INTAGRAF International Alpine Gravity Field Course ( – , Merano, Italy) Topography and DEM Modelling mountains

Topography 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 DEM TIN: Vector model (Triangulated Irregular Network) INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

Topography 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 DEM Raster model (DEM – Digital Elevation Model) INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

Topography worldwide GEBCOGEBCO Ocean Mapping at Intergovernmental Oceanographic Commission (IOC) 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 1996 Only onshore data, 30 seconds GTOPO30 ftp://edcftp.cr.usgs.gov/pub/data/gtopo30/global/ ftp://edcftp.cr.usgs.gov/pub/data/gtopo30/global/ DVD 78 $ FTP download free of charge SRTMSRTM 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. 11 th - 22 nd FTP download free of charge INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

Different spatial resolution INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

SRTM Most frequently used data set Resolution: 3 (approx. 90 meters) Height levels: 1 m Coordinates (datum) WGS84 Error horizontal (relative): 15 m Error vertical (relative): 6 m available via ftp://e0mss21u.ecs.nasa.gov/srtm/ or – using an input scheme - Data format:.htg or.bil – binary format in files of 1 x 1 degreeftp://e0mss21u.ecs.nasa.gov/srtm/ Contains data gaps -offshore -in water covered areas -in areas of rough topography INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

SRTM – The method I Figures from: 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 II Radar Holograms Radar Image Interferogram + Phase Information + Phase Information Digital Elevation Model INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

SRTM – data gaps 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 by a) interpolation, or b) other data (gtopo30) INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

SRTM - Vertical Error Shaded reliefFlat map (vertical 6 m relative) causes severe problems in areas with flat topography INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

Terrain Correction - Amounts INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

Topographic correction onshore Histogram of topographic reduction values in percent. Values of histogram classes given in m/s 2. INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

Topographic correction offshore Histogram of topographic reduction values in percent. Values of histogram classes given in m/s 2. INTAGRAF 2005 – Sabine Schmidt, Topography and DEM

Terrain Correction - Radius