Landsat Fractional Snow Covered Area: Mapping Snow Pixel by Pixel

Dixie National Forest, Utah, on February 28, 2021: left, a Landsat 8 surface reflectance image (bands 6, 5 and 4); center, fractional snow covered area; right, the canopy-adjusted version. USGS images.

What it is

The Landsat Collection 2 Level-3 Fractional Snow Covered Area (fSCA) science product gives the percentage of each pixel covered by snow in imagery from Landsat 4–9.

Snow cover varies across space and time and is often concentrated in remote or inaccessible places, which makes satellite remote sensing the most practical way to measure and monitor it. Landsat's spatial resolution can map snow patterns across rugged mountain terrain.

• Resolution and grid: 30-meter pixels in the Albers Equal-Area Conic projection on the WGS 84 datum, gridded to a common tiling scheme.
• Formats: Cloud Optimized GeoTIFF files for the rasters, with spatial reference embedded in them, and XML metadata.

Coverage

The western, northern and northeastern conterminous United States, and Alaska:

What's new in Collection 2

• More ground: coverage now includes the northern conterminous U.S. and the Aleutian Islands.
• Canopy shown separately: the single Collection 1 band is split into fSCA and Canopy Adjusted fSCA, showing whether the results of the snow cover area and grain size (SCAG) model were adjusted for canopy cover.
• New bands: SCAG Shade Endmember and SCAG Model Mask.

What's in the package

Each acquisition-based package holds these bands, plus a metadata file:

• fSCA (new): the share of each pixel covered by snow visible from the instrument.
• Canopy Adjusted fSCA (new): the same share, adjusted for canopy.
• SCAG Shade Endmember (new): the share of each pixel covered by shade visible from the instrument.
• SCAG Model Mask (new): whether each pixel was modeled successfully — and, for Thematic Mapper and Enhanced Thematic Mapper Plus, which saturation run filled it.
• fSCA QA: a mask, based on the Level-1 quality flags, marking fill, cloud, cirrus, revised cloud, water, terrain shadow and National Land Cover Database fill.

Statistics

Also new in Collection 2 are fSCA statistics: mean snow cover fraction and clear-pixel counts for set time steps from 1984 to the current year — 5-year ranges and the whole U.S. Analysis Ready Data record. Each package covers one tile, with annual and mean annual files (and monthly ones for the whole record) of viewable or ground snow cover. They're updated every February.

Getting the data

• EarthExplorer: at earthexplorer.usgs.gov, under Landsat › Landsat Collection 2 Level-3 Science Products or Landsat C2 U.S. Analysis Ready Data (ARD), listed as "Landsat 4-9 C2 Fractional Snow Covered Area." The statistics are a separate dataset in the same place, "Landsat 4-9 C2 fSCA Statistics."
• The commercial cloud: see Landsat Data Access for cloud access and bulk downloads.
• Documentation: the product page has the product guide and the algorithm description.

Using and citing it

Use of Landsat science products is not restricted. Citing is optional, but the USGS suggests crediting "Landsat Collection 2 Level-3 Fractional Snow Covered Area science product courtesy of the U.S. Geological Survey," along with the research behind it:

• Painter and others (2009), on retrieving subpixel snow covered area, grain size and albedo from MODIS, Remote Sensing of Environment 113(4): 868–879;
• Rittger and others (2021), evaluating VIIRS and MODIS snow cover fraction in High-Mountain Asia using Landsat 8 OLI, Frontiers in Remote Sensing 2: 647154;
• Selkowitz and others (2017), "The USGS Landsat Snow Covered Area Product — Methods and preliminary validation," the work the product is directly based on, from a University of Utah Ph.D. dissertation.

Sources

Based on U.S. Geological Survey, "Landsat Collection 2 Level-3 Fractional Snow Covered Area Science Product," Fact Sheet 2022–3086, version 1.1, June 2023, USGS; a work of the United States government in the public domain. The figure is restored from the fact sheet's PDF.