ESA Snow Climate Change Initiative (Snow_cci): Daily global Snow Cover Fraction - viewable (SCFV) from AVHRR (1982 - 2019), version 1.0

This dataset contains Daily Snow Cover Fraction of viewable snow from AVHRR, produced by the Snow project of the ESA Climate Change Initiative programme. Snow cover fraction viewable (SCFV) indicates the area of snow viewable from space over land surfaces. In forested areas this refers to snow viewable on top of the forest canopy. The SCFV is given in percentage (%) per pixel. The global SCFV 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 SCFV time series provides daily products for the period 1982-2019. 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 SCFV 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 630 nm and 1.61 µm (channel 3a or the reflective part of channel 3b), and an emissive band centred at about 10.8 µm. The snow_cci snow cover mapping algorithm is a two-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 SCFV retrieval method is applied. The following auxiliary data set is used for product generation: 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. The SCFV product is aimed to serve the needs for users working in the 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 SCFV product development and generation. ENVEO developed and prepared all auxiliary data sets used for the product generation. The SCFV 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 38 years.

本数据集包含由欧洲空间局（ESA）气候变化倡议计划雪项目生成的、基于先进甚高分辨率辐射计（Advanced Very High Resolution Radiometer, AVHRR）观测的可视积雪每日积雪覆盖率数据。可视积雪覆盖率（Snow Cover Fraction Viewable, SCFV）指地表上空从太空观测到的可视积雪区域占比；在林区，该指标对应林冠层上方的可视积雪。SCFV以百分比（%）为单位，按单个像素给出。全球SCFV产品的像素分辨率约为5千米，覆盖除南极冰盖与格陵兰冰盖外的所有陆地区域，包含格陵兰沿海地带。其时间序列为1982年至2019年的每日产品。该产品基于中等分辨率光学卫星数据，数据源为AVHRR。云掩膜处理采用气候变化倡议云产品v3.0版（Cloud CCI cloud v3.0 mask）。基于Metsämäki等人（2015）提出的ESA GlobSnow方法，并新增预分类模块，研究人员对AVHRR数据的雪_cci（snow_cci）SCFV反演方法进行了进一步优化完善。所有无云像素均用于积雪范围制图，所用光谱波段包括中心波长约630纳米和1.61微米的波段（即3a通道或3b通道的反射部分），以及中心波长约10.8微米的发射波段。雪_cci积雪覆盖制图算法采用两步法：首先通过严格的预分类识别所有确定无雪的无云像素；对于剩余像素，则应用雪_cci SCFV反演方法。产品生成所用的辅助数据集包括2000年ESA CCI土地覆盖数据；基于该数据集对水体、永久积雪与冰区进行掩膜处理：当某像素超过50%的区域被归类为水体时，对该像素进行水体掩膜；当聚合后的地图中某像素超过50%被识别为永久积雪与冰区时，同样对其进行掩膜处理。两类辅助数据均被单独聚合至SCFV产品的像素分辨率。SCFV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、气候模拟，以及水文学、气象学与生物学相关研究方向。本SCFV产品的开发与生成由伯尔尼大学遥感研究小组负责；ENVEO公司负责产品生成所用全部辅助数据集的开发与预处理。本AVHRR版SCFV产品存在一处持续92天的较长数据间隙（1994年11月至1995年1月），以及16处单日数据间隙，在整个38年研究周期内的数据覆盖率达99%。