PhD Defense by Marco Merusi
Title: The Mastcam-Z Radiometric Calibration Targets on NASA's Perseverance Rover: Derived Irradiance Time-Series, Dust Deposition, and Performance Over the First 670 Sols on Mars.
Abstract: NASA’s Perseverance Mars rover has been exploring its landing site, Jezero crater, studying its geology and carrying out scientific activities with its payload instruments. One of these, the multispectral stereoscopic camera Mastcam-Z, acquired several thousands of images of martian landscapes and rocks in color and through its narrow-band filters that span the visible and near infrared spectrum. Mastcam-Z relies on a set of calibration targets, consisting of color and grayscale ceramic materials and strong permanent magnets, which were used for the conversion of images from the unit of radiance, which can change with time, to reflectance, which is an intrinsic property of each material. Before landing, the preparation phase of the calibration targets consisted in a characterisation of its color and grayscale materials, whose reflectance was measured in laboratory, and the testing of different models from which the optimal calibration procedure was determined. The results from the calibration targets over the first 670 martian days (or sols) of Perseverance on Mars showed that the calibration targets and the adopted calibration procedure were efficient in the conversion of Mastcam-Z images to reflectance. In addition, comparison between sunlit and shadowed regions of the targets was a powerful tool to identify variations in the amount of martian dust suspended in the atmosphere. Such dust deposited over all surfaces and was displaced frequently by the wind, changing the observed reflectance of some regions (especially over the magnets). One interesting open questions from this work regard a small discrepancy in the model used for calibration, an unexpected visual and spectral change in one of the materials, and the development of a model that could correct some deviations in the reflectance calibration occurring when the Sun is very low on the horizon. Further analyses might shed light on these topics and pave the way for this and future rover missions.
Supervisors: Morten Bo Madsen, Kjartan Bergeron Kinch
Assessment committee: Lise Christensen, NBI (Chair); Nicolas Thomas, Physicalisches Institute, University of Bern; David Arge Klevang, DTU Space, Copenhagen.