Temporal changes of the volume and mass of ice sheets and glaciers are sensitive indicators of climate change, and strongly affect the global water cycle, surface energy budget, sea level change, ocean circulation patterns, and hence global climate. A precise monitoring of the behaviors of these ice bodies is essential for improved understanding of the Earth’s system, and interactions between its sub-components. Apart from this scientific motivation, these investigations are also highly relevant to society, since phenomena such as the global sea level rise are largely driven by accelerated melting of the Greenland and Antarctica ice sheets and glaciers, and could be catastrophic for millions of people in the future.
With observations from dedicated satellite gravity missions (CHAMP, GRACE, GRACE Follow-On, and GOCE), as well as remote sensing techniques from satellites and aircrafts, a precise monitoring of the mass and volume changes of the ice sheets and larger glaciers is now possible. The three following methods are currently applied to measure the mass balance and volume changes of these ice bodies:
- comparing net snow accumulation (assessed by atmospheric modeling) with ice discharge to the ocean by glacier flow, assessed through measurements of glacier flow velocities by interferometric SAR (InSAR);
- using altimetry over the ice surface to measure changes of the thickness of ice sheets and glaciers from radar (e.g., Cryosat) and laser (e.g., ICESat) altimeters (geometric method);
- measuring temporal gravity changes based on data from satellite gravity missions, directly providing estimates of mass change and mass transport (gravimetric method);