Response of the normalized difference vegetation index to varying cloud conditions in Arctic tundra environments

Frequent cloud cover is a major environmental constraint to optical remote sensing studies in Arctic locations, including studies based on ground or a ircraft observations. The objective of this study was to determine how clou d induced variations in solar illumination affect the normalized difference vegetation index (NDVI) of representative vegetation types on the North Sl ope of Alaska. Illumination conditions were quantified using a cloud index (incident shortwave radiation at the surface divided by radiation at the to p of the atmosphere). The results indicated that the NDVI was stable across a wide range of cloud index values, particularly when the value exceeded 0 .5. It is concluded that a cloud index threshold may be used to select unbi ased NDVI values from a data set collected under varying illumination condi tions.