Data access

theia.cnes.fr

Presentation

The Theia snow product indicates the snow presence or absence on the land surface every fifth day if there is no cloud. This 20 m resolution product is derived from Sentinel-2 L2A images generated by Theia and for this reason, covers only the areas which are produced at level 2A by Theia.

This is a first release and we are aware of three main issues that should be addressed in the next releases:

  1. Some cold, low elevation, clouds can be wrongly classified as “snow”. These clouds have a spectral signature similar to the one of the snow cover.
  2. Shaded, steep, snow covered slopes can be wrongly classified as “no-snow”, especially in winter when the sun elevation angle is low at the time of the image acquisition. These slopes have a low signal-to-noise ratio and should be considered as no-data.
  3. The product is not reliable in areas of dense forest because the canopy obstructs the surface.

Contact

Simon Gascoin
Cesbio
@S.Gascoin

Manuel Grizonnet
Cnes
@M.Grizonnet

Level

The product is distributed by Theia as a raster file (8 bits GeoTIFF) of 20 m resolution and a vector file (Shapefile polygons)

  1. Raster files are named SENTINEL2A*SNW_R2.tif. Pixels are coded as follows:
    • 0: No-snow
    • 100: Snow
    • 205: Cloud including cloud shadow
    • 254: No data
  2. Vector files are named SENTINEL2A*SNW_R2.{shp,shx,prj,dbf} and coded with the DN field
    • 0: No-snow
    • 100: Snow
    • 205: Cloud including cloud shadow
    • 254: No data

Style files to display the snow product in QGIS (raster and vector) are provided here : http://tully.ups-tlse.fr/grizonnet/let-it-snow/tree/develop/styles.

This video tutorial shows how to download a product from your web browser and display it in QGIS. You can also use this script in python to download the products from your terminal.

Format

The processor code and its documentation are available under a free software licence, here: http://tully.ups-tlse.fr/grizonnet/let-it-snow