Freely available global digital elevation models (DEMs) are important inputs for many research fields and applications. During the last decade, several global DEMs have been released based on satellite data. ASTER and SRTM are the most widely used DEMs, but the more recently released, AW3D30, TanDEM-X and MERIT, are being increasingly used. Many researchers have studied the quality of these DEM products in recent years. However, there has been no comprehensive and systematic evaluation of their quality over areas with variable topography and land cover conditions. To provide this comparison, we examined the accuracy of six freely available global DEMs (ASTER, AW3D30, MERIT, TanDEM-X, SRTM, and NASADEM) in four geographic regions with different topographic and land use conditions. We used local high-precision elevation models (Light Detection and Ranging (LiDAR), Pleiades-1A) as reference models and all global models were resampled to reference model resolution (1m). In total, 608 million 1x1 m pixels were analyzed. To estimate the accuracy, we generated error rasters by subtracting each reference model from the corresponding global DEM and calculated descriptive statistics for this difference (e.g., median, mean, root-mean-square error (RMSE)). We also assessed the vertical accuracy as a function of the slope, slope aspect, and land cover. We found that slope had the strongest effect on DEM accuracy, with no relationship for slope aspect. The AW3D30 was the most robust and had the most stable performance in most of the tests and is therefore the best choice for an analysis of multiple geographic regions. SRTM and NASADEM also performed well where available, whereas NASADEM, as a successor of SRTM, showed only slight improvement in comparison to SRTM. MERIT and TanDEM-X also performed well despite their lower spatial resolution.
Abstract. Development movements bring along population movements. Investments in Istanbul make the city of Istanbul even more attractive. With the increasing population, the need for water is increasing day by day. Construction of the 3rd Istanbul Airport within the borders of Terkos Basin, which is one of the important drinking water resources of Istanbul, has caused land use changes in the basin. Geographical Information Systems (GIS) and Remote Sensing techniques have been used to examine this change. The data obtained through Remote Sensing can be easily analyzed in GIS environment.In this study, Landsat 8 satellite images of the years 2013, 2015 and 2020 were preferred in the examination of the temporal change of land use of the Terkos Basin. The satellite images obtained were classified using the controlled classification technique in the Envi program. Satellite images classified for the creation and analysis of land use maps have been transferred to the ArcGIS program. The changes in the classes determined according to the obtained results were examined, and the changes in question were revealed by spatial analysis. Suggestions have been made for the protection of the Terkos drinking water basin and ecosystem, which is extremely important for Istanbul.
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