Abstract
The great amount of data that will be produced during the imaging of Mercury by the stereo camera (STC) of the BepiColombo mission needs a compromise with the restrictions imposed by the band downlink that could drastically reduce the duration and frequency of the observations. The implementation of an on-board real time data compression strategy preserving as much information as possible is therefore mandatory. The degradation that image compression might cause to the DTM accuracy is worth to be investigated. During the stereo-validation procedure of the innovative STC imaging system, several image pairs of an anorthosite sample and a modelled piece of concrete have been acquired under different illumination angles. This set of images has been used to test the effects of the compression algorithm (Langevin and Forni, 2000) on the accuracy of the DTM produced by dense image matching. Different configurations taking in account at the same time both the illumination of the surface and the compression ratio, have been considered. The accuracy of the DTMs is evaluated by comparison with a high resolution laser-scan acquisition of the same targets. The error assessment included also an analysis on the image plane indicating the influence of the compression procedure on the image measurements.
Highlights
The STereo Camera (STC) for the ESA BepiColombo mission to Mercury, has been realized with an innovative and compact design in which the light collected independently by two optical channels at ±20° with respect to the nadir direction converges on a unique bi-dimensional detector
The object point precision and accuracy in a stereo DTM depends on several factors: viewing conditions, errors affecting the calibration, image orientation and image measurements (Re et al, 2015)
The first section is devoted to the measure of image compression through a series of image quality parameters analysis while the second part discusses DTM accuracy evaluation and matching performance
Summary
The STereo Camera (STC) for the ESA BepiColombo mission to Mercury, has been realized with an innovative and compact design in which the light collected independently by two optical channels at ±20° with respect to the nadir direction converges on a unique bi-dimensional detector. In preparation for the DTM generation from STC images, several aspects have to be studied in terms of image analysis and from the photogrammetric point of view, especially when the mission constraints (data volume and observation strategies) have to be respected. The quality of the images can be affected by the compression effects that influence indirectly image matching (Robinson et al, 1995; Li et al, 2002). The idea is that, once the influence of the image compression on the 3-dimensional products is known, the possibility to address the observation strategies in terms of compromise between the data volume saving and the quality of the image becomes relevant. The first section is devoted to the measure of image compression through a series of image quality parameters analysis while the second part discusses DTM accuracy evaluation and matching performance
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