Abstract
Since 2000, a vast archive of stereo-images has been built by the Advanced Spaceborne Thermal Emission and Reflection (ASTER) satellite. Several studies already extracted glacier mass balances from multi-temporal ASTER digital elevation models (DEMs) but they lacked accurate independent data for validation. Here, we apply a linear regression to a time series of 3D-coregistered ASTER DEMs to estimate the rate of surface elevation changes (dh/dtASTER) and geodetic mass balances of Mont-Blanc glaciers (155 km²) between 2000 and 2014. Validation using field and spaceborne geodetic measurements reveals large errors at the individual pixel level (> 1 m a-1) and an accuracy of 0.2-0.3 m a-1 for dh/dtASTER averaged over areas larger than 1 km². For all Mont-Blanc glaciers, the ASTER region-wide mass balance (-1.05±0.37 m water equivalent (w.e.) a-1) agrees remarkably with the one measured using Spot5 and Pleiades DEMs (-1.06±0.23 m w.e. a-1) over their common 2003-2012 period. This multi-temporal ASTER DEM strategy leads to smaller errors than the simple differencing of two ASTER DEMs. By extrapolating dh/dtASTER to mid-February 2000, we infer a mean penetration depth of about 9±3 m for the C-band Shuttle Radar Topographic Mission (SRTM) radar signal, with a strong altitudinal dependency (range 0-12 m). This methodology thus reveals the regional pattern of glacier surface elevation changes and improves our knowledge of the penetration of the radar signal into snow and ice.
Highlights
In response to global warming, glaciers are losing mass nearly everywhere on Earth and significantly contribute to sea level rise (Vaughan and Comiso, 2013)
We validated the rate of surface elevation changes and region-wide geodetic mass balances derived from multitemporal ASTER digital elevation models (DEMs) over the Mont-Blanc area
A specificity of our methodology is that the exclusion of outliers in the ASTER DEMs is based on a linear fit to the elevation time series and does not require choosing an a priori threshold on the maximum accepted rates of thinning/thickening in the ablation/accumulation areas
Summary
In response to global warming, glaciers are losing mass nearly everywhere on Earth and significantly contribute to sea level rise (Vaughan and Comiso, 2013). The global glacier mass loss is relatively well-constrained during 2003–2009 thanks to the combined availability of field measurements, spaceborne laser altimetry (ICESat), and gravimetry (GRACE) data (e.g., Gardner et al, 2013). Outside of this short 6-year time window, our knowledge of global and region-wide glacier mass balances is more uncertain. The geodetic method, based on the differencing of digital elevation models (DEMs) derived from historical maps and satellite data, is one of the alternatives to the above-mentioned techniques of mass balance measurements, in particular for regional assessment of geodetic glacier mass balances (e.g., Gardner et al, 2012; Gardelle et al, 2013; Pieczonka and Bolch, 2015)
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