2. Cloud mask algorithm flags are set for 'probably cloudy' and 'probably clear' sky conditions in the algorithm flags QA data set.
- The daily snow-cover maps provide an excellent representation of the extent of snow cover at 500-m resolution in areas that are cloud-free (Hall and Riggs, 2007).
- The daily snow-cover record from MODIS begins on February 24, 2000, and thus represents more than two decades of moderate-resolution (500 m) snow-cover maps (Hall et al., 2019)
- The daily MODIS snow-cover record is useful to assess regional snow cover and trends (Riggs and Hall, 2020).
- The MODIS snow-cover products provide Normalized Difference Snow Index (NDSI) values from 0 – 100. Users can use the NDSI as is or convert it to fractional or binary snow cover (Salomonson and Appel, 2004; Riggs et al., 2019). There are flag values for other features in a scene (e.g., clouds).
- The daily snow-cover maps include cloud cover, polar darkness and other features (Riggs et al., 2019).
- The biggest limitation to the use of the MODIS snow-cover products is cloud cover, which can prevent mapping of some snow (Hall and Riggs, 2007).
- Polar darkness prevents snow-cover mapping in polar regions during the winter (Riggs et al., 2019).
- Areas of ephemeral snow cover and very thin snow cover may not be mapped by MODIS (Hall et al., 2010).