Mukherjee Nikita Roy, Krishna A P
Department of Remote Sensing, Birla Institute of Technology, Mesra, Jharkhand, 835215, India.
Environ Monit Assess. 2023 Apr 26;195(5):611. doi: 10.1007/s10661-023-11139-3.
This study assessed the snow/ice surface area changes over the Zemu Glacier in the Eastern Himalayas. Zemu is considered to be the largest glacier in the Eastern Himalayas located in the Sikkim State of India. Change detection in the snow/ice surface areal extent of the Zemu Glacier was delineated from the year 1945 using US Army Map Service-Topographical Sheets and Landsat imageries available from 1987 to 2020. The results obtained solely focus on surface-change delineation using remote sensing satellite data and GIS software. Landsat imagery of the years 1987, 1997, 2009, 2018, and 2020 was used for snow and ice pixel extraction. Normalized Difference Snow Index (NDSI), Snow Cover Index (S3), and new band ratio index were used to extract the pure snow and ice pixels, fresh snow, and debris-covered snow/ice area and pixels mixed with shadow to demarcate the surface area changes. Manual delineation was required and undertaken for better results. A slope raster image was generated from Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) data to delineate the slope and hill shade. The results illustrate that the snow/ice surface covering the glacier had an area of 113.5 km in the year 1945 which was reduced to 78.31 km in the year 2020 indicating a total snow/ice surface area loss of 31% in 75 years. A loss of 11.45% was observed from 1945 to 1987 in the areal extent, while from 1987 to 2009, a decadal loss of approximately 7% was observed. The surface area loss of 8.46% from 2009 to 2018 led to infer the maximum loss of snow and ice over the glacier body at a rate of 0.94% per year. Between the years 2018 and 2020, the glacier lost 1.08% of its surface area. The Accumulation Area Ratio (AAR) considering the accumulation and ablation areas of the glacier indicated a gradual decline of the accumulation zone in the recent years. Global Land Ice Measurement from Space (GLIMS) program data with RGI version 6.0 was used as a reference to demarcate the areal extent of Zemu Glacier. The study gained above 80% of overall accuracy by generating a confusion matrix in ArcMap. The analysis of this seasonal snow/ice cover showed that there has been a drastic decline in the surface snow/ice cover area over the Zemu Glacier over the years 1987 to 2020 and NDSI; S3 analysis provided improved results to delineate snow/ice cover area over such steep terrain topography of Sikkim Himalaya.
本研究评估了东喜马拉雅地区则普冰川的冰雪表面积变化。则普冰川被认为是位于印度锡金邦的东喜马拉雅地区最大的冰川。利用美国陆军地图服务局的地形图以及1987年至2020年的陆地卫星影像，对则普冰川1945年以来的冰雪表面积范围进行了变化检测。所获结果仅聚焦于利用遥感卫星数据和地理信息系统软件进行地表变化描绘。使用了1987年、1997年、2009年、2018年和2020年的陆地卫星影像来提取冰雪像素。利用归一化差异雪指数（NDSI）、积雪指数（S3）和新的波段比率指数来提取纯冰雪像素、新雪、碎屑覆盖的冰雪区域以及与阴影混合的像素，以划定表面积变化。为获得更好的结果，需要并进行了人工描绘。利用航天飞机雷达地形测绘任务（SRTM）数字高程模型（DEM）数据生成了坡度栅格图像，以描绘坡度和山体阴影。结果表明，1945年覆盖该冰川的冰雪表面积为113.5平方千米，到2020年减少至78.31平方千米，表明75年间冰雪表面积总共损失了31%。1945年至1987年期间，面积范围损失了11.45%，而1987年至2009年期间，十年间损失约7%。2009年至2018年表面积损失8.46%，由此推断冰川主体上的冰雪损失最大，年损失率为0.94%。2018年至2020年期间，该冰川损失了1.08%的表面积。考虑到冰川的积累区和消融区的积累面积比率（AAR）表明，近年来积累区在逐渐缩小。使用全球陆地冰面卫星测量（GLIMS）计划数据和RGI 6.0版本来划定则普冰川的面积范围。通过在ArcMap中生成混淆矩阵，该研究获得了80%以上的总体准确率。对这种季节性冰雪覆盖的分析表明，1987年至2020年期间，则普冰川的地表冰雪覆盖面积急剧下降，且NDSI；S3分析为描绘锡金喜马拉雅这种陡峭地形上的冰雪覆盖面积提供了更好的结果。
