Observing glaciers in motion from space Europe's mountains are home to many glaciers. Satellite-based sensors are helping scientists keep a closer eye on these glaciers, improving anticipation of destructive avalanches and flooding. Climate Change and Environment © PhotoDisc Glaciers form when snow accumulated during the winter exceeds snow lost to melting during the summer. As the snow compacts and eventually turns to ice, the glacier deforms and moves like a fluid, albeit on very long timescales. Understanding glacier dynamics is key to preventing damage from glacier hazards. The dangers are many and include snow, ice and rock avalanches as well as flooding during glacial melts. The effects of such events range from loss of human life to structural damage and agricultural losses. Many mountain ranges in Europe, most notably the Alps, provide the right growing conditions for glaciers to form. In order to protect Europe's human and other resources against the glacial threat, Cemagref turned to satellites. Cemagref, a public research institute in France, acquired Synthetic Aperture Radar (SAR) images from the European Remote-Sensing (ERS) satellites, ERS-1 and ERS-2. Evaluation of SAR images can provide vital information about the extent and movement of glaciers. Other methods to gather such data exist, namely ground-based measurements using special markers. However, many glaciers are very remote and ground-based measurements are not feasible. In places where it is possible, the coverage is often limited and expensive to perform on a regular, year-round basis. SAR Interferometry works by comparing images taken from slightly different viewing angles. Changes in the glacier's position can be detected with a high degree of spatial and temporal resolution. Cemagref assessed the quality of SAR-derived velocity data by comparing it with ground-based measurements for two French glaciers, Mer de Glace and Argentiere. The results indicated that following requisite processing, the SAR-based measurements provided an ideal alternative. Data collection and validation over longer timeframes is necessary to fully investigate the capabilities of this new method. The information obtained has value for improving understanding of glacier dynamics and forecasting potential dangers. Europe must be on guard, especially as global warming appears to be increasing the threat of glacier hazards.