Monitoring snow cover variability in an agropastoral area in the Trans Himalayan region of Nepal using MODIS data with improved cloud removal methodology
Monitoring snow cover variability in an agropastoral area in the Trans Himalayan region of Nepal using MODIS data with improved cloud removal methodology
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DOI：
10.1016/j.rse.2011.01.006
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发表时间：
2011-05
影响因子：
13.5
通讯作者：
K. Paudel;Peter Andersen
中科院分区：
文献类型：
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作者：
K. Paudel;Peter Andersen
监测干燥高海拔跨喜马拉雅地区 (THR) 的积雪范围和模式对于了解持续气候变化和变异对当地和区域的影响具有重要意义。免费提供的中分辨率成像光谱仪（MODIS）积雪图像具有 500 m 的空间和日时间分辨率，可为区域积雪测绘、监测和水文建模提供基础。然而，高云遮蔽仍然是主要限制。在这项研究中，我们提出了一个五个连续步骤的方法——结合来自 Terra 和 Aqua 卫星的数据；相邻时间演绎；基于正交相邻像素的空间滤波；基于区域雪线方法的空间过滤；以及基于纬向雪循环的时间过滤——消除 MODIS 每日雪产品中的云遮挡。这项研究还研究了过去十年尼泊尔 THR 地区积雪的时空变化。由于该地区没有测量积雪数据的地面站，因此通过将云量最少的原始 MODIS 积雪数据与云生成的 MODIS 积雪数据（由另一种密集云覆盖产品的云填充）进行比较来评估所提出方法的性能。分析表明，所提出的五步方法在云减少方面是有效的（平均准确率> 91％）。结果显示，过去十年平均积雪、最大积雪范围和积雪持续时间的年际和季节内变化非常大。峰雪期每年推迟约6.7天，近十年来该地区主要农牧业产区积雪持续时间显着减少。
Monitoring the extent and pattern of snow cover in the dry, high altitude, Trans Himalayan region (THR) is significant to understand the local and regional impact of ongoing climate change and variability. The freely available Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover images, with 500m spatial and daily temporal resolution, can provide a basis for regional snow cover mapping, monitoring and hydrological modelling. However, high cloud obscuration remains the main limitation. In this study, we propose a five successive step approach — combining data from the Terra and Aqua satellites; adjacent temporal deduction; spatial filtering based on orthogonal neighbouring pixels; spatial filtering based on a zonal snowline approach; and temporal filtering based on zonal snow cycle — to remove cloud obscuration from MODIS daily snow products. This study also examines the spatial and temporal variability of snow cover in the THR of Nepal in the last decade. Since no ground stations measuring snow data are available in the region, the performance of the proposed methodology is evaluated by comparing the original MODIS snow cover data with least cloud cover against cloud-generated MODIS snow cover data, filled by clouds of another densely cloud-covered product. The analysis indicates that the proposed five-step method is efficient in cloud reduction (with average accuracy of >91%). The results show very high interannual and intra-seasonal variability of average snow cover, maximum snow extent and snow cover duration over the last decade. The peak snow period has been delayed by about 6.7days per year and the main agropastoral production areas of the region were found to experience a significant decline in snow cover duration during the last decade.