Modeling acoustic propagation on Mars

It is important to understand how the atmospheric conditions affect the propagation of sound waves on Mars, both for the study of the acoustic sources and of the atmosphere itself. As 3 microphones are already on Mars (2 on NASA/Perseverance and 1 on CNSA/Zhurong) and potentially more to come, a model of the propagation of sound in the Martian surface layer was needed. A first-principle acoustic attenuation model is used to quantify the excess attenuation of the Martian atmosphere. Thanks to inputs extracted from a global circulation model of Mars (the LMD Martian Climate Database), we are able to compare the magnitude of attenuation at different places and times, from 10 Hz to 20 kHz. Propagation effects are also considered by adapting a parabolic equation code to the Martian conditions. This accounts for strong temperature gradients near the surface, as well as gradients of wind speed. The acoustic reflection on the ground assumes a semi-porous medium. The turbulent fluctuations of temperature and wind speed are implemented using the frozen medium approach. The model shows that characteristics of sound waves propagation depend drastically on the local time. It provides a useful framework to interpret acoustic signal recorded on Mars. The model shows that characteristics of sound waves propagation depend drastically on the local time. It provides a useful framework to interpret acoustic signal recorded on Mars.