Abstract
Surface albedo partitions the amount of energy received by glacier surfaces from shortwave fluxes and modulates the energy available for melt processes. The ice-albedo feedback, influenced by the contamination of bare-ice surfaces with light-absorbing impurities, plays a major role in the melting of mountain glaciers in a warming climate. However, little is known about the spatial and temporal distribution and variability of bare-ice glacier surface albedo under changing conditions. In this study, we focus on two mountain glaciers located in the western Swiss Alps and perform a cross-comparison of different albedo products. We take advantage of high spectral and spatial resolution (284 bands, 2 m) imaging spectrometer data from the Airborne Prism Experiment (APEX) and investigate the applicability and potential of Sentinel-2 and Landsat 8 data to derive broadband albedo products. The performance of shortwave broadband albedo retrievals is tested and we assess the reliability of published narrow-to-broadband conversion algorithms. The resulting albedo products from the three sensors and different algorithms are further cross-compared. Moreover, the impact of the anisotropy correction is analysed depending on different surface types. While degradation of the spectral resolution impacted glacier-wide mean albedo by about 5%, reducing the spatial resolution resulted in changes of less than 1%. However, in any case, coarser spatial resolution was no longer able to represent small-scale variability of albedo on glacier surfaces. We discuss the implications when using Sentinel-2 and Landsat 8 to map dynamic glaciological processes and to monitor glacier surface albedo on larger spatial and more frequent temporal scales.
Highlights
Glacier surface albedo crucially determines the amount of energy absorbed by snow/ice surfaces throughout the year
We convolved the Airborne Prism Experiment (APEX) dataset to different spectral and spatial resolutions considering the characteristics of S2 and Landsat 8 (L8) to investigate the impact of spectral and spatial resolution of satellite imagery on mean glacier-wide shortwave broadband albedo
A more systematic analysis indicates that a decreasing spectral resolution and sampling from 284 bands to 12 bands, and to 7 bands, respectively, corresponds to an increase in glacier-wide mean albedo by about 6% for FG and about 4% for Plaine Morte (PM), regardless of the spatial resolution
Summary
Glacier surface albedo crucially determines the amount of energy absorbed by snow/ice surfaces throughout the year. In summer, when large parts of the glaciers are snow-free, the albedo of heterogeneous bare-ice surfaces has a substantial impact on glacier melt rates and is highly relevant regarding the climate change response of mountain glaciers and ice caps [1,2,3,4]. An operational broadband albedo product tailored for mountain glaciers is, still lacking. Current glacier mass balance models rely mostly on simplified homogeneous ice albedo parameters in their energy balance functions, neglecting the diversity of glacier surfaces and their changes over time [9]. A widespread darkening of glacier surfaces during recent decades justifies the increasing importance and need of actual glacier albedo data. Ice albedo has received relatively little interest far
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