ABSTRACT: AMSR-E algorithm for snowmelt onset detection in sub-arctic heterogeneous terrain.

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Abstract

The onset of snowmelt in the upper Yukon River basin, Canada, can be derived from brightness temperatures (Tb) obtained by the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) on NASA's Aqua satellite. This sensor, with a resolution of 14 × 8 km2 for the 36ˇ5 GHz frequency, and two to four observations per day, improves upon the twice-daily coverage and 37 × 28 km2 spatial resolution of the Special Sensor Microwave Imager (SSM/I). The onset of melt within a snowpack causes an increase in the average daily 36ˇ5 GHz vertically polarized Tb as well as a shift to high diurnal amplitude variations (DAV) as the snow melts during the day and re-freezes at night. The higher temporal and spatial resolution makes AMSR-E more sensitive to sub-daily Tb oscillations, resulting in DAV that often show a greater daily range compared to SSM/I. Therefore, thresholds of Tb > 246 K and DAV > ą 10 K developed for use with SSM/I have been adjusted for detecting the onset of snowmelt with AMSR-E using ground-based surface temperature and snowpack wetness relationships. Using newly developed thresholds of Tb > 252 K and DAV > ą 18 K, AMSR-E derived snowmelt onset correlates well with SSM/I observations in the small subarctic Wheaton River basin through the 2004 and 2005 winter/spring transition. In addition, the onset of snowmelt derived from AMSR-E data gridded at a higher resolution than the SSM/I data indicates that finer-scale differences in elevation and land cover affect the onset of snowmelt and are detectable with the AMSR-E sensor. On the basis of these observations, the enhanced resolution of AMSR-E is more effective than SSM/I at delineating spatial and temporal snowmelt dynamics in the heterogeneous terrain of the upper Yukon River basin

Bibliography of Canadian Geomorphology