[GRASS-user] NASA to release no cost 30m DEMs with world-wide coverage on 29 June

Michael Barton michael.barton at asu.edu
Fri Jun 26 01:59:09 EDT 2009

See the following announcement. NASA (USA) will release high  
resolution DEM's of the globe, produced from the Terra ASTER  
satellite, at no charge. You can check out the web announcement at <https://lpdaac.usgs.gov/lpdaac/about/news_archive/monday_june_22_20092 
 >. As a Terra ASTER user, I've been using the DEM's for several years  
and found them to be a very good high-resolution (30x30m)  topography  


==================  announcement ====================


Following review of the validation results, METI and NASA have decided  
to jointly release the
ASTER GDEM on June 29, 2009.  Previously, METI and NASA announced  
their intent to
contribute the ASTER GDEM to the Global Earth Observation System of  
Systems (GEOSS).
Upon release, the ASTER GDEM will be available at no charge to users  
worldwide via
electronic download from ERSDAC and from NASA’s Land Processes  
Distributed Active
Archive Center (LP DAAC) by visiting http://www.gdem.aster.ersdac.or.jp/
and https://wist.echo.nasa.gov/~wist/api/imswelcome/, respectively.

The ASTER instrument was built by METI and launched onboard NASA’s  
Terra spacecraft in
December 1999.  The ASTER instrument uses the nadir-viewing and the  
telescopes; together they enable along-track stereoscopic capability  
to generate stereo data with
a base-to-height ratio of 0.6.  The spatial resolution is 15 m in the  
horizontal plane.  One nadir-
looking ASTER VNIR scene consists of 4,100 samples by 4,200 lines,  
corresponding to about
60 km-by-60 km ground area.

The methodology used to produce the ASTER GDEM involved automated  
processing of the
entire 1.5-million-scene ASTER archive, including stereo-correlation  
to produce 1,264,118
individual scene-based ASTER DEMs, cloud masking to remove cloudy  
pixels, stacking all
cloud-screened DEMs, removing residual bad values and outliers,  
averaging selected data to
create final pixel values, and then correcting residual anomalies  
before partitioning the data into
1°-by-1° tiles.  It took approximately one year to complete production  
of the beta version of the
ASTER GDEM using a fully automated approach.

The ASTER GDEM covers land surfaces between 83°N and 83°S and is  
composed of 22,600
1°-by-1° tiles.  Tiles that contain at least 0.01% land area are  
included.  The ASTER GDEM is
in GeoTIFF with geographic lat/long coordinates and a 1 arc-second (30  
m) grid of elevation
postings.  GDEM is referenced to the WGS84/EGM96 geoid.  Pre- 
production estimated
accuracies for this global product were 20 meters at 95% confidence  
for vertical data and 30
meters at 95 % confidence for horizontal data.  Initial validation  
studies concluded that the
ASTER GDEM generally meets the pre-production accuracy predictions,  
but results do vary
and include areas where GDEM accuracy does not meet the pre-production  

Land surface topography is one of the most fundamental geophysical  
measurements of the
Earth, and it is a dominant controlling factor in virtually all  
physical processes that occur on the
land surface.  Land surface topography also significantly controls  
processes within the
overlying atmosphere and reflects the processes within the underlying  
Consequently, topographic information is important across the full  
spectrum of earth sciences,
and the availability of an up-to-date, high resolution (1-arc-sec or  
less) global DEM remains a
priority of earth scientists for a long time.  The ASTER GDEM is  
expected to meet the
requirements of many users for global topographic information.


C. Michael Barton, Professor of Anthropology
Director of Graduate Studies, School of Human Evolution & Social Change
Director, Center for Social Dynamics & Complexity
Arizona State University

Phone: 480-965-6262
Fax: 480-965-7671
www: <www.public.asu.edu/~cmbarton>

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