In this case study, an active runway of a civilian airport in Zonguldak, Turkey was used to assess the suitability of spaceborne digital elevation models (DEMs) to model an anthropogenic structure. The tested DEMs include the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), the Advanced Land Observing Satellite (ALOS) World 3D 30 m (AW3D30), the Shuttle Radar Topography Mission (SRTM)-1”, the SRTM-3”, the SRTM-X, the TanDEM-3”, and the WorldDEMTM. A photogrammetric high accuracy DEM was also available for the tests. As a reference dataset, a line-leveling survey of the runway using a Leica Sprinter 150/150M instrument was performed. The selection of a runway as a testbed for this type of investigation is justified by its unique characteristics, including its flat surface, homogenous surface material, and availability for a ground survey. These characteristics are significant because DEMs over similar structures are free from environment- and target-induced error sources. For our test area, the most accurate DEM was the WorldDEMTM followed by the SRTM-3” and TanDEM-3”, with vertical errors (LE90) equal to 1.291 m, 1.542 m, and 1.56 m, respectively. This investigation uses a method, known as the runway method, for identifying the vertical errors in DEMs.
The tropospheric delay and gradients can be estimated using Global Positioning System (GPS) observations after removing the ionospheric delay, which has been widely used for atmospheric studies and forecasting. However, high-order ionospheric (HOI) delays are generally ignored in GPS processing to estimate atmospheric parameters. In this study, HOI effects on GPS-estimated tropospheric delay and gradients are investigated from two weeks of GPS data in June 2011 at selected GPS stations in Turkey. Results show that HOI effects are up to 6 mm on zenith tropospheric delay (ZTD), 4 mm on the North-South (NS) gradient and 12 mm on the East-West (EW) gradient during this period, but can reach over 30 mm in slant tropospheric delays. Furthermore, the HOI effects on tropospheric delay and gradient are larger in the daytime than the nighttime. Furthermore, HOI effects on tropospheric delay are further investigated on low and high solar activity days. The HOI effects on GPS estimated tropospheric delay and gradients in high solar activity days are higher than those in low solar activity days.
SummaryThe aim of this project was to estimate the accuracy of the Shuttle Radar Topography Mission (SRTM) digital elevation model over the territory of the Republic of Poland, using the centreline cross-sections of runways as reference data. This method is known as the runway method. The statistical investigations were carried out based on the height differences between the SRTM and the reference data. For this purpose, 22 sections of the SRTM with 1 arcsecond of spatial resolution (SRTM-1″) and profiles of 30 runways were used. Data processing was performed using ArcGIS (Esri) software package. The study found that the SRTM-1″ had a -3.65 m magnitude elevation bias. The standard deviation and root-mean-square error (RMSE) of the elevation differences between the SRTM and the reference data reached the level of 1.88 m and 4.14 m, respectively. The obtained results are consistent with the investigations of the SRTM-3″ model conducted by other authors for the area of Poland and other countries. Overall, it can be confirmed that the SRTM-3″ model performs significantly better over flat areas than the SRTM-1″ in terms of RMSE of the vertical accuracy.
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