Neighbor(KNN)algorithm were used in this study to remove clouds in MODIS SCA data in Alpine areas with complex topography and then yield cloud-free MODIS SCA data.Temporal moving average deduction can have both higher accuracy and better performance of cloud removal.The extreme snow-line method is used for removing persistent cloud coverage at very low and very high altitude.K-Nearest Neighbor algorithm makes use of spatial information with unchanged weight and temporal information with greater weight simultaneously to eliminate clouds located at the transient zones in Alpine area.Two methods consisting of cloud-filled validation and no-filled validation were used to assess the cloud removal methodology developed in this study and the overall accuracy of the methodology was 92.11% and 83.12%,respectively.Moreover,our methodology had the best performance and the highest accuracy as compared with other three cloud removal procedures.Therefore,the solution proposed in this study can effectively and reasonably eliminate clouds fromMODIS SCA products in Alpine areas with complex topography.