In 2000, the SRTM (Shuttle Radar Topography Mission) project spearheaded by the U.S. National Geospatial-Intelligence Agency (NGA) and the U.S. National Aeronautics and Space Administration (NASA) produced the most complete high-resolution digital topographic database of the Earth to date. The radar images were acquired by the shuttle equipped with two radar antennas with a baseline of 60 meters. This technique is well known as Interferometric Synthetic Aperture Radar (IfSAR or InSAR) that produce elevation data derived from the phase differences of radar images. After the mission, the collected data were processed, and a Digital Elevation Model (DEM) with 1×1 arc second resolution between 60 north and south latitudes was created. Thereafter, the first and the corrected second versions of the DEM with 1×1 arc second resolution for the US, 3×3 arc second resolution for the rest of the world have been published on the internet. These DEMs are free of charge to use.
The aim of this project is to create a DEM with 3×3 arc-second-resolution for Turkey. The DEM called Turkish Digital Elevation Model 3 (TSYM3) is based on the the SRTM3 supported with the heights collected from 25K national topographic maps, and the heights obtained by an interpolation technique. The TSYM3 includes nearly 150 million grid points with heights. The error of heights that are referenced to the mean sea level is below 9 m within a confidence level of 90%. The spatial distribution of errors depend largely on the topography, however. The pointwise errors in height can reach up to 20-25m in mountainous areas, but are 3-5 m in flat areas.
The data voids in the SRTM3 caused by signal scattering, reflection, shadowing, etc. are mostly filled with 25K national topographic maps produced by General Command of Mapping. The partial DEMs created by digitizing the contour lines of 25K map sheets -350 sheets- are used for filling clustering data voids. The remaining voids of scattered character are filled by the multiquadric interpolation technique. For this purpose a window with a size of 90×90 arc-seconds are moved within the Turkish territory. Each time voids are searched within the window. If found, a partial multiquadric surface is determined, and missing heights are interpolated.
As a result the final product of the project, the TSYM3, is a base data for a variety of geospatial applications, and is shared with interested users on the project web site.
Keywords: SRTM, Digital Elevation Model, InSAR, Turkish Digital Elevation Model-3 (TRDEM3), 25K topographic maps, Interpolation
| Start: | September 2006 |
| Final: | September 2008 |