Monitoring snowmelt across the Arctic forest-tundra ecotone using Synthetic Aperture Radar

Detailed snowpack observations, meteorology, topography and landcover classification were integrated with multi-temporal SAR data to assess its capability for landscape scale snowmelt mapping at the forest-tundra ecotone. At three sites along an approximately 8 degrees latitudinal gradient in the Fennoscandian mountain range, 16 multi-temporal spaceborne ERS-2 synthetic aperture radar (SAR) were used for mapping snowmelt.

Comparison of field measurements and backscatter values demonstrates the difficulty of interpreting observed backscatter response because of complex changes in snow properties on diurnal and seasonal temporal scales. Diurnal and seasonal melt-freeze effects in the snowpack, relative to the timing of ERS-2 SAR image acquisition, effectively reduce the temporal resolution of such data for snow mapping, even at high latitudes.

The integration of diverse data sources did reveal significant associations between vegetation, topography and snowmelt. Several problems with the application of thresholding for the automatic identification of snowmelt were encountered. These largely related to changes in backscattering from vegetation in the late stages of snowmelt. Due to the impact of environmental heterogeneity in vegetation at the forest-tundra ecotone, we suggest that the potential to map snow cover using single polarization C-band SAR at the forest-tundra ecotone may be limited to tundra areas.