Abstract
Abstract. The geometry of digital height models (DHM) determined with optical satellite stereo combinations depends upon the image orientation, influenced by the satellite camera, the system calibration and attitude registration. As standard these days the image orientation is available in form of rational polynomial coefficients (RPC). Usually a bias correction of the RPC based on ground control points is required. In most cases the bias correction requires affine transformation, sometimes only shifts, in image or object space. For some satellites and some cases, as caused by small base length, such an image orientation does not lead to the possible accuracy of height models. As reported e.g. by Yong-hua et al. 2015 and Zhang et al. 2015, especially the Chinese stereo satellite ZiYuan-3 (ZY-3) has a limited calibration accuracy and just an attitude recording of 4 Hz which may not be satisfying. Zhang et al. 2015 tried to improve the attitude based on the color sensor bands of ZY-3, but the color images are not always available as also detailed satellite orientation information. There is a tendency of systematic deformation at a Pléiades tri-stereo combination with small base length. The small base length enlarges small systematic errors to object space. But also in some other satellite stereo combinations systematic height model errors have been detected. The largest influence is the not satisfying leveling of height models, but also low frequency height deformations can be seen. A tilt of the DHM by theory can be eliminated by ground control points (GCP), but often the GCP accuracy and distribution is not optimal, not allowing a correct leveling of the height model. In addition a model deformation at GCP locations may lead to not optimal DHM leveling. Supported by reference height models better accuracy has been reached. As reference height model the Shuttle Radar Topography Mission (SRTM) digital surface model (DSM) or the new AW3D30 DSM, based on ALOS PRISM images, are satisfying. They allow the leveling and correction of low frequency height errors and lead to satisfying correction of the DSM based on optical satellite images. The potential of DHM generation, influence of systematic model deformation and possibilities of improvement has been investigated.
Highlights
Systematic height model errors by model tilt and low frequency systematic errors often can be seen in height models based on very high resolution optical satellites
Ground control points and a reference digital surface model (DSM) based on aerial photogrammetric survey have been supported by the French National Institute of Geographic and Forest Information (IGN)
For all used data sets the geo-reference is available by rational polynomial coefficients (RPC), presenting the relation between geographic object coordinates and the image positions by the ratio of third order polynomials (Grodecki 2001)
Summary
Systematic height model errors by model tilt and low frequency systematic errors often can be seen in height models based on very high resolution optical satellites. In most cases a not satisfying number and distribution of GCP is available to correct systematic height model errors. Free of charge available reference height models allow a correction of such errors. With the new AW3D30 DSM an improvement against SRTM DSM is available. ALOS PRISM was active from January 2006 up to May 2011, corresponding to this the AW3D30 DSM is more actual as the SRTM DSM based on information from year 2000. An automatic orientation as d’Angelo (2013) describes for large blocks satellite image blocks was not possible in the flat test area Warsaw, in addition low frequency height errors have to be determined and respected for the individual height models. Even if the systematic errors sometimes have only limited influence to the accuracy numbers, it should be respected to avoid local discrepancies
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