For the estimation of a dense disparity map from a rectified space-borne stereo image pair and generation of the most qualified digital surface model (DSM), new image matching algorithms are being developed. Our study has two main goals of the DSM quality validation of Worldview-4 (WV-4), which offers the highest ground sampling distance (GSD) (30 cm) of civilian optical space-borne missions together with Worldview-3 (WV-3), and performance comparison of semiglobal matching (SGM) and least squares matching (LSM), two of the most preferred image matching algorithms for space-borne data. In the Istanbul study area with a rough topographic structure, 1 m gridded DSMs were derived from geometrically corrected WV-4 stereo image pairs. The qualities were estimated by well-rounded visual and statistical approaches based on standard deviation and normalized median absolute deviation. In model-to-model comparisons, a very high-resolution airborne laser scanning (ALS) DSM was utilized as the reference model. The results demonstrated that the WV-4 DSM derived by SGM has the standard deviation of ±0.51 m (1.7 GSD) in height in open areas, whereas the LSM DSM has ±1.46 m. In addition, the visual quality of SGM is much better than LSM through building description potential.
Airborne laser scanning (ALS) is one of the most effective remote sensing technologies providing precise three-dimensional (3-D) dense point clouds. A large-size ALS digital surface model (DSM) covering the whole Istanbul province was analyzed by point-based and model-based comprehensive statistical approaches. Point-based analysis was performed using checkpoints on flat areas. Model-based approaches were implemented in two steps as strip to strip comparing overlapping ALS DSMs individually in three subareas and comparing the merged ALS DSMs with terrestrial laser scanning (TLS) DSMs in four other subareas. In the model-based approach, the standard deviation of height and normalized median absolute deviation were used as the accuracy indicators combined with the dependency of terrain inclination. The results demonstrate that terrain roughness has a strong impact on the vertical accuracy of ALS DSMs. From the relative horizontal shifts determined and partially improved by merging the overlapping strips and comparison of the ALS, and the TLS, data were found not to be negligible. The analysis of ALS DSM in relation to TLS DSM allowed us to determine the characteristics of the DSM in detail.
Nowadays, the number and capacity of very high resolution optical satellites grows permanently, so the access to very high resolution space images is not any more a problem. The use of Geographic Information Systems (GISs) together with Remote Sensing became important. With the increased ground resolution a competition to aerial images exist. For the generation of topographic maps, today available as GIS, the accuracy and the information content - what elements can be identified in the image - are important. Both may limit the presentation scale of topographic maps. As horizontal accuracy 0.25mm up to 0.3mm in the map scale are accepted. The required information content is more complicate. The object details to be presented in topographic maps vary from area to area which is based on the planned and unplanned areas. In this study, images from IRS-1C, Kompsat-1, SPOT 5, OrbView-3, IKONOS, QuickBird and WorldView-1 have been used for topographic mapping. For this reason, Zonguldak test fields are an important area for applications of the high resolution imageries. The details which can be identified in the space images dominantly depends upon the ground resolution, available as ground sampling distance (GSD). In this study, high resolution imageries have been tested depending on the GSD and corresponding to the map scales for updating GIS database.
Advancements in the geometric resolution of space images have improved the conditions for generations of large-scale topographic maps. Using WorldView-1, WorldView-2, and GeoEye-1, images can now be captured from space with a 0.5 m ground sampling distance (GSD). Geometric accuracy and information content are the most significant components of mapping from space images. Depending on the resolution, image quality, and shadows, the identification and classification of ground objects may prove challenging. In this research, the geometric accuracy and information content, of panchromatic WorldView-1 images, were analyzed by covering parts of Istanbul and Zonguldak in Turkey. Each of these locations has various topographic characteristics. For the orientation and investigation of the geometric accuracies of images, a number of ground control points (GCPs) were developed as independent checkpoints. Based on bias-corrected rational polynomial coefficients with one GCP, a standard deviation of independent checkpoints on the range of one GSD was obtained. The information content of images was analyzed by mapping all buildings, in both test areas, and comparing the results with reference 1/5000 scaled topographic maps. The results verified that the WorldView-1 images can be utilized for generating and updating 1/5000 scaled topographic maps of urban areas.
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