METI and NASA Release the ASTER Global DEM

June 28, 2009
By: LP DAAC

Announcement: METI and NASA Release ASTER Global DEM

The Ministry of Economy, Trade, and Industry (METI) of Japan and the United States National Aeronautics and Space Administration (NASA) today jointly released Version-1 of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM). Previously, METI and NASA announced their intent to contribute the ASTER GDEM to the Global Earth Observation System of Systems (GEOSS). Consequently, the ASTER GDEM is available at no charge to users worldwide via electronic download from the Earth Remote Sensing Data Analysis Center (ERSDAC) of Japan and from NASA’s Land Processes Distributed Active Archive Center (LP DAAC).

The ASTER instrument was built by METI and launched onboard NASA’s Terra spacecraft in December 1999. ASTER’s visible and near-infrared subsystem contains nadir-viewing and backward-viewing telescopes, which together enable its stereoscopic capability to acquire stereo image 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 GeoTIF format with geographic lat/long coordinates and a 1 arc-second (30 m) grid of elevation postings. The GDEM is referenced to the WGS84/EGM96 geoid. The GDEM’s pre-production accuracy estimates were 20 meters at 95% confidence for vertical data, and 30 meters at 95% confidence for horizontal data.

Initial studies to validate and characterize the ASTER GDEM confirm that pre-production accuracy estimates are generally achieved for most of the global land surface, although results do vary, and true accuracies do not meet pre-production estimates for some areas. In addition, ASTER GDEM Version-1 does contain certain residual anomalies and artifacts that affect the product accuracy, and potentially may impede its effective use for certain applications. Consequently, METI and NASA acknowledge that ASTER GDEM Version-1 should serve as an “experimental” or “research grade” product. Nevertheless, they are confident that the ASTER GDEM represents an important contribution to the global earth observation community.

ASTER GDEM tiles are available for electronic download from:

ERSDAC: http://www.gdem.aster.ersdac.or.jp/

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