Measuring thickness change of glaciers from satellite data: a case
Mean thickness change of Alaskan glaciers as a function of altitude (from. Arendt et al., 2002). 1. Scientifical background. 2. Methodology. 3. Results. 4. Outlooks ...
to estimate the contribution of glaciers to sea level rise. to improve our knowledge of the regional impact of climate change on glaciers and water ressources But: Only 250 glaciers on earth with mass balance measurements (2% of the total glacierazied area, Braithwaite, 2002)
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Field measurements “glaciological method” Time consuming and expensive, harsh environment
Aerial photography “geodetic method” (Funk et al., 1997) Precise but only cover limited area (30 km2)
Airborne laser altimetry (Arendt et al., 2002) Precise, rapid, but expensive and sampling along a few profiles
Aim of this study: to demonstrate that we can use satellite images to derive glacier mass balance. A first step: the measurement of thickness change
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Data : - SPOT images - 30 precise GCPs (D-GPS) - DEM computed using PCI geomatica - same GCPs for all images
Validation data : - DEM derived from aerial photographs (same process) - Transverse profile measured each year with GPS on glaciers ),
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Stereoscopic effect
DEM #1
DEM #2 DEM #2 - DEM #1 differential DEM
Thickness change of glaciers
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! Using the fact that, out of the glaciers, no changes are expected ! 6
Planimetric adjustment based on the cross correlation of orthorectified images
Altimetric adjustment based on a polynomial fit to the bias with altitud between the 2 DEM
4 Bias between the two DEM
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Cumulated ablation calculated from a degree day model at 3 different altitudes from the 1st August to the 15th September 2000
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Out glacier : N = 4734
-= 1.5 m σ = 15.9 m
Out glacier : N = 1549446
-= -0.3 m σ = 6.2 m
On glacier : N = 3190
-= 6.2 m σ=6m
On glacier : N = 806630
-= 1.4 m σ = 2.5 m
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1994 - 2000
2000 - 2003
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1600
1700
1800
1900
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2100
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thickness change (m)
thickness change (m)
0 1500 -5
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-15 -20 -25 -30 -35
GPS profile Satellite DEM
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1800
1900
2000
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GPS profile Satellite DEM Aerial Photo. DEM
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altitude (m.a.s.l.)
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thickness change (m/a)
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1800
Altitude (m)
2100
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thinning at low altitudes Acceleration of the thinning
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" This method is suitable to measure thickness change occuring within a few years (signal over ~5 meters) Acceleration of the melting below 2400m Extend the study to the whole Mont Blanc range (effect of orientation, slope) Production of a new DEM from SPOT5 images during summer 2004 to estimate the annual mass balance With the advent of satellites with submetric resolution (0.7m for PLEIADE), a new way to semi-automatically estimate the annual mass balance of worldwide glaciers.
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Project funded by: ACI-OT Glaciers ISIS program at CNES
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