Near Real-Time MODIS/Terra L3 Global Daily 500m SIN Grid Snow Cover, Snow Albedo, and Snow Surface Properties, Version 2

This data set contains the following parameters: snow fraction (on the ground), viewable snow fraction, snow cover duration, snow grain size, dust concentration, snow albedo (on horizontal surface), snow albedo (on sloped surface), and radiative forcing. A quality layer tracks the days since the last clear sky observation. All variables are spatially and temporally complete after interpolation.<br/><br/>

The data set is derived from a version (<a href="https://github.com/RittgerLabGroup/SPIRES_2025_0_1">Rittger et al, 2025</a>) of the spectral mixture analysis (SMA) approach called the Snow Property Inversion from Remote Sensing (SPIReS, <a href="https://www.sciencedirect.com/science/article/pii/S0034425725001464?via%3Dihub#bb0040">Bair et al, 2021</a>). This dataset uses surface reflectance inputs from <a href="https://lpdaac.usgs.gov/products/mod09gav061/">MOD09GA v6.1</a> and includes additional outputs not included in the original version of SPIReS: snow albedo, snow radiative forcing, snow cover duration, and days since last observation.<br/><br/>

The SPIReS SMA model considers three spectral endmembers: snow, shade, and a snow-free background reflectance, which is identified for each MODIS pixel as the minimum MOD09GA reflectance measured typically between 1 August and 30 September for a given year in the Northern Hemisphere. Dust concentration is solved for simultaneously with fractional snow covered area (fSCA) and snow grain size during the spectral unmixing process. Snow albedo are derived using a lookup table that incorporates snow grain size, dust concentration, and surface illumination (<a href="https://www.sciencedirect.com/science/article/pii/S0034425725001464?via%3Dihub#bb0025">Bair et al., 2019</a>). After the fSCA, grain size, and dust concentration are determined, these properties are filled, smoothed, and adjusted for canopy gap size and satellite viewing angles, shade, and permanent ice. SPIReS radiative forcing is derived using a lookup table that incorporates dust concentration and clear sky incoming solar irradiance. Data are available from 01 October 2025 to present. These data are provided in the netCDF-4 format with a Sinusoidal projection and and are currently available for the Western and Midwest United States (MODIS tiles: h08v04, h08v05, h09v04, h09v05, h10v04, h10v05, and h11v04) and New Zealand (MODIS tile: h29v13 and h30v13). Additional tiles in western North America and other regions will be added over time. Note that these data are used in the <a href="https://nsidc.org/snow-today/snow-viewer">Snow Today Daily Snow Viewer</a>. For data prior to 01 October 2025, please see the historical dataset (<a href="https://doi.org/10.7265/a3vr-c014">Rittger et al., 2025</a>).<br/><br/>

Data can be accessed via ftp://dtn.rc.colorado.edu/shares/snow-today/gridded_data/SPIRES_NRT_V02