Abstract
The photogrammetric bundle adjustment of line scanner image data requires a precise description of the time-dependent image orientation. For this task exterior orientation parameters of discrete points are used to model position and viewing direction of a camera trajectory via polynomials. This paper investigates the influence of the distance between these orientation points on the quality of trajectory modeling. A new method adapts the distance along the trajectory to the available image information. Compared to a constant distance as used previously, a better reconstruction of the exterior orientation is possible, especially when image quality changes within a strip. <br><br> In our research we use image strips of the High Resolution Stereo Camera (HRSC), taken to map the Martian surface. Several experiments on the global image data set have been carried out to investigate how the bundle adjustment improves the image orientation, if the new method is employed. For evaluation the forward intersection errors of 3D points derived from HRSC images, as well as their remaining height differences to the MOLA DTM are used. <br><br> In 13.5 % (515 of 3,828) of the image strips, taken during this ongoing mission over the last 12 years, high frequency image distortions were found. Bundle adjustment with a constant orientation point distance was able to reconstruct the orbit in 239 (46.4 %) cases. A variable orientation point distance increased this number to 507 (98.6 %).
Highlights
For the photogrammetric processing of line scanner imagery some characteristic features have to be considered in the geometric modeling
We performed a series of bundle adjustment runs with different numbers of tie points to better understand the general relationships between tie point density, OPD and a resulting mean object point accuracy from an experimental point of view
We improved the concept of orientation points (OP) for modeling the exterior orientation (EO) of line scanner imagery within a bundle adjustment by varying the OPD according to the available image information given by the number of tie points
Summary
For the photogrammetric processing of line scanner imagery some characteristic features have to be considered in the geometric modeling. It is possible to reduce the number of parameters in the model and use interpolated EO values for the majority of image lines. The High Resolution Stereo Camera is the photogrammetric imaging instrument on ESA’s Mars Express mission (Neukum et al, 2004). This multi-line sensor with five panchromatic and four multi-spectral CCD lines was developed by the German Aerospace Center (DLR). Every single strip allows the generation of high resolution digital terrain models (DTMs) (Gwinner et al, 2009), (Heipke et al, 2007) and orthoimages (Gwinner et al, 2010). In the following the mathematical model of the bundle adjustment with its adaptations to the HRSC imagery is described. Conclusions and an outlook on future work are given in the last section
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