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The Shuttle Radar Topography Mission (SRTM) is an international research effort that obtained digital elevation models on a near-global scale from 56° S to 60° N, to generate the most complete high-resolution digital topographic database of Earth prior to the release of the ASTER GDEM in 2009. SRTM consisted of a specially modified radar system that flew on board the Space Shuttle Endeavour during the 11-day STS-99 mission in February 2000, based on the older ''Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar'' (SIR-C/X-SAR), previously used on the Shuttle in 1994. To acquire topographic (elevation) data, the SRTM payload was outfitted with two radar antennas.〔 One antenna was located in the Shuttle's payload bay, the other – a critical change from the SIR-C/X-SAR, allowing single-pass interferometry – on the end of a 60-meter (200-foot) mast〔 that extended from the payload bay once the Shuttle was in space. The technique employed is known as interferometric synthetic aperture radar. The elevation models are arranged into tiles, each covering one degree of latitude and one degree of longitude, named according to their south western corners. It follows that "n45e006" stretches from 45°N 6°E to 46°N 7°E and "s45w006" from 45°S 6°W to 44°S 5°W. The resolution of the raw data is one arcsecond (30 m), but this has only been released over United States territory. A derived one arcsecond dataset (with trees and other non-terrain features removed) covering Australia was made available in November 2011; the raw data are restricted for government use. For the rest of the world, only three arcsecond (90 m) data are available. Each one arcsecond tile has 3,601 rows, each consisting of 3,601 16 bit bigendian cells. The dimensions of the three arcsecond tiles are 1201 x 1201. The original SRTM elevations were calculated relative to the WGS84 ellipsoid and then the EGM96 geoid separation values were added to convert to heights relative to the geoid for all the released products. The elevation models derived from the SRTM data are used in geographic information systems. They can be downloaded freely over the Internet, and their file format (.hgt) is widely supported. The Shuttle Radar Topography Mission is an international project spearheaded by the U.S. National Geospatial-Intelligence Agency (NGA) and the U.S. National Aeronautics and Space Administration (NASA). NASA transferred the SRTM payload to the Smithsonian National Air and Space Museum in 2003; the canister, mast, and antenna are now on display at the Steven F. Udvar-Hazy Center in Chantilly, Virginia.〔(【引用サイトリンク】url=http://airandspace.si.edu/collections/artifact.cfm?object=nasm_A20040261000 )〕 == No-data areas == The elevation datasets are affected by mountain and desert no-data areas. These amount to no more than 0.2% of the total area surveyed,〔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 – 'the ‘finished’ grade version of the data (also referred to as Version 2) still contains data voids (some 836,000 km^2)'; 836,000 is 0.164% of the Earth's 5.1×10^8 km^2 surface〕 but can be a problem in areas of very high relief. They affect all summits over 8,000 meters, most summits over 7,000 meters, many Alpine and similar summits and ridges, and many gorges and canyons. There are some SRTM data sources which have filled these data voids, but some of these have used only interpolation from surrounding data, and may therefore be very inaccurate. If the voids are large, or completely cover summit or ridge areas, no interpolation algorithms will give satisfactory results. Other developers, including NASA World Wind and Google Earth, have improved their results by using 1-arc-second for the United States and 3-arc-second for the rest of the world, data in the interpolation process, but, due to the poor resolution of these data, and very poor quality of some of them, they have further improved their earth viewing services by adding data from other sources. Readers with Google Earth software can examine an example of the most recent results by clicking on (Mount Everest) and tilting the image. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Shuttle Radar Topography Mission」の詳細全文を読む スポンサード リンク
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