EXTRACTION OF BLUE ICE AREA USING ALBEDO VALUE DERIVED FROM LANDSAT-8 SATELLITE DATA
Blue Ice Areas (BIAs) or bare ice areas are zones of glacier where surface mass balance is negative, sublimation forms the major ablation process and surface albedo is relatively small. Exceptionally dry and windy meteorological conditions over Antarctica favor the formation of large areas of net ablation on the ice sheet leading to formation of BIRs (Schytt, 1961). BIAs are major source of drinking water to research stations and serve as runways for airplanes in Antarctica. This study has been conducted on the Polar Record Glacier (PRG), Princess Elizabeth Land, East Antarctica, where more than 30% of area is covered by BIAs. The BIAs are extracted and estimated using the value of albedo which is the fraction of solar energy reflected from the surface back to space. A surface having a higher (lower) reflectivity occupies higher (lower) albedo. With an average value of blue ice albedo (also known as bare ice) of 0.55, it ranges from 0.52 to 0.66, due to its geographical area, katabatic wind and wind patterns, the direction of ice flow, rate of sublimation and ablation, surface temperature, etc. The extent of BIAs also depends upon climate and seasonal changes. Albedo is calculated using the Level-1 product of Landsat, this data product (images) is processed according to standard parameters such as Geo-referencing, re-sampling, re-projection and north-up image re-orientation. These data (Digital Numbers) were further calibrated to standard pixel value using multiplicative and additive rescaling factors from metadata provided with the Level-1 product and scaled for absolute reflectance. A further algorithm was applied to get albedo from Landsat-8 dataset. After processing the data, we detected some error in a few pixels, (∼20) which was normalized by using band math. Our result indicates that the range of albedo for the BIAs is decreasing (more surface absorption of solar radiation), which subsequently could promote warming of surface due to increase in the surface temperature. The decreasing rate of albedo suggest the possibility of less reflection of radiation to the atmosphere, more melting which leads to depletion in the BIAs. The carry home message is that the variation in different parameters like albedo of the glacier causes significant variation in the surface area and spatial extent of BIAs.