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Results from the optical depth imaging campaign of the Mars-2020 Perseverance rover

Presentation #213.09 in the session Martian Aurora, Atmosphere, Winds, and Dust (Poster + Lightning Talk)

Published onOct 23, 2023
Results from the optical depth imaging campaign of the Mars-2020 Perseverance rover

The Perseverance rover, which landed in Jezero crater, Mars, on 19 February 2021, has conducted a diverse atmospheric science investigation. The visible extinction optical depth of the atmosphere is monitored near-daily with two instruments: Mastcam-Z and Skycam, part of the Mars Environmental Dynamics Analyzer’s Radiation and Dust Sensor. Mastcam-Z is an articulating, stereo, multispectral camera system that acquires solar images at red, green, blue, and near-infrared wavelengths. These are calibrated to optical depth using similar methods to prior missions. Skycam is a wide-field sky imager fixed to the deck that can image the Sun twice each Martian solar day (sol) when the Sun passes through a neutral density annulus on its optics. Skycam optical depth is calibrated with reference to Mastcam-Z measurements. Skycam allows the rover to consistently acquire diurnal measurements as it can image without requiring a rover wake-up or precluding other rover activities.

Over the first 1.25 Mars years of the mission, optical-depth imaging has tracked one locally-active regional storm, dust lofting from distant regional storms, and clouds—including the first detection of a scattering halo on Mars. Over solar longitude (Ls) 0-150°, optical depths were moderate, with typical values near 0.4-0.5, but with a dip to 0.2 near the end of the period. The January-2021 regional storm (Ls 153-156°) brought optical depths near 1.3—although images under-sampled the variations within the storm—and damaging winds. After this, optical depths were ~0.6 until typical southern spring and autumn storms brought optical depths >1 for weeks after sols 410 and 576 (Ls 210° and 315°). Clouds were seen in the optical depth record and associated sky images over Ls 40-150° during the aphelion cloud belt season. Mid-morning optical depths have exceeded those in mid-afternoon by ~0.1 throughout the mission.

Skycam has accumulated dust and debris on its optics throughout the mission due to its fixed, zenith-looking position on the rover deck. This has allowed tracking the accumulation and removal of individual grains (whether sand or dust-aggregate), and the frequency of removal and deposition events will be reported with the particle size distribution function.

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