Generation and Validation of High‐Resolution DEMs from Worldview‐2 Stereo Data

Abstract

WorldView-2 (WV-2), whose panchromatic images have a 0Á5 m ground sampling distance (GSD), was launched by DigitalGlobe in 2009. It is the first commercial satellite to offer 8-band multispectral imagery with 1Á8 m resolution. Due to the offnadir sensor rotation of WV-2, it is feasible to obtain stereo coverage. Digital elevation models (DEMs) have been created with three WV-2 stereopairs of northern Istanbul with different land types and one of these is comprehensively analysed in this study. A reference DEM, developed from large-scale aerial photogrammetric mapping, together with a lidar DEM and an overlapping neighbouring WV-2 DEM, are used for validation. The generated WV-2 DEM reached, after filtering and in open areas, a standard deviation in height of approximately 1Á0 GSD. A higher number of discrepancies larger than 4 m exist than would be expected from a normal distribution, influencing the standard deviation more than the normalised median absolute deviation (NMAD). ). Before the development of spaceborne imaging technologies, land surveying techniques and photogrammetry were the only approaches that were available for DEM generation. These techniques yield high accuracy but are time consuming. In addition, in some countries the use of aerial images is restricted. Today, optical satellite images compete with aerial images for mapping applications.The elevation models must conform to predetermined quality standards and user requirements. The quality of the model includes two main components: accuracy and morphologic detail. Accurate elevation information is crucial for mapping products if satellite data are to be used (Li, 1998). Based on optical space images, the accuracy of the generated DEMs is mainly dependent upon the ground resolution, base-to-height ratio, image contrast and terrain roughness (Jacobsen, 2003). IKONOS, QuickBird, OrbView, WorldView-1 (WV-1), GeoEye-1 and WorldView-2 (WV-2) as well as Pleiades were launched sequentially and are capable of providing a ground resolution of up to 0Á5m.The automated DEM generation from WV-2 stereopairs in Istanbul, Turkey, is described and analysed. The next section presents the characteristics of the study area and the applied WV-2 dataset. This is followed by an explanation of the methodology used for DEM generation, including scene orientation and matching, digital surface model (DSM) generation, DSM to DEM conversion by filtering, and gap filling. Next, the DEM evaluation process and results are presented, followed by the conclusions from this research. Study Area and WorldView-2 DatasetThe study area is located north-west of Istanbul, Turkey; it is adjacent to the Black Sea coast with the Bosporus at the eastern limit of the site (Fig. 1). The terrain is flat to undulating, with a few steeper parts (Fig. 2); it includes forests, water bodies, partially worked quarries and gravel pits. The height of the terrain ranges from -43 m, due to opencast mining, to 165 m. Fig. 1 shows an overlay of the three WV-2 pan-sharpened scenes used in this study and ...

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