Remote sensing of glaciers

Many elements of the cryosphere respond to changes in climate, but mountain glaciers are particularly good indicators of climate change, because they respond more quickly than most other ice bodies on Earth. Changes in glaciers are easily noticed by specialists and non-specialists alike, in ways that other climate indicators, such as ocean temperature or statistics of atmospheric circulation indices, are not. Remote sensing methods are capable of measuring many parameters of mountain glaciers and the changes they exhibit, leading to greater insight into processes affecting changes in glaciers and, hence, climate. Field-based measurements are indispensable, as they yield high-precision data and give key insights into processes. However, due to expense and difficult logistics, such measurements are limited to a small number of sites. Remote sensing can cover large numbers of glaciers per image, and some long-term data collections (e.g., Landsat) are available for free. Algorithms and computational resources are now capable of producingmaps of glacier boundaries at useful accuracy over large regions in a short time.New sensors will be coming online soon that will continue and extend this capability. Mass balance is an important parameter indicating the health of a glacier. Mass balance can be estimated fromsatellite data by the “geodeticmethod” of measuring volume changes, where the change in volume is estimated by subtracting two digital terrain models of the glacier surface. A more recent approach to detect mass changes in land ice is through measurement of the gravitational field using the Gravity Recovery and Climate Experiment (GRACE) satellite system, which measures changes in mass below the orbit track. Advances have been made recently in remote sensing of glaciers on a number of fronts, including more complete and more accurate glacier inventories, improved glacier mapping techniques, and new insights fromgravimetric satellites.Through international cooperative