Characteristics, uses, Characteristics, uses, and sources and sources Introduction to DEMs Introduction to DEMs
Jan 15, 2016
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