The dataset provides daily snow cover grid maps for the territory of Austria in the period 2000-2020. The dataset consists of two products based on observations from Terra (in the period 2000-2020) and Aqua (period 2002-2020) satellites, both using Moderate Resolution Imaging Spectroradiometer (MODIS) data. The spatial resolution of all maps is 500m.  The snow cover maps for Austria are processed from MODIS, Version 006, MOD10A1 (Terra, Hall and Riggs, 2016) and MYD10A1 (Aqua, Hall and Riggs, 2016) products. These products provide daily global grid maps of a Normalized Difference Snow Index (NDSI), which represents a difference in reflectance observations in the visible and infrared MODIS bands (band 4 and band 6). Snow cover classification requires then attributing the NDSI values to snow or land classes. The dataset uses for the snow cover classification a method developed and introduced in Tong et al. (2020). In comparison, previous approaches used a spatially and temporally fixed NDSI (i.e. if the NDSI value for a pixel was larger than 0.4, then the pixel was classified as snow-covered). The study of Tong et al. (2020) found that for snow cover mapping in Austria, the accuracy can be (3-10% larger) if the NDSI threshold varies spatially and seasonally. The overall accuracy of snow cover mapping in Austria is larger than 97%. Table 1, which is attached as a file in Table1_NDSI_thresholds.csv, shows the final criteria used for snow cover mapping as found for Austria in Tong et al., 2020. The snow cover maps provide for each 500x500m grid information, whether it is classified as snow-covered or not, or it is not possible to classify it due to cloud cover. The limitation of the optical sensing of snow cover is that the clouds block the observation at the ground. The availability of daily observations from two satellites allows using several cloud reduction techniques if needed. More information about the cloud reduction approaches and their effectiveness in Austria can be found in Parajka et al. (2008) or Krajci et al. (2014).  The format of the grid maps is GeoTiff. The images are projected from WGS84 using the Lambert Conformal Conic projection (LCC_WGS_1984). Each image covers an area within the boundaries of (10 000, 275 000) meters and (770 000, 715 000) meters (bottom-left, top-right). The possible grid values and their corresponding classes are summarized below in Table2_Grid_value_classification.csv. File Naming Convention includes name of the satellite product (Terra or Aqua), date in the format year (YYYY) and acquisition day of year (DDD). For example: 

Terra_2017003_snowcovermap_Austria.tif refers to a grid map from Terra satellite from 3rd January 2017. Aqua_2007365_snowcovermap_Austria.tif refers to a grid map from Aqua satellite from 31th December 2007.