Radiometric Calibration Targets for the Mastcam-Z Camera on the Mars 2020 Rover Mission

Space Sci Rev (2020) 216:141 https://doi.org/10.1007/s11214-020-00774-8 Radiometric Calibration Targets for the Mastcam-Z Camera on the Mars 2020 Rover Mission K.M. Kinch1 · M.B. Madsen1 · J.F. Bell III2 · J.N. Maki3 · Z.J. Bailey3 · A.G. Hayes4 · O.B. Jensen1 · M. Merusi1 · M.H. Bernt1 · A.N. Sørensen1 · M. Hilverda5 · E. Cloutis6 · D. Applin6 · E. Mateo-Marti7 · J.A. Manrique8 · G. Lopez-Reyes8 · A. Bello-Arufe9 · B.L. Ehlmann3,10 · J. Buz11 · A. Pommerol12 · N. Thomas12 · L. Affolter12 · K.E. Herkenhoff13 · J.R. Johnson14 · M. Rice15 · P. Corlies4 · C. Tate4 · M.A. Caplinger16 · E. Jensen16 · T. Kubacki16 · E. Cisneros2 · K. Paris2 · A. Winhold2 Received: 18 May 2020 / Accepted: 17 November 2020 / Published online: 3 December 2020 © The Author(s) 2020 Abstract The Mastcam-Z Camera is a stereoscopic, multispectral camera with zoom capability on NASA’s Mars-2020 Perseverance rover. The Mastcam-Z relies on a set of two deck-mounted radiometric calibration targets to validate camera performance and to provide an instantaneous estimate of local irradiance and allow conversion of image data to units of reflectance (R∗ or I/F) on a tactical timescale. Here, we describe the heritage, design, and The Mars 2020 Mission Edited by Kenneth A. Farley, Kenneth H. Williford and Kathryn M. Stack B K.M. Kinch 1 Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark 2 School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA 3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA 4 Department of Astronomy, Cornell University, Ithaca, NY, USA 5 The Planetary Society, Pasadena, CA, USA 6 Department of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada 7 Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, Madrid, Spain 8 University of Valladolid, Valladolid, Spain 9 National Space Institute, Technical University of Denmark, Lyngby, Denmark 10 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA 11 Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ, USA 12 Space and Planetary Science Department, Physikalisches Institut, University of Bern, Bern, Switzerland 13 Astrogeology Science Center, United States Geological Survey, Flagstaff, AZ, USA 14 Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA 141 Page 2 of 51 K.M. Kinch et al. optical characterization of these targets and discuss their use during rover operations. The Mastcam-Z primary calibration target inherits features of camera calibration targets on the Mars Exploration Rovers, Phoenix and Mars Science Laboratory missions. This target will be regularly imaged during flight to accompany multispectral observations of the martian surface. The primary target consists of a gold-plated aluminum base, eight strong hollowcylinder Sm2 Co17 alloy permanent magnets mounted in the base, eight ceramic color and grayscale patches mounted over the magnets, four concentric, ceramic grayscale rings and a central aluminum shadow post (gnomon) painted with an IR-black paint. The magnets are expected to keep the central area of each patch relatively free of Martian aeolian dust. The Mastcam-Z secondary calibration target is a simple angled aluminum shelf carrying seven vertically mounted ceramic color and grayscale chips and seven identical, but horizontally mounted ceramic chips. The secondary target is intended to augment and validate the calibration-related information derived from the primary target. The Mastcam-Z radiometric calibration targets are critically important to achieving Mastcam-Z science objectives for spectroscopy and photometric properties. 1 Introduction NASA’s Mars 2020 Perseverance Rover mission (Farley et al. 2020, this issue) will launch for Mars in July 2020 and land in Jezero Crater in February of 2021. The Mastcam-Z Camera (Bell et al. 2020, this issue) is a stereoscopic, multispectral camera with zoom capability and is mounted on the rover mast. Mastcam-Z relies on a set of radiometric calibration targets to provide an instantaneous estimate of local illumination conditions and thus convert images of the Martian surface from units of radiance (the instrument observable) to units of reflectance (the material property) on a tactical timescale. There are two targets, the primary and the secondary Mastcam-Z radiometric calibration targets. Both are mounted on the rover deck and viewable from Mastcam-Z. Both targets were designed, built and delivered by the Niels Bohr Institute of the University of Copenhagen. In this manuscript we describe in detail the design and characterization of the targets, and discuss the plans for operational imaging of the targets and processing of such images for the purpose of generating in-flight reflectance (I/F)-calibrated Mastcam-Z image products. This manuscript is part of a set of 3 papers describing the Mastcam-Z investigation. The paper by Bell et al. (2020, this issue) gives an overview of the Mastcam-Z investigation, its goals and components while the paper by Hayes et al. (2020, this issue) describes in detail the pre-flight calibration and performance of the flight Mastcam-Z instrument. Section 2 describes briefly the Mars 2020 mission and Mastcam-Z instrument, gives a more detailed overview of the purpose of the calibration targets and describes their extensive heritage from previous missions. Section 3 describes the design of the two targets. Section 4 presents data from pre-flight spectroscopic characterization of assembled targets as well as “witness samples” of the color and grayscale reference materials embedded in the targets. Section 5 discusses in-flight use of the targets as well as the process for generating in-flight reflectance-calibrated (I/F) Mastcam-Z image products, and Secton 6 gives a summary. Appendix A describes the materials and methods used for construction of more than 20 calibration target units produced (engineering models, flight units, flight spares, display models and “calibration” units). Appendix B describes the testing procedures and results from the dynamical and thermal test programs. 15 College of Science and Engineering, Western Washington University, Bellingham, WA, USA 16 Malin Space Science Systems, San Diego, CA, USA Radiometric Calibration Targets for the Mastcam-Z Camera. . . Page 3 of 51 141 Fig. 1 (a) Pancam calibration target on the Mars Exploration Rover (MER) Spirit, sol 711, sweep magnet visible to the right of the main target. (b) One of three Surface Stereo Imager calibration targets on the Phoenix lander, sol 106. (c) The Mastcam calibration target on the Mars Science Laboratory (MSL) rover, sol 705 2 Background 2.1 Mars 2020 and Mastcam-Z NASA’s Perseverance Rover (Farley et al. 2020, this issue) is a large rover similar to the currently active “Curiosity” rover (e.g., Grotzinger et al. 2014, and 2015). A central (...truncated)