The intense public debate on how rapidly the Himalayan喜马拉雅山脉的 glaciers2冰川 are retreating highlights the necessity for the constant monitoring of glaciers worldwide by satellites. Since glaciers are among the most reliable indicators指示器 of climate change and because they can have a major influence on water availability水资源可利用量, knowledge of the recent changes and future behaviour is of great interest for climate scientists and governing bodies. A key to assess these changes or to model their future evolution is the existence of a detailed4 glacier1 inventory5存货，库存.
Data from satellites allow scientists to measure glacier extent in detail, providing authoritative有权威的 evidence of trends. They also allow local measurements to be expanded to a regional scale. Considering the valuable role satellites can play in determining the state of Earth's glaciers, the Global Climate Observing System全球气候观测系统 (GCOS) has called for the systematic7 monitoring of glaciers by satellites in support of the UN Framework Convention on Climate Change.
In 2007, ESA started the GlobGlacier project as a major effort to develop and apply existing methodologies方法论 to monitor glaciers and contribute to a global glacier inventory using satellite observations. GlobGlacier, part of ESA's 'Data User Element', is adding about 20 000 of the estimated 160 000 glaciers worldwide to this inventory to allow their histories to be adequately tracked.
Kashmir, part of the Indian Himalayas, is one of the selected regions where little information is available on overall glacier extent or changes. GlobGlacier is creating inventory data for more than 1000 glaciers in this region.
The inventory combines information on glacier outlines based on archived归档的，存档的 satellite data from the Landsat地球资源卫星 Thematic题目的，主题的 Mapper制图人，测绘仪 (TM) and the Enhanced Thematic Mapper Plus (ETM+) instruments with topographic地形学上的 information from the Shuttle Radar8 Topography Mission and the Global Digital Elevation9 Model (GDEM) from ASTER10 (Advanced Spaceborne Thermal11 Emission12 and Reflection Radiometer).
When a time series of suitable images are available for a certain region, changes in glacier length and extent can be calculated. "Such data allow scientists to assess the overall pattern of changes in a larger region for a better determination of climatic change impacts," said GlobGlacier Project Manager Frank Paul from the University of Zurich.
The above animation13, based on data acquired by Landsat's TM on 15 November 1990 and by ETM+ on 1 August 2001, illustrates14 the changes in glacier extents that occurred during this time in the region northeast of the Gangotri Glacier, situated位于，处于 in Garwhal Himalaya.
While most of the smaller and debris-free glaciers show considerable retreat in this period, the larger glaciers with completely covered tongues have not changed much. Several of the pro-glacial lakes have grown. Quite a few glaciers at lower altitudes are nearly free of snow in the August 2001 image, indicating a retreat that year.
ESA's ERS-1, ERS-2 and Envisat Advanced Synthetic16 Aperture17 Radar (ASAR) data are providing velocity18 measurements速度测量 of selected glaciers. The image to the right shows the surface velocity field速度场，流速场 for the Baltoro Glacier in Pakistan based on Envisat ASAR data from 2003 to 2008.
ESA's new Climate Change Initiative, which will produce robust强健的 long-term records of essential climate variables变量, will build on the results of the GlobGlacier project by further improving the algorithms算法 for glacier monitoring and continually updating the related glacier inventory information.
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