SAR FIRN LINE DETECTION AND CORRELATION TO GLACIAL MASS BALANCE;SVARTISEN GLACIER, NORTHERN NORWAY

摘要

The glacial firn line of the Svartisen Glacier has been detected using ERS II SAR data from 1995 and up till today.The firn line is detected by first correcting the imagebackscatter intensity for topographic and geometriccontributions using the Muhleman backscattering model.Then we discriminate between firn and ice facies basedon the backscatter intensity since frozen firn has a muchhigher backscatter than ice. Transects across different areasof the glacier were chosen based on requirements ofsmoothness of topography, precipitation zones, as wellas the availability of field data for validation and comparison.From having quite stable conditions during thenineties we have observed a substantial retreat of the firnline over the last few years. The equilibrium line derivedfrom field measurements show a similar trend as the firnline changes, but it has larger year to year variability. This indicates that the firn line altitude changes may be a better indicator of climate change than the equilibrium linedue to the smaller variance.