Large-scale observations of alpine snow and ice cover in Asia: Using multi-temporal VEGETATION sensor data

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Abstract
In this study we used twenty-five 10-day synthetic products (composites) of the VEGETATION (VGT) sensor on SPOT 4 satellite from 11-20 March 1999 to 11-20 November 1999 to map snow and ice cover at 1-km spatial resolution in an alpine environment of Asia. The study area is within 73°-103° E and 25°-40° N (a total land area of 4.7 million km 2 ), and includes the highest alpine region in the world (e.g. Himalaya Mountains, Qinghai-Tibet Plateau, Pamirs Plateau, Karakoram Range). In the VGT-based mapping approach, the Normalized Difference Snow/Ice Index (NDSII) is calculated as NDSII=(B2-MIR)/(B2+MIR), where the ground reflectance values of the red band (VGT band B2) and the mid-infrared band (VGT band MIR) are used. When NDSII and the reflectance value of the near-infrared band (VGT band B3) in a pixel (1 km 2 1 km) meet the thresholds of NDSII S 0.40 and band B3>0.11, the pixel is assigned to be snow/ice cover. Total areas of snow/ice cover in 2 the alpine region had large seasonal variations, ranging from 0.46 million km in 11-20 March 1999 to 0.05 million km 2 in 1-10 August 1999 to 0.60 million km 2 in 11-20 November 1999. Spatial distributions of snow/ice cover also varied substantially across the alpine region. There were large areas of snow/ice cover in the north-western part of the alpine region in March and April, but large areas of snow/ice cover in the eastern part of the alpine region in October and November. Qualitatively, spatial patterns and temporal dynamics of snow/ice cover in the alpine region are closely correlated to the plateau monsoon climate and its precipitation patterns.