An integral part of the Land Use Projects work involves the
use of high-resolution biophysical data about the land surface.
Central to this is topographic data, which controls many environmental
processes from climate to biology and to soils. In the past,
our research has used global elevation datasets such as the
GTOPO30 from the United States Geological Survey (USGS),
or digitized cartographic maps and produced high-resolution
digital elevation models (DEMs) for more specific regions.
The release of the Shuttle Radar Topographic Mission (SRTM)
from NASA heralds a new age in the way in which we do research.
We can now work anywhere in the globe and have base topographic
data without the need for lengthy digitalization. Predictive
models which use terrain attributes can also be applied globally,
and is no longer restricted to the coverage of internally
SRTM data will cover the entire globe with a 3 arc second
(approx. 90m) digital elevation model. A 1 arc second data
product also exists, but is not available on general release.
The data is currently available for small regions for download
from the National
Map Seamless Data Distribution System, or is available
for the entire globe from an ftp
site. The vertical error is said to be less than 16m.
of SRTM 90m DEM
data currently being distributed by NASA contains no data
holes where water or heavy shadow prevented the quantification
of elevation. These are generally small holes, which nevertheless
render the data less useful, especially in fields of hydrological
Land Use project, in collaboration with Robert Hijmans (University
of Berkeley) and Andy Nelson (University
of Leeds), have imported the SRTM data, and performed
some processing to fill in these no data. This process involved
the production of contours, and the re-interpolation of these
derived contours back into a DEM. We then used the interpolated
DEM values to fill in the original no data holes from the
crude SRTM data. This was done using Arc/Info and an AML script
which is available for download.
Questions regarding the use of this AML should be directed
to Andy Jarvis.
hole-filled SRTM data is available for download from the Consortium
of Spatial Data (CSI)
website, found at the CGIAR
SRTM Data website. Anyone interested in further information
should contact Andy Jarvis.
of SRTM 90m DEM data
scientists are already using this DEM data. We have performed
an analysis of data quality, comparing in detail 90m SRTM
data with a DEM produced from digitizing a 1:10,000 cartographic
map of the region of Dapa in Valle del Cauca, Colombia. Using
contours alone, we produced a 25m high resolution DEM, and
compared this in absolute and relative terms with the SRTM
data product for the same region. In absolute terms the two
DEMs compare very closely, but it is evident that the 1:10,000
cartographic map still produces greater topographic detail.
The ridges and valleys are more pronounced, and in some cases
small streams are identified in the cartographically produced
DEM which are not recognizable in the SRTM data. Some preliminary
hydrological modeling is made to highlight this, showing that
the topographic index (TOPMODEL) differs somewhat between
DEMs, and fails to pick out some small streams in the SRTM
results of this evaluation are available in detail in a Powerpoint
presentation entitled "Comparison
of SRTM derived DEM vs. topographic map derived DEM in the
region of Dapa, Valle del Cauca, Colombia". The associated
data is also
available in a zip file with an ArcView project file for easy