USING A MULTI-YEAR DATA ARCHIVE OF ERS SAR IMAGERY FOR THE MONITORING OF FIRN LINE POSITIONS AND ABLATION PATTERNS ON

• Main Authors: Matthias Braun, Frank Rau
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: King George Island; Antarc*; Antarctica; Ice cap
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.522.657; http://las.physik.uni-oldenburg.de/eProceedings/vol01_1/01_1_braun1.pdf

Multi-year SAR data is used to study the seasonal dynamic of the snow melt patterns on the ice cap of King George Island, Antarctica. The snow cover of the entire ice cap becomes wet during sum-mer months, however, in the highest elevations frequent refreeze and melt cycles are observed. Bare ice areas form in the lowest elevations of the ice cap. These findings are in good agreements with energy balance studies and results of a ground penetrating radar survey. Backscatter values in in-termediate elevations show a marked rise at the end of the ablation season. This fact is attributed to an increasing surface roughness on a wet metamorphosed snow cover at the end of the ablation sea-son. The influence of thresholds on the determination of the extent of the bare ice radar zone in summer and winter imagery as well as in ascending and descending orbit is investigated. As a con-sequence, the border of the bare ice radar zone have been mapped using thresholds of –14 dB in summer and –6 dB in winter imagery. It could be shown, that thresholds of –12 dB and –8 dB, re-spectively, do not change significantly the extent of this radar glacier zone. Firn line altitudes were mapped for several consecutive years. A low inter-annual variation of this line with elevations of about 200 m a.s.l. was observed. The maximum altitude of the firn line was recorded in the mass balance year 1996/97with about 250 m a.s.l. Comparing these values to equilibrium line positions of previous measurements indicate an upward shift in the equilibrium line altitude since the 1970’s.