In 1994, an international group of scientists came together to form GLIMS (Global Land Ice Measurements from Space), a worldwide initiative to monitor and study glaciers using satellite data. For at least one hundred years, scientists had primarily used traditional field measurements to track glacier dynamics, but field data are by necessity limited in scope, and can be expensive and laborious to obtain.
The GLIMS team ultimately chose to use an imaging system called Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), jointly managed by NASA and Japan, for their glacier measurements. ASTER is installed aboard Terra, the flagship satellite of NASA’s Earth Observing System (EOS), which was launched in December 1999. ASTER data can be used to map land surface temperature, reflectance, and elevation, which allows the scientists to distinguish between glacier ice and snow and to measure changes in glacier volume.
Using digital images and data provided by ASTER, GLIMS created an up-to-the-minute database of the world’s glaciers, which includes ID, name, cross-references, and analysis of the state and dynamics of individual glaciers. In August 2014, GLIMS published their findings in book form: Global Land Ice Measurements from Space compiles these glacier profiles, provides a review of analysis methodologies for measuring changes in glacier volume, and offers predictions for future glacier change as well as some interpretations of potential impacts for policymakers in the context of climate change. The GLIMS scientists provide firm evidence that glaciers are shrinking worldwide, and they believe the cause is global warming.
The GLIMS book offers a basic theoretical background in glacier monitoring and mapping as well as remote sensing techniques. It also discusses measurements of glacier thinning from digital elevation models (DEMs), and calculation of surface flow velocities from satellite images. DEMs can provide specific data for every pixel in a satellite image, with a margin of error at 0.5m/year. Although cloud cover can interfere with accurate satellite data on glaciers, scientists are able to identify and discard this faulty data.
As described in the book, GLIMS scientists Siri Jodha Singh Khalsa and his colleagues have been able to assess the mass balance of alpine mountain glaciers by comparing historical topographic maps and DEMs derived from ASTER. For instance, they built a model and limited the error in the computation of mass balance from field measurements of China’s Sarytor glacier to less than 150mm/year.
Similarly, using techniques established by Dr. Todd Albert,who is also a member of GLIMS, a set of images of the Quelccaya Ice Cap spanning four decades was analyzed to create a history of ice surface area. Overall, Albert found that the ice cap has retreated from 58.9 km2 in 1975 to 40.8 km2 in 2010, with a loss of surface area of 31%. This history matches what has been observed in the field by glaciologists Lonnie Thompson and Henry Brecher since the 1970s.
Thanks to GLIMS, the rate of glacier melting can be measured and documented more precisely, providing readers with potential evidence of climate change. The GLIMS data provides solid support for future scientific research and planning in the face of climate change.
For other stories on the measurement of glaciers, look here.