Discussions

Cloud cover exhibits large variations in space and time. Only the cloud cover estimated at the time of the satellite afternoon passage was available in this study. The cloud cover variation in a day could not be presented. However, the R-squared values in summer season remain on a high level of 0.6 (i.e. correlation coefficient equals 0.8), suggesting the cloudiness variation between day and day is reflected by the daily NDVI indicator. The agreement of NDVI index and ground observed cloudiness shows that the spatial distribution of cloud cover is captured by the drop of NDVI values. However, frozen surface soil and snow cover will hurt the NDVI relationship to clouds.