Albedo is a reflection coefficient that describes the reflecting power of a surface. It is a ratio of the reflected to incident radiation of a surface. Albedo values are dimensionless with values from zero (no reflection) to one (perfect reflection). Fresh snow, for example, will have values near 0.9 and charcoal will have values near 0.04. Albedo depends on the frequency of radiation; therefore the standard MODIS product for Albedo includes data layers for MODIS Bands 1 through 7.
Accurately measuring albedo at high latitudes is challenging. Reflectance measurements made at high solar zenith angles pose difficulties in calibration and atmospheric correction. About half of available satellite observations during the sunlit season Summary of Products in the Arctic are obtained under conditions where the solar zenith angle exceeds 70° resulting in lower-quality results.
The standard MODIS product includes data for black sky albedo (BSA) and white sky albedo (WSA). Actual albedo is a combination of the BSA and WSA albedo, and will depend on the particular atmospheric conditions when observations are made. An accuracy assessment of the MODIS standard albedo product to in-situ measurements on the Greenland ice sheet (Stroeve et al. 2005) found that at most solar zenith angles, the BSA and WSA bracket the actual albedo, and at 50° local solar noon zenith angles, BSA and WSA were identical and therefore close to actual albedo. Additionally it was found that during spring and autumn when the solar zenith angle often exceeds 50°, the quality of the MODIS albedos was often flagged as poor (e.g., a backup algorithm was used and the statistical differences between the BSA and WSA had more to do with backup versus main algorithm retrievals than with BSA versus WSA).
This MODIS product is available on a 16-day acquisition cycle, but produced every 8 days. For the CAFF System, the first production of every month has been provided. Note: The Albedo layers of this product require a scale factor that can be found in the Appendix.
For usage please see ABDS Data Policy
Suggested citation:
CAFF (2015). Albedo: Arctic Land Cover Change Index. Conservation of Arctic Flora and Fauna, Arctic Biodiversity Data Service (ABDS).
