Practical Stereophotoclinometry for Modeling Shape and Topography on Planetary Missions

Stereophotoclinometry (SPC) is a technique to extract topographic information from images acquired by spacecraft. It combines stereophotogrammetry and photoclinometry to produce a product that has the accuracy of stereo with the resolution of photoclinometry without the restrictions common to both. We describe the implementation of this technique in the context of digital terrain model (DTM) generation for a small-body mission. We detail the process and the data used to generate SPC-derived DTMs at progressively increasing resolutions. The highest-quality DTMs are generated using four images optimized for topography, a 30° emission angle with the emission azimuth (spacecraft position) to the north, east, south, and west of the target, and one image optimized for albedo (a low incidence angle such that most of the image pixels’ digital numbers are based upon albedo rather than topography). We discuss implications for mission planning and how SPC-based DTM generation can support spacecraft navigation. As a case study, we share outcomes from the modeling performed for the OSIRIS-REx mission to asteroid Bennu.