 |
 |
|
|
|
 |
Snow Index - NDSIIdentifying snow cover is important for weather and hydrological forecasting. To detect the presence of snow, recent satellite instruments include observations at 0.66 and 1.6mm. The atmosphere is transparent at both these wavelengths, while snow is very reflective at 0.66 mm and not reflective at 1.6mm . The Normalized Difference Snow Index:
NDIV is used to monitor the extent of snow cover. At visible wavelengths (e.g. 0.66 microns), snow cover is just as bright as clouds, and is therefore difficult to distinguish from cloud cover. However, at 1.6 microns, snow cover absorbs sunlight, and therefore appears much darker than clouds. This allows the effective discrimination between snow cover and clouds. Values of NDSI < 0.4 typically indicate the presence of snow. The following image demonstrates the ability to separate clouds from snow using observations at these wavelengths. 
Red regions are snow covered, white regions are cloudy.
|
(29)