Constrained Bundle Adjustment of Panoramic Stereo Images for Mars Landing Site Mapping

In Mars exploration missions, high-precision landing-site topographic information is crucial for engineering operations and the achievement of scientific goals. Detailed topographic information of landing sites is usually provided by ground panoramic images acquired by lander or rover stereo cameras. This technology was employed for the 1997 Mars Pathfinder (MPF) mission and will also be used in the current 2003 Mars Exploration Rover (MER) mission. Photogrammetric bundle adjustment is a key technique for achieving high-precision topographic products. This paper presents a special constrained bundle-adjustment method that supports high-precision Mars landing-site mapping. A complete set of constraint equations is derived to model the unique geometric characteristics of the stereo cameras. This constrained bundle adjustment is then applied to the panoramic image network to provide high-precision exterior orientation (EO) parameters of the images as well as ground positions of the tie points. A fast bundleadjustment algorithm is proposed in which two kinds of unknowns (EO parameters and ground positions) are solved iteratively in order to avoid the large-scale matrix computations that would be necessary in a simultaneous adjustment. The method and the software are tested using panoramic lander data obtained from the MPF mission and FIDO (Field Integrated Design & Operations) panoramic rover data acquired on Earth. Test results show that sub-pixel to 1 pixel accuracy can be achieved and that the fast algorithm is more than 100 times faster than the simultaneous solution, yet still provides the same or even better accuracy. Methods for automatic tie point selection and DEM and orthoimage generation are also briefly described. The proposed methods and developed software (with minor modifications) will be used during the 2003 MER mission.