characteristics, uses, and sources introduction to dems
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Characteristics, uses, and Characteristics, uses, and sourcessources
Introduction to DEMsIntroduction to DEMsIntroduction to DEMsIntroduction to DEMs
DEMDEM
Digital Elevation Model
• Characteristics
• Uses
• Sources
DEM: Sources and ResolutionsDEM: 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
DEM: CharacteristicsDEM: Characteristics
GTOPO DEM SRTM DEM
From a regional perspective, their difference in resolution is From a regional perspective, their difference in resolution is almost unnoticeable.almost unnoticeable.
DEM: CharacteristicsDEM: Characteristics
GTOPO DEM SRTM DEM
The difference becomes significant at a local level The difference becomes significant at a local level
DEM: CharacteristicsDEM: 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 imagesBut elevation remains constant over time, right?But elevation remains constant over time, right?
Think: bodies of waterThink: bodies of water
Update, July 2009!See NEW
slides!
Update, July 2009!See NEW
slides!
DEM: CharacteristicsDEM: Characteristics
SRTM DEM ASTER DEMASTER DEM
Quick Lesson in Spatial ResolutionQuick 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
100m100m10m10m
100m100m
SRTM DEM: How to AccessSRTM DEM: How to Access
• http://srtm.csi.cgiar.org
• Select multiple cells
• Download cells of interest
ASTER DEM: How to AccessASTER DEM: How to Access
• Many ways, one example:– Search image and ID in Glovis– Specify DEM when ordering
(*) New ASTER GDEM(*) 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.
(*) New ASTER GDEM(*) New ASTER GDEM
(*) New ASTER GDEM(*) 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.
DEM: In situ sourcesDEM: In situ sources
• It is possible to generate a DEM from elevation points gathered through GPS or better yet, contour lines
DEM: UsesDEM: Uses
• A Key input for analysis and modeling– Hydrology– Soil science– Ecosystems– Geology
• Basis for applications
DEM Uses: HydrologyDEM Uses: Hydrology
• Rivers and watersheds
DEM Uses: Soil ScienceDEM 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.
DEM Uses: EcosystemsDEM Uses: Ecosystems
• Elevation is essential to the identification of different ecosystems, eco-regions, life zones, climate zones, etc.
DEM Uses: Surface AnalysisDEM Uses: Surface Analysis
• Slope• Hillshade• Aspect• Viewshed• Anaglyph
DEM Uses: 3DDEM Uses: 3D
2D ASTER Image SERVIR-Viz, 3D platform
Landsat image mosaic, placed over the surface of a DEM
DEM Uses: 3DDEM Uses: 3D
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