Characteristics, uses, and sources Introduction to DEMs

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 –ASTER DEM derived from “Advanced Spaceborne Thermal Emission and Reflection Radiometer,” sensor 30m –LiDAR Light Detection and Ranging, high resolution

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

DEM: Characteristics GTOPO DEMSRTM DEM The difference becomes significant at a local level

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 But elevation remains constant over time, right? Think: bodies of water Update, July 2009 !See NEW slides! Update, July 2009 !See NEW slides!

DEM: Characteristics SRTM DEMASTER DEM

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 = m 10m 100m

SRTM DEM: How to Access Select multiple cells Download cells of interest

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

(*) 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

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 sources It is possible to generate a DEM from elevation points gathered through GPS or better yet, contour lines

DEM: Uses A Key input for analysis and modeling –Hydrology –Soil science –Ecosystems –Geology Basis for applications

DEM Uses: Hydrology Rivers and watersheds

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.

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

DEM Uses: Surface Analysis Slope Hillshade Aspect Viewshed Anaglyph

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

DEM Uses: 3D