Quantifying geodetic mass balance for South American glaciers since the 1970s using KH-9 Hexagon imagery and ASTER DEMs
Abstract
South American glaciers provide a unique opportunity to study glacier-climate interactions across a wide range of climates and geomorphological settings. The retreat of these glaciers also contributes to global sea level rise and threatens regional hydropower generation and water resources. Despite their scientific and societal importance, South American glaciers are some of the least studied in the world. In this study we quantify the spatial variation in geodetic mass balance since the 1970s for large (>3 km2) glaciers in South America utilizing digital elevation models (DEMs) and geomorphic change detection. To quantify geodetic mass balance for the period 1975-2020, we utilize declassified KH-9 Hexagon imagery and multitemporal ASTER DEMs. The steps include: (1) generating DEMs from the historical imagery and coregistering all DEMs to a NASADEM reference DEM, (2) calculating elevation change over glacier surfaces, and (3) converting elevation changes to mass balance. We process the 1970s stereo-imagery using HEXIMAP (Hexagon Imagery Automated Pipeline) to generate historical DEMs. ASTER DEMs acquired within the 2000-2020 period are processed to remove saturated pixels and errors resulting from clouds. Both Hexagon and ASTER DEMs are coregistered to the same reference DEM. The Hexagon DEMs are differenced with ASTER DEMs from the year 2000 to calculate elevation change over glacier surfaces for the historical period 1975-2000. For the 2000-2020 period, ASTER DEMs are input into the Random Sample Consensus (RANSAC) trend fitting algorithm to find average elevation change on glacier surfaces over the twenty-year period. For both periods (1975-2000, 2000-2020), elevation changes are integrated over the glacier surfaces, normalized to glacier area, and then converted to geodetic mass balance using snow/ice density estimates. These new glacier mass balance estimates provide key insights into how glaciers have been responding to changes in climate over the last 40+ years in South America, a region that has generally lacked spatially extensive, multi-decadal estimates. These results also provide invaluable insights for improving estimates of mountain glacier contribution to sea level rise, and will hopefully assist in future continent-wide policy-making, energy choices and water resource planning.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMGC0260006M
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 0799 General or miscellaneous;
- CRYOSPHERE;
- 1616 Climate variability;
- GLOBAL CHANGE;
- 1630 Impacts of global change;
- GLOBAL CHANGE