From 2D to 3D to 4D: NASA Satellite imagery in 3 and 4 dimensions

From 2D to 3D to 4D:
NASA Satellite imagery in 3 and 4 dimensions

Source: Global Land Cover Facility

College Park, Maryland -- The University of Maryland's Global Land
Cover Facility, one of the world's largest suppliers of free online
satellite data, now distributes user-ready editions of land surface
topography data from NASA's Shuttle Radar Topography Mission (SRTM).
The addition of this data set will allow users to overlay traditional
2D satellite maps on elevation data to achieve a 3D representation of
the world. When used in conjunction with the GLCF's land cover change
data, essentially a 4D representation of the Earth surface through
time can be achieved.

SRTM was an experiment conducted by NASA on the Space Shuttle in
February 2000. "In about ten days, NASA achieved what scientists,
engineers and cartographers had dreamed for a century" says Dr.
Ghassem Asrar, NASA Associate Administrator for Earth Science. "We
benefited from using the vantage point of space to map eighty percent
of Earth's land surface, home to more than 90 percent of Earth's
population, with one instrument. The resulting topographic products
provide the highest precision and spatial resolution elevation data
ever acquired with global coverage. These data are used for mapping,
flood forecasts, city and road planning, scientific research, and many
other societal benefits, and will continue to be used for decades."

Users can retrieve free copies of elevation imagery through the GLCF's
easy online interface. Now anyone, anywhere, can download both SRTM
elevation data and a corresponding high resolution satellite image or
land cover product from the GLCF's large, free archive for most areas
of the Earth's surface. North of 60°N and south of 54°S are not
available for SRTM data.

Ron Birk, Director of NASA's Earth Science Applications Division, says
that "the Global Land Cover Facility is contributing to NASA's mission
'to understand and protect our home planet' by integrating the Landsat
orthorectified images and SRTM land surface topography data into
readily accessible products that can be used by people around the
world for research, education, operations, policy, and exploration."

Staff at the GLCF have taken the SRTM data as provided by the USGS and
converted them into very practical formats, allowing for ease of
integration with traditional Earth observing data. In particular, the
GLCF editions of the SRTM products are available in GeoTIFF, which
most users will find more software-ready and a welcome alternative to
the cumbersome native HDF format. Additionally, the GLCF SRTM files
are available in both the native geographic coordinate system and in
UTM coordinates. The UTM version has been clipped to WRS-2 tiles, so
that all Landsat scenes automatically have an SRTM scene fit to the
same dimensions. The global Landsat coverage ETM+ and TM Landsat
scenes available at the GLCF now have a complimentary SRTM scene of
elevation data available on a scene-by-scene basis.

Several different editions of SRTM data are available at the GLCF.

- The SRTM 1-arc-second product (30m resolution) is available in both
UTM and Geographic coordinates for the United States and its
territories.

- The SRTM 3-arc-second product (90m resolution) is available in both
coordinate systems for the entire world. This is the highest
resolution global elevation product available in the public's domain.

- The SRTM 30-arc-second product is a much improved version of the
widely used GTOPO30 product, essentially an improvement in precision
at the same lower resolution of 1 kilometer, which is sufficient for
many uses. The GLCF provides this collection in geographic tiles and
also as a single file, in geographic coordinates.

The GLCF successfully distributes vast quantities of global Landsat
coverage, including the acclaimed GeoCover product. It was decided
therefore to provide the SRTM data, clipped to match Landsat's WRS-2
tiles as a natural evolution of both data collections. Because WRS-2
tiles occasionally do not occupy their nominal positions, the GLCF
SRTM clips include a 7.5 km buffer around the 'official' WRS-2
coordinates. The 30 meter resolution SRTM edition and the 30 meter
resolution Landsat scenes are an ideal match for both visualization
and modeling operations. The Global Land Cover Facility provides SRTM
data in the same projection and datum as the global Landsat GeoCover
imagery, resulting in a directly interoperable data collection.

The value of SRTM extends beyond Landsat and includes associations
with most other Earth observation imagery, including the Terra MODIS
sensor. Additionally, the SRTM data sets can be used by themselves as
a superior elevation modeling resource. The GLCF provides these
editions of SRTM in formats that are readily accepted by most spatial
software, where they can be used to make drape or hill-shade
visualizations and where they can also be used for more sophisticated
modeling using operations of slope, aspect and contouring. Watershed
analysis, sighting, natural hazards assessment and agricultural
erosion potential are examples of many other procedures possible with
quality elevation data such as SRTM.

Visit the Global Land Cover Facility at http://www.landcover.org/ to
find out more and to download these innovative products. Online
documentation has been provided explaining the transformation process
and crediting the source materials made available through NASA and the
USGS.

The Global Land Cover Facility is a research and information center
located at the University of Maryland Institute for Advanced Computer
Studies. As a member of the Research, Education, and Applications
Solutions Network (REASoN) program, the GLCF is sponsored by NASA's
Office of Earth Science Applications Division, through cooperative
agreement NNG04GC53A. The GLCF appreciates support from NASA for this
and all its activities.

SRTM is an international project spearheaded by the National
Geospatial-Intelligence Agency (NGA) and the National Aeronautics and
Space Administration (NASA). For further details see
http://www2.jpl.nasa.gov/srtm/.

Examples of SRTM imagery are available at
http://www.landcover.org/gallery/srtm.shtml.