## Polar Products
It is important to note, however, that SRTM does not have polar coverage, being limited to areas between 60\({}^{\circ}\)S and 60\({}^{\circ}\)N (see [[http://www2.jpl.nasa.gov/srtm/datacoverage.html](http://www2.jpl.nasa.gov/srtm/datacoverage.html)]([http://www2.jpl.nasa.gov/srtm/datacoverage.html](http://www2.jpl.nasa.gov/srtm/datacoverage.html))). A global DEM based on TerraSAR-X/TanDEM-X data is scheduled for release very soon (12-m spatial resolution, 2-m relative vertical accuracy, 10-m absolute vertical accuracy), although this product is likely to be only commercially available ([[http://www.astrium-geo.com/worlddem/](http://www.astrium-geo.com/worlddem/)]([http://www.astrium-geo.com/worlddem/](http://www.astrium-geo.com/worlddem/))). Airborne laser altimetry (e.g., [111, 112, 113, 114]), satellite laser altimetry from ICESat (e.g., [115, 116]), satellite radar altimetry (e.g., [116, 117]), and data fusions, such as photoclinometry [118], have all been employed to produce DEMs. There are a few notable Antarctic DEMs produced, including an improved Antarctic Peninsula 100-m DEM ([[http://nsidc.org/data/nsidc-0516](http://nsidc.org/data/nsidc-0516)]([http://nsidc.org/data/nsidc-0516](http://nsidc.org/data/nsidc-0516))) [119, 120], the RAMP DEM (Radarsat Antarctic Mapping Project, [[http://nsidc.org/data/nsidc-0082](http://nsidc.org/data/nsidc-0082)]([http://nsidc.org/data/nsidc-0082](http://nsidc.org/data/nsidc-0082))) [121], ICESat ice sheet DEMs ([[http://nsidc.org/data/docs/daac/nsidc0304_0305_glas_dems.gd.html](http://nsidc.org/data/docs/daac/nsidc0304_0305_glas_dems.gd.html)]([http://nsidc.org/data/docs/daac/nsidc0304_0305_glas_dems.gd.html](http://nsidc.org/data/docs/daac/nsidc0304_0305_glas_dems.gd.html))) for Antarctica ([[http://nsidc.org/data/nsidc-0304.html](http://nsidc.org/data/nsidc-0304.html)]([http://nsidc.org/data/nsidc-0304.html](http://nsidc.org/data/nsidc-0304.html))) [122] and Greenland ([[http://nsidc.org/data/nsidc-0305.html](http://nsidc.org/data/nsidc-0305.html)]([http://nsidc.org/data/nsidc-0305.html](http://nsidc.org/data/nsidc-0305.html))) [123] and a DEM produced at the University of Bristol using ERS-1 radar altimetry and ICESat laser altimetry ([[http://nsidc.org/data/nsidc-0422](http://nsidc.org/data/nsidc-0422)]([http://nsidc.org/data/nsidc-0422](http://nsidc.org/data/nsidc-0422))) [124, 125, 126]. For some areas, elevation and other data are available from multiple sensors on NASA's Operation IceBridge via NSIDC ([[http://nsidc.org/data/icebridge/index.html](http://nsidc.org/data/icebridge/index.html)]([http://nsidc.org/data/icebridge/index.html](http://nsidc.org/data/icebridge/index.html))) [127, 128, 129]. In addition, ESA's Cryosat-2 is now producing elevation data at multiple levels for both ice sheet and sea ice studies ([[http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explo_rers/CryoSat-2](http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explo_rers/CryoSat-2)]([http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explo_rers/CryoSat-2](http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explo_rers/CryoSat-2))). As an aside, ice-penetrating radar has also been used to produce BEDMAP [130] and Bedmap2 [131], a digital model of the ground beneath Antarctica's ice, as well as a similar map for Greenland [132].