Cast shadows reveal changes in glacier surface elevation
-
Published:2023-08-24
Issue:8
Volume:17
Page:3535-3551
-
ISSN:1994-0424
-
Container-title:The Cryosphere
-
language:en
-
Short-container-title:The Cryosphere
Author:
Pfau Monika, Veh GeorgORCID, Schwanghart WolfgangORCID
Abstract
Abstract. Increased rates of glacier retreat and thinning need
accurate local estimates of glacier elevation change to predict future
changes in glacier runoff and their contribution to sea level rise. Glacier
elevation change is typically derived from digital elevation models (DEMs)
tied to surface change analysis from satellite imagery. Yet, the rugged
topography in mountain regions can cast shadows onto glacier surfaces,
making it difficult to detect local glacier elevation changes in remote
areas. A rather untapped resource comprises precise, time-stamped metadata on
the solar position and angle in satellite images. These data are useful for
simulating shadows from a given DEM. Accordingly, any differences in shadow
length between simulated and mapped shadows in satellite images could
indicate a change in glacier elevation relative to the acquisition date of
the DEM. We tested this hypothesis at five selected glaciers with long-term
monitoring programmes. For each glacier, we projected cast shadows onto the
glacier surface from freely available DEMs and compared simulated shadows to
cast shadows mapped from ∼40 years of Landsat images. We
validated the relative differences with geodetic measurements of glacier
elevation change where these shadows occurred. We find that shadow-derived
glacier elevation changes are consistent with independent photogrammetric
and geodetic surveys in shaded areas. Accordingly, a shadow cast on Baltoro
Glacier (the Karakoram, Pakistan) suggests no changes in elevation between 1987
and 2020, while shadows on Great Aletsch Glacier (Switzerland) point to
negative thinning rates of about 1 m yr−1 in our sample. Our estimates
of glacier elevation change are tied to occurrence of mountain shadows and
may help complement field campaigns in regions that are difficult to access.
This information can be vital to quantify possibly varying
elevation-dependent changes in the accumulation or ablation zone of a given
glacier. Shadow-based retrieval of glacier elevation changes hinges on the
precision of the DEM as the geometry of ridges and peaks constrains the
shadow that we cast on the glacier surface. Future generations of DEMs with
higher resolution and accuracy will improve our method, enriching the
toolbox for tracking historical glacier mass balances from satellite and
aerial images.
Funder
Deutscher Akademischer Austauschdienst
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Water Science and Technology
Reference73 articles.
1. Azam, M. F., Kargel, J. S., Shea, J. M., Nepal, S., Haritashya, U. K.,
Srivastava, S., Maussion, F., Qazi, N., Chevallier, P., Dimri, A. P.,
Kulkarni, A. V., Cogley, J. G., and Bahuguna, I.: Glaciohydrology of the
Himalaya-Karakoram, Science, 373, 6557, https://doi.org/10.1126/science.abf3668, 2021. 2. Bauder, A., Funk, M., and Huss, M.: Ice-volume changes of selected glaciers
in the Swiss Alps since the end of the 19th century, Ann. Glaciol., 46,
145–149, https://doi.org/10.3189/172756407782871701, 2007. 3. Beedle, M. J., Menounos, B., and Wheate, R.: An evaluation of mass-balance
methods applied to Castle creek Glacier, British Columbia, Canada, J.
Glaciol., 60, 262–276, https://doi.org/10.3189/2014JoG13J091, 2014. 4. Belart, J. M. C., Magnússon, E., Berthier, E., Gunnlaugsson, Á.
Þ., Pálsson, F., Aðalgeirsdóttir, G., Jóhannesson, T.,
Thorsteinsson, T., and Björnsson, H.: Mass Balance of 14 Icelandic
Glaciers, 1945–2017: Spatial Variations and Links With Climate, Front.
Earth Sci., 8, 163, https://doi.org/10.3389/feart.2020.00163, 2020. 5. Berthier, E., Arnaud, Y., Vincent, C., and Rémy, F.: Biases of SRTM in
high-mountain areas: Implications for the monitoring of glacier volume
changes, Geophys. Res. Lett., 33, L08502, https://doi.org/10.1029/2006GL025862, 2006.
|
|