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Conference Papers Year : 2021

The acoustic properties of the Mars atmosphere at Jezero crater

Ann Ollila
Franck Montmessin
Thierry Fouchet

Abstract

On February 18, 2021 NASAs Perseverance rover landed in Jezero Crater carrying two microphones operating on the surface of Mars, EDLCAM and Supercam. Therefore, it allows the unique opportunity to observe the atmosphere with continuous recordings and to conduct free-field sound propagation experiments on the Mars atmosphere. Positioned on top of the rovers mast, the Supercam microphone records audible sounds from 20 Hz to 10 kHz that originate from three main sources: the atmosphere (turbulence, wind), the Supercam laser-induced sparks on rocks and other rover sounds, especially the aeroacoustic signal generated by the high-speed rotating blades of the Ingenuity rotorcraft. These sounds spread over the entire frequency domain accessible by the microphone: (i) the turbulence/wind-induced acoustic signal starts from the lowest frequency, continuously up to few hundred Hz depending on the wind activity. It has a decreasing slope consistent with the dissipative regime. (ii) The frequency content of the laser-induced spark lies at higher frequencies (2 - 10 kHz) where it shows destructive interference gaps due to echoes on the mast structure and on nearby rocks. (iii) Rover generated sounds (pump, motor) are often monotonic. For instance, Ingenuity flights are heard at the blades passing frequency of ~84Hz and its first harmonic at 168 Hz. The Supercam microphone is now used daily to capture the diversity and the wealth of these phenomena. This presentation focuses on sound propagation properties of the Mars atmosphere, in particular, the first in situ measurement of the sound speed and acoustic intrinsic attenuation. The average sound speed (~240m/s) along the propagation path is derived from the time of flight of the laser-induced acoustic wave from the ground to the microphone. It is combined with the sound speed measured at the microphone location determined from the destructive interference gap in the spectrum. Then, it gives insights into the high frequency air temperature variations over the first two meters from the ground. Moreover, the evolution of the laser spark amplitude with the distance of the target is used to retrieve an attenuation coefficient between 2 and 10 kHz. At low frequency, the attenuation coefficient is studied with the helicopter tones. It is used to constrain existing models in the literature.
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Dates and versions

obspm-03903801 , version 1 (16-12-2022)

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Baptiste Chide, Sylvestre Maurice, David Mimoun, Naomi Murdoch, Ralph Lorenz, et al.. The acoustic properties of the Mars atmosphere at Jezero crater. AGU Fall Meeting 2021, Dec 2021, Nouvelle-Orléans, United States. ⟨obspm-03903801⟩
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