ESA Snow Climate Change Initiative (Snow_cci): Daily global Snow Cover Fraction - snow on ground (SCFG) from AVHRR (1982 - 2018), version 2.0

This dataset contains Daily Snow Cover Fraction (snow on ground) from AVHRR, produced by the Snow project of the ESA Climate Change Initiative programme. Snow cover fraction on ground (SCFG) indicates the area of snow observed from space over land surfaces, in forested areas corrected for the transmissivity of the forest canopy. The SCFG is given in percentage (%) per pixel. The global SCFG product is available at about 5 km pixel size for all land areas, excluding Antarctica and Greenland ice sheets. The coastal zones of Greenland are included. The SCFG time series provides daily products for the period 1982-2018. The product is based on medium resolution optical satellite data from the Advanced Very High Resolution Radiometer (AVHRR). Clouds are masked using the Cloud CCI cloud v3.0 mask product. The retrieval method of the snow_cci SCFG product from AVHRR data has been further developed and improved based on the ESA GlobSnow approach described by Metsämäki et al. (2015) and complemented with a pre-classification module. All cloud free pixels are then used for the snow extent mapping, using spectral bands centred at about 0.63 µm and 1.61 µm (channel 3a or the reflective part of channel 3b (ref3b)), and an emissive band centred at about 10.8 µm. The snow_cci snow cover mapping algorithm is a three-step approach: first, a strict pre-classification is applied to identify all cloud free pixels which are certainly snow free. For all remaining pixels, the snow_cci SCFG retrieval method is applied. Finally, a post-processing removes erroneous snow pixels caused either by falsely classified clouds in the tropics or by unreliable ref3b values at a global scale. The following auxiliary data sets are used for product generation: i) ESA CCI Land Cover from 2000; water bodies and permanent snow and ice areas are masked based on this dataset. Both classes were separately aggregated to the pixel spacing of the SCF product. Water areas are masked if more than 50 percent of the pixel is classified as water, permanent snow and ice areas are masked if more than 50 percent are identified as such areas in the aggregated map; ii) Forest canopy transmissivity map; this layer is based on the tree cover classes of the ESA CCI Land Cover 2000 data set and the tree cover density map from Landsat data for the year 2000 (Hansen et al., Science, 2013, DOI: 10.1126/science.1244693). This layer is used to apply a forest canopy correction and estimate in forested areas the fractional snow cover on ground. The SCFG product is aimed to serve the needs of users working in cryosphere and climate research and monitoring activities, including the detection of variability and trends, climate modelling and aspects of hydrology, meteorology, and biology. The Remote Sensing Research Group of the University of Bern is responsible for the SCFG product development and generation. ENVEO developed and prepared all auxiliary data sets used for the product generation. The SCFG AVHRR product comprises one longer data gap of 92 between November 1994 and January 1995, and 16 individual daily gaps, resulting in a 99% data coverage over the entire study period of 37 years.

本数据集包含源自高级甚高分辨率辐射计（Advanced Very High Resolution Radiometer, AVHRR）的每日地面积雪覆盖分数（Snow Cover Fraction on Ground, SCFG），由欧洲空间局（European Space Agency, ESA）气候变化倡议计划的积雪项目生成。地面积雪覆盖分数（SCFG）指通过太空观测得到的陆面积雪面积，在林区已针对林冠透射率完成校正。SCFG以百分比（%）为单位，按单个像素给出。全球SCFG产品的像素分辨率约为5 km，覆盖除南极洲与格陵兰冰盖之外的所有陆地区域，格陵兰沿海区域则被纳入覆盖范围。该SCFG时间序列提供了1982年至2018年期间的每日产品，其数据基础为高级甚高分辨率辐射计（AVHRR）的中分辨率光学卫星观测数据。云掩膜处理采用欧洲空间局云气候变化倡议（Cloud CCI）的v3.0版云掩膜产品实现。针对AVHRR数据的snow_cci SCFG产品反演方法，依托Metsämäki等（2015）提出的ESA GlobSnow方案进行了迭代开发与优化，并补充了预分类模块。随后，所有无云像素将被用于积雪范围制图，所用光谱波段包括中心波长约0.63 µm与1.61 µm的波段（即3a波段，或3b波段的反射分量ref3b），以及中心波长约10.8 µm的发射波段。snow_cci积雪覆盖制图算法采用三步流程：首先执行严格的预分类，以识别所有确认为无雪的无云像素；对于剩余像素，则应用snow_cci SCFG反演方法；最后通过后处理步骤剔除两类错误积雪像素：一类是热带区域被误分类的云所导致的错误积雪像素，另一类是全球范围内不可靠的ref3b值所引发的错误积雪像素。产品生成过程中用到以下辅助数据集：i) 2000年版ESA CCI土地覆盖数据集：基于该数据集对水体及永久积雪冰盖区域进行掩膜。将这两类区域分别聚合至SCFG产品的像素分辨率后，若某像素中超过50%的区域被归类为水体，则对该像素执行水体掩膜；若聚合后的地图中超过50%的区域被识别为永久积雪冰盖，则对该像素执行永久积雪冰盖掩膜。ii) 林冠透射率图层：该图层基于2000年版ESA CCI土地覆盖数据集的树木覆盖分类，以及2000年Landsat数据的树木覆盖密度图（Hansen et al., Science, 2013, 数字对象标识符（Digital Object Identifier, DOI）: 10.1126/science.1244693）生成。该图层用于执行林冠校正，以估算林区的地面积雪覆盖分数。SCFG产品旨在满足冰冻圈与气候研究、监测相关用户的需求，涵盖变异性与趋势检测、气候建模，以及水文学、气象学与生物学相关研究方向。伯尔尼大学遥感研究组负责SCFG产品的开发与生成工作，ENVEO公司则负责产品生成所需全部辅助数据集的开发与制备。该AVHRR版SCFG产品存在一处长达92天的较长数据间隙，覆盖1994年11月至1995年1月，另有16处单日数据间隙；在1982至2018年这37年的完整研究周期内，整体数据覆盖率可达99%。

搜集汇总

背景与挑战

背景概述

该数据集包含1982年至2018年全球每日雪覆盖分数（SCFG）数据，基于AVHRR卫星数据生成，空间分辨率约为5公里，适用于气候研究和雪覆盖变化监测。