On May 24, 2006, the LP DAAC started offering ASTER Digital Elevation Model (DEM) products using new production software. The new ASTER DEM products are generated without using ground control points (GCPs), and they replace both the existing relative and absolute DEM products. As a result, the LP DAAC no longer offers an absolute DEM product. These 30-meter DEM products are delivered in GeoTif format and are disseminated via the FTP-Pull process only. The new DEM product offered by the DAAC meets or exceeds accuracy specifications set for the ASTER relative DEM product by the ASTER DEM Algorithm Theoretical Basis Document (ATBD). The DAAC's ASTER DEM generation throughput is expected to increase substantially with this new implementation.
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Since April 2001, the LP DAAC has offered a digital elevation model (DEM) produced from ASTER Level-1A data as a standard data product. Two versions of the product were available: a relative DEM, production of which required no ground control points (GCPs), and an absolute DEM, which required user-supplied GCPs. Unlike other ASTER standard data product generation systems, the DEM generation system was designed to produce only one or two DEMs per day. The ASTER DEMs were the only higher-level products that were archived and available for ordering by all users.
The ASTER relative DEM turned out to be one of the most popular ASTER data products among users, and the backlog of orders for that product grew very large. In addition, the LP DAAC became aware of an apparent degradation in the accuracy of its ASTER relative DEM over time.
In late 2005, the decision was made to change the ASTER DEM production software at the LP DAAC. That decision followed an extensive assessment of the accuracy of ASTER relative DEMs produced by a variety of ASTER DEM generation software, and was made in response to a desire by NASA management to increase the rate of ASTER DEM production at the LP DAAC. The new software implemented and released on May 24, 2006 has the capability to produce 50 or more ASTER relative DEMs per day in batch mode operation. The accuracy of the new DEMs meets or exceeds accuracy specifications set for the ASTER relative DEMs by the applicable Algorithm Theoretical Basis Document (ATBD). Validation testing has shown that DEMs produced by the new system frequently are more accurate than 25 meters RMSExyz.
In addition to higher production throughput and improved accuracy of the relative DEM, users need to be aware of other important characteristics of ASTER DEM generation at the LP DAAC:
No Absolute DEM. LP DAAC no longer produces an ASTER absolute DEM (i.e., those produced with user-supplied GCPs). Demand for the previously available ASTER absolute DEM was very low, and product accuracies frequently were diminished by poor quality user-supplied GCPs. Users likely will find that the DEMs produced by the new DAAC system have accuracies approaching those specified in the ATBD for absolute DEMs.
Product Differences. Compared to ASTER DEMs previously available from the LP DAAC, users likely will note some differences in ASTER DEMs produced by the new system, because DEMs now are produced automatically, with no manual editing. Larger water bodies are detected and typically have a single value, but they no longer are manually edited. Any failed areas, while infrequent, remain as they occur. Cloudy areas typically appear as bright regions, rather than as manually edited dark areas. For best results and to the extent possible, users are reminded to select high-quality, cloud-free Level-1A data as input for generating DEMs they order.
ASTER DEM Archive Eliminated. The previously existing ASTER DEM archive is no longer available. The ASTER DEM available from the LP DAAC is strictly an on-demand product.
Geodetic Reference. ASTER DEMs produced by the LP DAAC are referenced to the Earth's geoid using the EGM96 geopotential model.
Product Format. ASTER DEMs are available from the LP DAAC in GeoTif format only.
Product Ordering. ASTER DEMs are available from the LP DAAC through the EOS Data Gateway (EDG) as an on-demand product only.
Distribution Media. As an on-demand product, the ASTER DEM is available to users via FTP-Pull only.
Product Cost. The cost of an ASTER DEM remains $80 per product.