SRTM v4.1 (CGIAR-CSI)

SRTM v4.1 is based on the finished-grade 2006 SRTM v2 release by NASA that was post-processed and published in 2008 by CGIAR-CSI (Consortium for Spatial Information). The SRTM v4.1 data set offers 3 arc-second (approximately 90 meters) spatial resolution and covers about 80% of Earth’s landmass, between 60° North and 56° South. SRTM v4.1 is divided onto 5° x 5° of latitude and longitude tiles in “geographic” projection, shown here . The original SRTM v2 release contained voids (areas not or not well observed by the SRTM radar), mostly occurring in topographically steep terrain. The overcome this problem, CGIAR-CSI focused on filling the voids (holes) using various interpolation techniques, such as Kriging, moving window averaging, and importantly, the use of auxiliary elevation data sets (DEMs from other sources, e.g., national DEMs). CGIAR-CSI DEM v4.1 data comes at 5 deg x 5 deg tiles, and has a typical file size of 23 MB for one tile, which comprises two kinds of information; the DEM file and a mask file. The mask file is a binary file which identifies areas within the DEM that have been interpolated. The SRTM v4.1 datasets are available in ArcInfo ASCII and GeoTIFF (.tif) formats. Geodetic information: The SRTM V4.1 DEMs are vertically referenced to the EGM96 geoid and horizontally referenced to the WGS84 (World Geodetic System 1984). Further notes: This data set contains artefacts, e.g., pits or steps, over parts of the Himalayas, the Andes and other mountainous regions. Artefacts in SRTM v4.1 tend to occur over void-filled areas. The SRTM DEM represents bare ground elevations only where vegetation cover and buildings are absent. Over most areas, the DEM elevations reside between the bare ground (terrain) and top of canopies (surface), so are technically a mixture of a terrain and surface model. Data access to the v4.1 data set: A detailed description is found at http://www.cgiar-csi.org/data/srtm-90m-digital-elevation-database-v4-1 and access is possible via the data search page on http://srtm.csi.cgiar.org/SELECTION/inputCoord.asp . References: Reuter H.I, A. Nelson, A. Jarvis, 2007, An evaluation of void filling interpolation methods for SRTM data, International Journal of Geographic Information Science, 21:9, 983-1008. Available on http://srtm.csi.cgiar.org/download/Reuteretal2007.pdf