The Mastcam‐Z Radiometric Calibration Targets on NASA's Perseverance Rover: Derived Irradiance Time‐Series, Dust Deposition, and Performance Over the First 350 Sols on Mars

Abstract

The Mastcam‐Z radiometric calibration targets mounted on the NASA's Perseverance rover proved to be effective in the calibration of Mastcam‐Z images to reflectance (I/F) over the first 350 sols on Mars. Mastcam‐Z imaged the calibration targets regularly to perform reflectance calibration on multispectral image sets of targets on the Martian surface. For each calibration target image, mean radiance values were extracted for 41 distinct regions of the targets, including patches of color and grayscale materials. Eight strong permanent magnets, placed under the primary target, attracted magnetic dust and repelled it from central surfaces, allowing the extraction of radiance values from eight regions relatively clean from dust. These radiances were combined with reflectances obtained from laboratory measurements, a one‐term linear fit model was applied, and the slopes of the fits were retrieved as estimates of the solar irradiance and used to convert Mastcam‐Z images from radiance to reflectance. Derived irradiance time series are smoothly varying in line with expectations based on the changing Mars‐Sun distance, being only perturbed by a few significant dust events. The deposition of dust on the calibration targets was largely concentrated on the magnets, ensuring a minimal influence of dust on the calibration process. The fraction of sunlight directly hitting the calibration targets was negatively correlated with the atmospheric optical depth, as expected. Further investigation will aim at explaining the origin of a small offset observed in the fit model employed for calibration, and the causes of a yellowing effect affecting one of the calibration targets materials.

Reflectance of Jezero Crater Floor: 2. Mineralogical Interpretation

“…However, unlike the typical dust‐coated rocks or soils, the VIS spectra exhibit only a weak 0.545 μm band and a positive 0.75–0.84 μm spectral slope. Merusi (2022) provide additional multispectral observations of the magnetic dust using Mastcam‐Z data (0.44–1.02 μm). In the IRS data, no clear absorption was observed in the near‐infrared range (Figure 4e).…”

Dust Lifting Through Surface Albedo Changes at Jezero Crater, Mars

“…We note that these values are estimates: the surface is not homogeneous, which allows for large amounts of dust to remain within coarse sands after dust removal events (Greeley et al., 2005; Reiss et al., 2010) and there are albedo spatial variations (albedo changes due to dust removal are difficult to observe on surfaces with similar reflectance such as optically thick dust layers). Furthermore, two‐layer radiative transfer models of dust‐coated surfaces reveal the strong dependence of illumination and observation angles on constraining dust thickness (Johnson, Sohl‐Dickstein, et al., 2006; Johnson et al., 2003, 2004, Kinch et al., 2007, 2015; Merusi et al., 2022), which has not been considered fully here.…”

“…These observations allow the identification of albedo changes by comparing images of the same target acquired under very similar conditions. In addition, they provide information on the spectral reflectance using the blue, green and red Bayer filters, characterized by effective wavelengths of 480, 544, and 630 nm (respectively) and half‐width at half‐maximum values between 41 and 46 nm (Bell et al., 2021; Merusi et al., 2022). From these three reflectance values it is possible to calculate the green Bayer filter band depth in a way analogous to Jacob et al.…”

Regolith of the Crater Floor Units, Jezero Crater, Mars: Textures, Composition, and Implications for Provenance

“…(2020) and Merusi et al. (2022). Additional details about the software tools developed for multispectral data processing tasks can be found in Million et al.…”

“…Variance bars indicate the standard deviation of reflectance values from those pixels on each filter's associated image that fall within the specific region of interest (ROI). Details about the Mastcam-Z onboard calibration targets and their use in generating reflectance factor data can be found in Kinch et al (2020) and Merusi et al (2022). Additional details about the software tools developed for multispectral data processing tasks can be found in Million et al (2022).…”