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Introduction to DEMs

Introduction to DEMs. Characteristics, uses, and sources. DEM. Digital Elevation Model Characteristics Uses Sources. DEM: Sources and Resolutions. Different versions, sources and spatial resolutions GTOPO Global Topographic Data, 30” (~1km) SRTM Shuttle Radar Topography Mission, 90m

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Introduction to DEMs

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  1. Introduction to DEMs Characteristics, uses, and sources

  2. DEM Digital Elevation Model • Characteristics • Uses • Sources

  3. DEM: Sources and Resolutions • Different versions, sources and spatial resolutions • GTOPO • Global Topographic Data, 30” (~1km) • SRTM • Shuttle Radar Topography Mission, 90m • ASTER • DEM derived from “Advanced Spaceborne Thermal Emission and Reflection Radiometer,” sensor 30m • LiDAR • Light Detection and Ranging, high resolution

  4. DEM: Characteristics GTOPO DEM SRTM DEM From a regional perspective, their difference in resolution is almost unnoticeable.

  5. DEM: Characteristics GTOPO DEM SRTM DEM The difference becomes significant at a local level

  6. DEM: Characteristics SRTM DEM 90m resolution Global reach Few vertical errors Not affected by clouds(microwaves travel through the atmosphere) 4 versions– the most recent is the best ASTER DEM 30m resolution Satellite image scene reach Many vertical errors Affected by clouds (optical waves reflect the atmosphere) As many versions as satellite images Update, July 2009 !See NEW slides! But elevation remains constant over time, right? Think: bodies of water

  7. DEM: Characteristics SRTM DEM ASTER DEM ASTER DEM

  8. Quick Lesson in Spatial Resolution • The difference between a spatial resolution of 100m and 10m is not a factor of 10, but a factor of 10² = 100 10m 100m 100m

  9. SRTM DEM: How to Access • http://srtm.csi.cgiar.org • Select multiple cells • Download cells of interest

  10. ASTER DEM: How to Access • Many ways, one example: • Search image and ID in Glovis • Specify DEM when ordering

  11. (*) New ASTER GDEM • ASTER GDEM Readme File – ASTER GDEM Version 1 • The ASTER GDEM (Global Digital Elevation Model) was developed as a joint effort by METI (Ministry of Economy, Trade, and Industry) of Japan and NASA. • METI & NASA provided the ASTER GDEM to the Global Earth Observation System of Systems.

  12. (*) New ASTER GDEM

  13. (*) New ASTER GDEM • ASTER GDEM Readme File – ASTER GDEM Version 1 • “the overall accuracy of the ASTER GDEM, on a global basis, can be taken to be approximately 20 m at 95 % confidence.” (5) • “Some tiles have substantially better than 20 m accuracy, and some tiles have substantially worse than 20 m vertical accuracy.” (6) • Where are there more errors? (5) • Where the number of scenes is low • Persistently cloudy areas • Where there was no alternate DEM • Another point: bodies of water (6) • The elevation of most inland lakes is not constant, and for the most part was not identified.

  14. DEM: In situ sources • It is possible to generate a DEM from elevation points gathered through GPS or better yet, contour lines

  15. DEM: Uses • A Key input for analysis and modeling • Hydrology • Soil science • Ecosystems • Geology • Basis for applications 3D

  16. DEM Uses: Hydrology • Rivers and watersheds

  17. DEM Uses: Soil Science • Pedology • The ground and landscapes influence the origins, formations, classifications, and morphology of the soils. • Edaphology • Soil science dealing with crop production We will look at some uses and similar applications with hydrology and surface tools.

  18. DEM Uses: Ecosystems • Elevation is essential to the identification of different ecosystems, eco-regions, life zones, climate zones, etc.

  19. DEM Uses: Surface Analysis • Slope • Hillshade • Aspect • Viewshed • Anaglyph

  20. DEM Uses: 3D 2D ASTER Image SERVIR-Viz, 3D platform Landsat image mosaic, placed over the surface of a DEM

  21. DEM Uses: 3D

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