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Communication Dans Un Congrès Année : 2021

Expanding and Enhancing the MAVEN/IUVS Stellar Occultation Dataset

Résumé

Stellar Occultation is one of the observation modes of the Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. There have been thirty-nine dedicated stellar occultation campaigns from 24 March 2015 to 19 July 2021 (covering Martian Years 32 to 36) that are executed every 2 to 3 months over the period of 1-2 days. As the stellar signal of ultraviolet (UV) bright star traverses the Martian middle atmosphere, it gets attenuated due to absorption by atmospheric constituents. From the transmission spectra due to such absorption features, stellar occultations measure column abundances of CO2, O2, O3, and the aerosol optical depth, from which are retrieved the local densities and profiles of temperature and pressure in 20 160 km altitude range. Such stellar signals and transmissions may at times be contaminated by dark current, cosmic rays, stray light, and atmospheric emissions. Of all these factors, contamination by stray light is most prevalent and affects ~60% of stellar occultation events so far, i.e., during dayside or bright terminator observations, sunlight is scattered to mid-UV (MUV) channel of IUVS and saturates it while part of this first order stray light contaminates the second order far UV (FUV) channel. FUV (110 190 nm) is crucial for the retrieval of CO2 and O2 below 100 km and for examining the diurnal and seasonal variability of O2 mixing ratio. At present, events with stray light contamination are not processed, therefore resulting in a huge data gap and significant loss of important information and science. ~75% of these unprocessed cases have first order stray light in FUV confined to the altitude range where FUV starlight is fully attenuated. However, a simple background correction in FUV is incapable of removing the strong stray light as this only eliminates the fainter component of stray light that contaminates the stellar signal directly. This work provides a stray light avoidance algorithm for first-order MUV in FUV to enable retrieval of most of these dayside occultation measurements that are otherwise not processed. This will therefore considerably expand the MAVEN/IUVS stellar occultation dataset and give information on how the added data enhances and impacts the analysis and science, thereby improving the stellar occultation data deduction.
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Dates et versions

hal-03744458 , version 1 (02-08-2022)

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Citer

Gupta Sumedha, Loïc Verdier, Sonal K. Jain, Nicholas Schneider, Fayu Jiang, et al.. Expanding and Enhancing the MAVEN/IUVS Stellar Occultation Dataset. AGU Fall Meeting 2021, Dec 2021, New Orleans, United States. ⟨hal-03744458⟩
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