What is the Shuttle Radar Topography Mission (SRTM)?
SRTM was designed to collect three-dimensional measurements
of the Earth's surface to generate a near-global digital
elevation model (DEM). The mission was a cooperative project
between the National Aeronautics and Space Administration
(NASA), the National Geospatial-Intelligence Agency (NGA)
of the U.S. Department of Defense (DoD), and the German and
Italian space agencies.
What technique was used for the mission?
SRTM flew on board the Space Shuttle Endeavour in February
2000 and used an interferometric radar system to map the
topography of Earth's surface. Endeavour was launched in
an orbit with an inclination of 57 degrees which allowed
to map all of the Earth's landmass that lies between
60 degrees North and 56 degrees South.
What are SRTM data?
SRTM data was processed into geographic tiles, each of
which represents one by one degree of latitude and longitude.
A degree of latitude measures 111 kilometers North South,
a degree of longitude measures 111 kilometers East West
or less, decreasing away from the equator. Each tile of this
dataset contains 1201x 1201 samples which is equipollent to a 90 m
grid resolution at equator. All tiles together represent an image
sized 432000 x 139200 pixel.
What are the limitations on the data?
For technical reasons data are only available between 60 degrees North and 56
degrees South latitud. The relative horizontal accuracy is about ± 15 m,
the relative vertical accuracy about ± 6 m. The original data came with
data voids indicating insufficient contrast in the radar data. These data voids
tend to occur over water bodies (lakes, rivers, coast lines, etc.), areas with
snow cover and in mountainous regions.
What are GTOPO30 data?
GTOPO30 is another dataset with a resolution of 43200 x 21600
pixel used to cover regions where srtm data are not available.
Why do some regions of the maps appear
streaky?
Streaky regions denote areas where data voids were extrapolated
or where SRTM data were replaced by the lower resolution GTOPO30
data.
Why do some rivers appear in unnatural
colors or regions look single-colored?
The relief maps are elevation maps, i.e. the coloring does
not reflect the natural colors of scenic objects. Because
one color is used for each ground level, some rivers and
other objects may appear in unnatural colors. Lowland areas
containing only few elevation information appear most likely
single-colored.
Why do some small islands not appear in the dataset?
In some cases the SRTM dataset failed to include small islands, and in other cases
the islands are slightly mispositioned.
Are the pages hosted by the NASA or another institution?
No, the pages are a privat project to present world-wide
relief maps. The original data are available from the USGS server at
ftp://e0srp01u.ecs.nasa.gov/srtm.