INTAGRAFInternational Alpine Gravity Field Course(27.08.2005 – 09.09.2005, Merano, Italy)

Topography and DEMTopography and DEM

Modelling mountains

Topography and DEMTopography and DEM

TIN: Vector model (Triangulated Irregular Network)

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

•History:Official elevation network had to be used for a 3D model,

•Can integrate different sources of data,

•Very flexible, can model even vertical or overhanging topography

Topography and DEMTopography and DEM

TIN: Vector model (Triangulated Irregular Network)

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

Topography and DEMTopography and DEM

Raster model (DEM – Digital Elevation Model)

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

•Data are sorted in a regular, quadratic grid

•Ideal for scan-lines of satellites

•Easy to treat / to implement

BUT

•Contains redundant information in flat areas

can be very large!

Topography and DEMTopography and DEM

Raster model (DEM – Digital Elevation Model)

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

Topography worldwideTopography worldwide

GEBCO Ocean Mapping at Intergovernmental Oceanographic Commission (IOC)

http://www.ngdc.noaa.gov/mgg/gebco/gebco.html

Topography / bathymetry worldwide complete: 1 Minute academic license : 99 pound sterling

GTOPO30 U.S. Geological Survey's EROS Data Center a compilation of different raster and vector sources, completed in 1996Only onshore data, 30 seconds

http://edcdaac.usgs.gov/gtopo30/gtopo30.aspftp://edcftp.cr.usgs.gov/pub/data/gtopo30/global/

DVD 78 $FTP download free of charge

SRTM Shuttle Radar Topography Mission (NASA, U.S.G.S. EROS Data Center ) Only onshore data between 60° N and 56°S, 3 seconds, in the United States 1 second

Satellite mission: Feb. 11th - 22nd 2000

http://srtm.usgs.gov/

FTP download free of chargeINTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

Different spatial resolutionDifferent spatial resolution

11 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 1246

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47

3712 values

G EBCO 1 M inute (ca. 1.8 km )

11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 1246

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14641 va lues

G TO PO 30 30 Seconds (ca. 0.9 km )

11 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 1246

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1442401 values

SRTM 3 Seconds (ca. 90 m )

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

SRTMSRTM

Most frequently used data set

Resolution: 3“ (approx. 90 meters)Height levels: 1 mCoordinates (datum) WGS84Error horizontal (relative): 15 m Error vertical (relative): 6 m available via ftp://e0mss21u.ecs.nasa.gov/srtm/or – using an input scheme - http://seamless.usgs.gov/

Data format: .htg or .bil – binary format in files of 1 x 1 degree

Contains data gaps- offshore- in water covered areas- in areas of rough topography

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

SRTM – The method ISRTM – The method I

Figures from: http://srtm.usgs.gov/

60 m

The fixed baseline interferometry uses the traveltime difference between two radar beams, which are sent to the Earth, reflected at the surface, and then received by two antennas at a distance of 60 m.

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

SRTM – The method IISRTM – The method IIRadar Holograms

Radar ImageRadar Image

Interferogram

+ PhaseInformation

+ PhaseInformation

Digital Elevation Model

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

SRTM – data gapsSRTM – data gaps

11 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 1246

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Data Gaps

(here marked red)exist in areas of rough topography or water covered areas.

cause problems with- visualization- calculation of the topographic correction- volume and/or surface calculations

May be filled bya) interpolation, orb) other data (gtopo30)

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

SRTM - Vertical ErrorSRTM - Vertical Error

10 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 1154

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55

10 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 1154

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55

-40

-30-20-10

010

203040

5060

708090100110120130140150160

Shaded reliefFlat map

(vertical 6 m relative)causes severe problems in areas with flat topography

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

Terrain Correction - AmountsTerrain Correction - Amounts

Topographic Correction [mGal]0 10 20 30 40

0

20

40

60

Southern Andes No:13512 Northern Andes No:12034

Transalp No:468 Meran No:443

Topographic Correction Values in Selected Areas

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

Topographic correction onshoreTopographic correction onshore

-5,25 - -5.00 -4,5 - -4,25 -3,75 - -3,5 -3,0 - -2,75 -2,25 - -2,0 -1,5 - -1,25 -0,75 - 0,5 0 - 0,25

0

10

20

30

40

50

60

Land

Histogram of topographic reduction values in percent. Values of histogram classes given in 10-5 m/s2.

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

Topographic correction offshoreTopographic correction offshore

-70 - -65 -55 - -50 -40 - -35 -25 - -20 -10 - -5 5 - 10 20 - 25 35 - 40 50 - 55 65 - 70

0

5

10

15

20

25

Offshore

Histogram of topographic reduction values in percent. Values of histogram classes given in 10-5 m/s2.

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

15012510075500 25

0

-5

Calculation radius [km]

Topographic correction for 440 stations in Meran area (Alps, Italy):Difference to correction for the radius 167 km.

INTAGRAF 2005 – Sabine Schmidt, “Topography and DEM”

Terrain Correction - RadiusTerrain Correction - Radius