Melting on glaciers: environmental controls examined with orbiting radar

• Main Authors: J Graham Cogley, M A Ecclestone, D T Andersen
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2001
• Subjects: Axel Heiberg Island; Canada; Heiberg; Nunavut; glacier*
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1037.4183; http://people.trentu.ca/%7Egcogley/glaciology/papers/cogleyetal.2001.hydpro.pdf

Abstract: Direct, in situ measurements of glacier mass balance are expensive. Remote sensing would be an attractive alternative if remotely observable quantities could be interpreted in terms of mass gain or loss. A system developed recently for the analysis of Radarsat browse images is used here to explore temporal and environmental controls of melting on glaciers on Axel Heiberg Island, Nunavut, Canada. The browse images have an effective spatial resolution of 2 km, are georeferenced to single-pixel accuracy, and number about 200 over the two study years, 1998 and 1999. Surface melting in the accumulation zone is readily recognized by the contrast between bright frozen firn, which exhibits a microwave signal dominated by volume scattering from ice lenses and pipes, and dark wet firn, the signal from which is muted by either absorption or near-specular reflection at the surface. In the ablation zone, radar images, apart from showing the brief spring period of snowmelt, contain little information about the intensity or even the fact of melting. However, in the accumulation zone there is a definite dependence of brightness on temperature: at temperatures above freezing, the hotter it is the darker is the appearance of the glacier. This is most naturally (and encouragingly) interpreted as a relation between brightness and melting rate. Analysis of same-day image pairs shows that, as expected, the terrain slope and the aspect influence the radar brightness strongly and must therefore be allowed for in future modelling of the hydrology of ablation on glaciers.