2. Cloud mask algorithm flags are set for 'probably cloudy' and 'probably clear' sky conditions in the algorithm flags QA data set.
- Daily snow-cover record from MODIS begins on February 24, 2000, representing more than two decades of moderate-resolution (500 m) snow-cover maps (Hall et al., 2019)
- 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).
- 8-day snow-cover maps show maximum extent of snow cover over an 8-day period (Hall and Riggs, 2007).
- 8-day snow-cover maps minimize cloud cover by using clear observations in the period, however cloud cover persisting for 8 days is mapped (Riggs et al., 2019).
- 8-day snow-cover maps include persistent cloud cover, polar darkness and other features (Riggs et al., 2019).
- Snow cover may not be mapped during a given 8-day period if a snowfall occurred and resulting snow on the ground melted before the clouds cleared (Riggs et al., 2019).
- Cloud cover is biggest limitation to use of MODIS snow-cover products, which can prevent mapping of some snow (Hall and Riggs, 2007).
- Areas of ephemeral snow cover and very thin snow cover may not be mapped by MODIS (Hall et al., 2010).
- Polar darkness prevents snow-cover mapping in polar regions during the winter (Riggs et al., 2019).
- Because this product represents an 8-day period, most users would be better-served to use MOD10A1F (daily cloud-gap-filled) product instead (Hall et al., 2010; Riggs et al., 2019). Using MOD10A1F, a unique compositing period may be selected.