Hemispherical Descent Imaging – an Observation Concept Capable of Enabling New Planetary Surface Imaging Opportunities

Planetary surface imaging is an essential source of data for conducting planetary science throughout the solar system. Novel imaging systems and alternatives to the predominant approaches (orbital, flyby and rover-based imaging) can open up new opportunities, both in the possible scientific analyses, and the regions of solar system that can be imaged. Capturing images during descent to a planetary surface is one such alternative, predominantly used for engineering purposes, but also established as having scientific value. Whilst descent cameras typically employ similar designs (a downward-looking narrow-angle camera), this paper performs a novel study of a previously uninterrogated approach to descent imaging – hemispiherical descent imaging utilising a camera with a very wide field of view approximating a whole hemisphere – to understand how it differs and what capabilities it offers. We utilise modelling, emulation and simulation to investigate its unique imaging geometry, imaging cadence implications, 3D surface reconstruction, how its data compare to existing orbital imagery, and the viability of its implementation on real mission scenarios. The concept enables valuable scientific observations from small, low mass probes during descent (both powered and free fall) or aerial flight. The wide field of view and vertically-distributed images provide a large-coverage, multiresolution image set enabling geological analysis at small and large scales, 3D terrain reconstruction, and photometry over a wide range of viewing angles.