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The Definitive Merged Global Digital Topographic Data Set

Measurements of the Earth's topography are one of the most fundamental data sources in Earth science. A major advance for topographic mapping was taken with the flight of the Shuttle Radar Topography Mission (SRTM), a joint project of NASA, the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) and Agenzia Spaziale Italiana (A.S.I.) space agencies, and the National Geospatial-Intelligence Agency, to use radar interferometry to map all the planet's topography between ±60° latitude.

The data have been transformed into DEMs, which are now available to the public through NASA's Land Processes Distributed Active Archive Center (LP DAAC) at the U.S. Geological Survey Earth Resources Observation Systems (EROS) Center. SRTM topography has become the most popular data set distributed by EDC, with the number of data downloads far exceeding any other remotely sensed data. Since no subsequent global mapping projects are currently planned the SRTM data will remain as the 'definitive' topographic data set for decades to come.

Its improvement and augmentation by incorporating and combining with other existing NASA topographic data sources would represent a significant enhancement and upgrade in a very cost-effective way. The most notable improvement will be the elimination of data voids, where radar shadowing or extremely low radar echo strength prevented the determination of an elevation measurement. Although rare, these can greatly affect use of the DEMs in applications like hydrology and volcanic hazard mapping. Secondly, although the SRTM data exceed their specifications for vertical accuracy by a factor of three, there are detectable meso-scale trends in the data at the meter level that can affect determination of crucial geophysical parameters like glacier volume and ice sheet changes, important measurements in quantifying global climate change.

Finally, we propose to document and distribute other potentially valuable SRTM data sets, namely the global radar image data and a sample set of raw radar echo data with supporting ancillary data. Therefore we propose to undertake four principle tasks: Undertake a systematic program to combine SRTM data with those from other sensors, principally Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), to fill voids in the DEMs according to a prioritized plan, as well as extend the coverage north of the current 60° latitude limit. Work with the Ice, Cloud,and land Elevation Satellite (ICESat) project team at NASA's Goddard Space Flight Center to combine laser altimeter topographic profiles with SRTM DEMs to produce and distribute enhanced resolution data sets.

Produce documentation, users guides and other supporting information for the existing SRTM image and ancillary data cells, as well as generate image mosaics at multiple scales and distribute them via the world wide web. Generate, document and distribute a standard and representative set of SRTM raw radar echo data, along with the appropriate ancillary tracking and pointing data necessary for users to process the echoes into DEMS using improved algorithms or techniques.

Michael Kobrick, PI, NASA's Jet Propulsion Laboratory

Distributed by NASA"s Land Processes Distributed Active Archive Center

Last Updated: Nov 15, 2017 at 1:15 PM EST