On the Single-Station Measurement of Ground-Coupled Airwaves: Discrimination of Martian Infrasound and Assessment of Terrestrial Setups
Résumé
Energy transmissions from atmospheric pressure perturbations to ground motion take various forms, ranging from wave transmission to compliance effects. These phenomena are of utmost importance when studying airwaves in planetary atmospheres, and concerns particularly infrasound and gravity waves. In November of 2018, the InSight mission deployed on Mars the seismic instrument SEIS and the weather station APSS, allowing a continuous monitoring of nearly collocated seismic and pressure data. Thanks to this unprecedented temporal coverage, numerous seismic and atmospheric events are recorded daily, and evidently require a joint study of the coupled ground-atmosphere system.The full-wave software SPECFEM-DG developed at ISAE allows the numerical simulation of the coupled ground-atmosphere system with an excellent accuracy, as of today demonstrated on several comparisons with experimental cases. The well-known seismic module SPECFEM allows the rigorous representation of visco-elastic ground motion, including seismic waves. The atmospheric module accounts for winds, non-linearities, viscosity, and (most importantly for the Martian atmosphere) vibrational attenuation induced by carbon dioxide.In this presentation, we investigate various ground-coupled airwaves, with a focus on the relations between pressure and subsequent ground motion. We will briefly recall the theory of air-to-ground energy transmissions, and present a case study involving numerically simulated ground-coupled airwaves in a Martian setup. We will exhibit the characteristics of observable quantities, detail their sensitivity, and employ this knowledge to examine InSight data during some SEIS events. The effects of CO2 attenuation will be promptly assessed. We will also present data acquired during an artificial seismic experiment on Earth, allowing us to discuss the detectability of ground-coupled airwaves on various soils. We will conclude by suggesting elements and keys to improve collocated seismo-acoustic setups dedicated to recording ground-coupled airwaves.