An acoustic investigation of the near-surface turbulence on Mars

Baptiste Chide; Philippe Blanc-Benon; Tanguy Bertrand; Xavier Jacob; Jérémie Lasue; Ralph D Lorenz; Franck Montmessin; Naomi Murdoch; Jorge Pla-Garcia; Fabian Seel; Susanne Schröder; Alexander E Stott; Manuel de la Torre Juarez; Roger C Wiens

doi:10.1121/10.0024347

An acoustic investigation of the near-surface turbulence on Mars

J Acoust Soc Am. 2024 Jan 1;155(1):420-435. doi: 10.1121/10.0024347.

Authors

Affiliations

¹ Space and Planetary Exploration Team, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
² Laboratoire de Mécanique des Fluides et d'Acoustique, Centre National de la Recherche Scientifique, Ecole Centrale de Lyon, Institut National des sciences appliquées Lyon, Université Lyon 1, Ecully, France.
³ Laboratoire d'études spatiales et d'instrumentation en astrophysique, Observatoire de Paris, Université Paris Sciences & Lettres, Sorbonne Université, Centre National de la Recherche Scientifique, Meudon, France.
⁴ Institut de Mécanique des Fluides de Toulouse, Université Toulouse 3, Institut National Polytechnique, Centre National de la Recherche Scientifique, Toulouse, France.
⁵ Institut de Recherche en Astrophysique et Planétologie, Université Toulouse 3, Centre National de la Recherche Scientifique, Centre National d'Etudes Spatiales, Toulouse, France.
⁶ Space Exploration Sector, Johns Hopkins Applied Physics Laboratory, Laurel, Maryland 20723, USA.
⁷ Laboratoire Atmosphères Observations Spatiales, Centre National de la Recherche Scientifique, Université Saint-Quentin-en-Yvelines, Sorbonne Université, Guyancourt, France.
⁸ Institut Supérieur de l'Aeronautique et de l'Espace, Université de Toulouse, Toulouse, France.
⁹ Centro de Astrobiologia, Madrid, Spain.
¹⁰ Institute of Optical Sensor Systems, German Aerospace Center, Berlin, Germany.
¹¹ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
¹² Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana 47907, USA.

PMID: 38240669
DOI: 10.1121/10.0024347

Abstract

The Perseverance rover is carrying out an original acoustic experiment on Mars: the SuperCam microphone records the spherical acoustic waves generated by laser sparks at distances from 2 m to more than 8 m. These N-shaped acoustic waves scatter from the multiple local heterogeneities of the turbulent atmosphere. Therefore, large and random fluctuations of sound travel time and intensity develop as the waves cross the medium. The variances of the travel times and the scintillation index (normalized variance of the sound intensity) are studied within the mathematical formalism of the propagation of spherical acoustic waves through thermal turbulence to infer statistical properties of the Mars atmospheric temperature fluctuation field. The comparison with the theory is made by simplifying assumptions that do not include wind fluctuations and diffraction effects. Two Earth years (about one Martian year) of observations acquired during the maximum convective period (10:00-14:00 Mars local time) show a good agreement between the dataset and the formalism: the travel time variance diverges from the linear Chernov solution exactly where the density of occurrence of the first caustic reaches its maximum. Moreover, on average, waves travel faster than the mean speed of sound due to a fast path effect, which is also observed on Earth. To account for the distribution of turbulent eddies, several power spectra are tested and the best match to observation is obtained with a generalized von Karman spectrum with a shallower slope than the Kolmogorov cascade, ϕ(k)∝(1+k2L2)-4/3. It is associated with an outer scale of turbulence, L, of 11 cm at 2 m above the surface and a standard deviation of 6 K over 9 s for the temperature. These near-surface atmospheric properties are consistent with a weak to moderate wave scattering regime around noon with little saturation. Overall, this study presents an innovative and promising methodology to probe the near-surface atmospheric turbulence on Mars.