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data overview



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Within GTN-G, datasets can be thematically categorized into those related to glacier distribution and those with information on glacier changes. From an operational point of view, we discriminate between operational databases that are regularly updated by the data services with the help of the research community and index datasets representing snapshot compilations which usually result from projects out of the research community.


Glacier distribution
The need for a detailed inventory of the world’s glaciers evolved during the International Hydrological Decade (1965-1974). Today, there are two operational databases:

(a) the World Glacier Inventory (WGI; WGMS and NSIDC 1989, updated 2012) based primarily on aerial photographs and maps of the second half of the 20th century and

(b) the Glacier Land Ice Measurements from Space database (GLIMS 2011) which is the continuation of the WGI task primarily based on satellite data from the 21st century.

In the WGI, glaciers are represented by geographical point coordinates. The GLIMS database includes digital outlines. Both include exact time stamps and tabular information on glacier classifications, length, area, orientation, and altitude range. Note that any new or repeat inventory including digital outlines is supposed to be stored in the GLIMS database.


Since these detailed glacier inventories are not (yet) globally complete, there have been several efforts towards preliminary estimates of the overall global glacier coverage. A first, well elaborated one was included in the original status report of the WGI (WGMS 1989) and was later refined with information from other sources by Dyurgerov and Meier (2005). Other studies used the detailed WGI for regional up-scaling (e.g., Meier and Bahr 1996) or the extended format of the WGI by Cogley (2008; 2010) for a global up-scaling of glacier extents (Radić and Hock 2010). Cogley (2003, updated 2007) provided a global map of percentage glacier coverage (GGHydro) per 1°x1° grid box that is widely used for modelling at global scale. A first globally and almost complete map with (generalized) digital outlines of all ice covered regions (incl. Greenland but excluding Antarctica) was derived from ESRI’s Digital Chart of the World (DCW; Danko 1992) and other sources by Raup et al. (2000). Most recently, Arendt et al. (2012) combined available outlines from the GLIMS, DCW, and WGI datasets as well as from many other (often unpublished) sources by using the highest quality version in each region. However, while having the advantage of being almost complete, these global estimates lack datestamps and attributes for individual glaciers.


Glacier changes
The internationally coordinated compilation of standardized information on glacier changes over time was initiated at the end of the 19th century. Today data on glacier changes in length, area, volume, and mass are digitally stored in and disseminated from the Fluctuations of Glaciers (FoG) database and periodically published:

at five-years interval in the Fluctuations of Glaciers series (WGMS 2008, and earlier issues) and

bi-annually in the Glacier Mass Balance Bulletin series (WGMS 2011, and earlier issues).

The FoG database is designed to store change information related to individual glaciers in order to allow clearly defined spatio-temporal comparisons. Recent advances in remote sensing of glaciers has resulted in large data streams of regional glacier change assessments, such as elevation changes derived from the SRTM mission compared to regional and national DEMs (e.g., Larsen et al. 2007, Paul and Haeberli 2008), repeat airborne (Arendt et al. 2002) and space-borne (e.g., Gardner et al. 2011) laser altimeter surveys, and gravimetric mass balance estimates from the GRACE mission (e.g., Gardner et al. 2011, Jacob et al. 2012). These new datasets provide change estimates representative for whole glacierized regions or even entire mountain ranges but typically are difficult to break down to individual glaciers.


Other datasets
Within GTN-G, the following additional datasets are made available which provide important meta-information related to the distribution and changes of glaciers:

 

Continue here for references and data access!



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image: ellesmere island, aster
last change 19/MAR/2012, mze