青藏高原是世界上最大的高、低纬度多年冻土带，近几十年来，其多年冻土带迅速退化，其最显著的特征之一就是热融湖塘的形成。这样的湖泊由于能够调节碳循环、水和能量通量而引起了极大的关注。然而，这一地区的热融湖塘的分布在很大程度上仍不为人所知，这阻碍了我们对多年冻土的响应及其碳反馈对气候变化的理解。本数据集基于200余景Sentinel-2A影像，结合ArcGIS、NDWI和Google Earth Engine平台，通过GEE自动提取和人工目视解译的方法提提取青藏高原多年冻土区内热融湖塘边界。在2018年热融湖塘数据集中，青藏高原多年冻土区共有121,758个热融湖塘，面积为0.00035-0.5 km²，总面积为1730 km² 。本次热融湖塘编目数据集为青藏高原水资源评价、多年冻土退化评价、热喀斯特研究提供了基础数据。
陈旭, 牟翠翠, 贾麟, 李志龙, 范成彦, 母梅, 彭小清, 吴晓东
Snow is a significant component of the ecosystem and water resources in high-mountain Asia (HMA). Therefore, accurate, continuous, and long-term snow monitoring is indispensable for the water resources management and economic development. The present study improves the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra and Aqua satellites 8 d (“d” denotes “day”) composite snow cover Collection 6 (C6) products, named MOD10A2.006 (Terra) and MYD10A2.006 (Aqua), for HMA with a multistep approach. The primary purpose of this study was to reduce uncertainty in the Terra–Aqua MODIS snow cover products and generate a combined snow cover product. For reducing underestimation mainly caused by cloud cover, we used seasonal, temporal, and spatial filters. For reducing overestimation caused by MODIS sensors, we combined Terra and Aqua MODIS snow cover products, considering snow only if a pixel represents snow in both the products; otherwise it is classified as no snow, unlike some previous studies which consider snow if any of the Terra or Aqua product identifies snow. Our methodology generates a new product which removes a significant amount of uncertainty in Terra and Aqua MODIS 8 d composite C6 products comprising 46 % overestimation and 3.66 % underestimation, mainly caused by sensor limitations and cloud cover, respectively. The results were validated using Landsat 8 data, both for winter and summer at 20 well-distributed sites in the study area. Our validated adopted methodology improved accuracy by 10 % on average, compared to Landsat data. The final product covers the period from 2002 to 2018, comprising a combination of snow and glaciers created by merging Randolph Glacier Inventory version 6.0 (RGI 6.0) separated as debris-covered and debris-free with the final snow product MOYDGL06*. We have processed approximately 746 images of both Terra and Aqua MODIS snow containing approximately 100 000 satellite individual images. Furthermore, this product can serve as a valuable input dataset for hydrological and glaciological modelling to assess the melt contribution of snow-covered areas. The data, which can be used in various climatological and water-related studies, are available for end users at https://doi.org/10.1594/PANGAEA.901821 (Muhammad and Thapa, 2019).
Sher Muhammad
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