Fusion of photogrammetric and photoclinometric information for high-resolution DEMs from Mars in-orbit imagery

High-resolution Digital Elevation Models (DEMs) of the Martian surface are instrumental for studying the red planet. The Mars Orbiter Laser Altimeter (MOLA) instrument onboard the Mars Global Surveyor provided global DEM of high vertical resolution but with a limited spatial resolution that is not enough for characterizing small geological objects, normalizing illumination conditions across in-orbit optical images, modeling local meteorology, and other applications. This article addresses the problem of producing DEMs for regions of interest on Mars using available in-orbit imagery, typically ≈1000 km2 in area, while insuring a ≈10 m vertical accuracy and a spatial accuracy which is comparable to that of the imagery. A method is proposed that combines photogrammetric and photoclinometric approaches in order to retain their mutual advantages. According to experiments using Mars Reconnaissance Orbiter Context Camera (CTX) images, the proposed method is indeed able to produce DEMs satisfying the previous requirements, with less artifacts, better surface continuity, and sharper details than the photogrammetric method when it is used alone.