Melting on glaciers: environmental controls examined with orbiting radar

Abstract

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.

The role of meteorological forcing and snow model complexity in winter glacier mass balance estimation, Columbia River basin, Canada

“…We measured winter surface mass balance at the four glaciers since 2014 (Pelto et al, 2019) using the glaciological method (Cogley et al, 2011). The measurement networks for all four glaciers including snow depth measurement locations, and snow pit/core locations are shown in Figure 2.…”

A method for separating Antarctic postglacial rebound and ice mass balance using future ICESat Geoscience Laser Altimeter System, Gravity Recovery and Climate Experiment, and GPS satellite data

“…Because the density profile in the upper layers of the snow‐ice column depends on prior accumulation rate, the assumption of a constant ice density ρ i introduces an error in the estimate of IMT from GLAS data. It is unlikely that the variable accumulation at interannual and interdecadal periods can be reconstructed accurately enough to directly calculate variable compaction, although GLAS measurements will help to constrain it for the short term, and microwave remote sensing of scattering from ice lenses and pipes [e.g., Cogley et al , 2001] will contribute additional information. Nevertheless we expect that, as a first approximation, researchers will convert GLAS estimates of ice thickness rate of change to mass rates by simply multiplying by the maximum density of compact ice, ρ i = 917 kg/m 3 , since this is the density appropriate for the century‐scale mass variability.…”

A review of Canadian remote sensing and hydrology, 1999–2003

“…A. PIETRONIRO AND R. LECONTE Remote sensing efforts in Canada in glacier monitoring over the last 5 years have focused on estimating glacier extent, snowline detection and movement, both as a hydrological modelling input and as a surrogate for mass balance (Demuth and Pietroniro, 1999;Short et al, 2000;Cogley et al, 2001). In this context of glacier monitoring and modelling, the snowline elevation is often a desired parameter for many applications (Demuth and Pietroniro, 1999).…”

“…In order to extend the mass-balance record for Arctic glaciers, Cogley et al (2001) have developed a system that makes use of Radarsat-1 'Browse' images. These images have an effective resolution of 2 km and number about 100 scenes per year (Cogley et al, 2001).…”

“…In order to extend the mass-balance record for Arctic glaciers, Cogley et al (2001) have developed a system that makes use of Radarsat-1 'Browse' images. These images have an effective resolution of 2 km and number about 100 scenes per year (Cogley et al, 2001). In the analysis, Cogley et al (2001) determine that, rather than focus on the equilibrium line location, the time series information derived from these relatively inexpensive browse images contains useful detail on the intensity of melting; they also suggest that there is persuasive evidence that radar monitoring holds promise for estimating glacier melt rates.…”