Geoscience Reference
In-Depth Information
7.5 The Shuttle Radar Topography Mission SRTM
h e Shuttle Radar Topography Mission (SRTM) was a radar system on board
the Space Shuttle
Endeavour
during an 11-day mission in February 2000
(Farr et al. 2000, 2007). SRTM was an international project spearheaded
by the National Geospatial-Intelligence Agency (NGA) and the National
Aeronautics and Space Administration (NASA). Detailed information on
the SRTM project, including a gallery of images and a user's forum, can be
accessed through the NASA web page:
http://www2.jpl.nasa.gov/srtm/
h e data were processed at the Jet Propulsion Laboratory. h ey are distributed
through the United States Geological Survey's (USGS) National Map Viewer
and Download Platform:
http://viewer.nationalmap.gov/viewer/
Alternatively, the raw data i les can be downloaded from
http://dds.cr.usgs.gov/srtm/
h is directory contains zipped i les of SRTM DEMs from various areas of the
world, processed by the SRTM global processor and sampled at resolutions of
1 arc second (SRTM-1, 30 meter grid) and 3 arc seconds (SRTM-3, 90 meter
grid). As an example we download the 1.7 MB i le
s01e036.hgt.zip
from
http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Africa/
containing SRTM-3 data for the Kenya Rit Valley in East Africa. All elevations
are in meters referenced to the WGS84 EGM96 geoid, as documented at
http://earth-info.nga.mil/GandG/wgs84/index.html
h e name of this i le refers to the longitude and latitude of the lower-let
(southwest) pixel of the tile, i.e., latitude one degree south and longitude
36 degrees east. SRTM-3 data contain 1,201 lines and 1,201 samples, with
similar numbers of overlapping rows and columns. At er having downloaded
and unzipped the i le we save
s01e036.hgt
in our working directory. h e
digital elevation model is provided as 16-bit signed integer data in a simple
binary raster. h e bit order is
big-endian
(Motorola's standard) with the most
signii cant bit i rst. h e data are imported into the workspace using
clear
