Investigation of boresight offsets and co-registration of HiRISE and CTX imagery for precision Mars topographic mapping

Images from two sensors, the High-Resolution Imaging Science Experiment (HiRISE) and the Context Camera (CTX), both on board the Mars Reconnaissance Orbiter, were used to generate Digital Elevation Models (DEMs) of the Martian surface. However, the DEMs generated from the images acquired by these two sensors show discrepancies for various reasons, such as variations in the boresight alignment between the two sensors while flying in the complex environment of space. This paper presents a systematic investigation of the discrepancies between the DEMs generated from the HiRISE and CTX images and further the boresight offsets between the HiRISE and CTX sensors. A bundle adjustment approach is presented for the co-registration of HiRISE and CTX images. The experimental analyses were carried out using eight sets of HiRISE and CTX images collected from different regions. The results indicate that the systematic offsets between the DEMs derived from HiRISE and CTX images reach several hundred meters in object space and dozens of pixels in image space along the north-east direction. After co-registration, the offsets were reduced to about 10 m in object space and to sub-pixel level in image space. From the co-registration results, relatively consistent angular boresight offsets were found, which deviated from the default values. The findings are significant for the synergistic use of HiRISE and CTX images for precision Mars topographic mapping.