Comodulation Analysis of Atmospheric Energy Injection into the Ground Motion at InSight Part 1: The Site Dynamics on Elysium Planitia

The NASA InSight mission has successfully deployed the SEIS experiment on Mars [1]. This experiment consists of the very broad band (VBB) and short period (SP) seismometers along with pressure (APSS) and wind (TWINS) instruments [2].

It has long been known that seismograms are coupled to atmospheric conditions, for example affecting results from the Viking's seismic experiment [3]. We show that the response of the InSight seismometers allows an estimate of the wind speed and direction through the drag equation. We further investigate the environmental coupling to the seismic signals across the full data bandwidth, characterising this as a comodulation between pressure, wind and the ground acceleration energies recorded by SEIS.

Our approach is applied to the unique dataset recorded by the SP sensor at each stage of deployment, on the deck, uncovered on the ground and after final covering by wind and thermal shield. The comparison across these three epochs at our full bandwidth of 100 samples per second enables the characterisation of the coupling and source of the dynamics at the site (e.g. vibrations from the lander) yielding an understanding of the observed features and extraction of near-surface regolith parameters. Furthermore, this can be used to understand future planetary deployments and analyse the potential for noise decorrelation. Our approach is extended to examine site detectivity and seismic event identification in Part 2 of this issue [5].

References:

[1] Lognonné, P., et al. In LPSC, vol. 50. 2019.

[2] Lognonné, P., et al. Space Science Reviews 215, no. 1 (2019):12.

[3] Anderson, D. L., et al. JGR 82, no. 28 (1977):4524-4546.

[4] Pike, W. T., et al. In LPSC, vol. 50. 2019.

[5] Charalambous C., et al. this issue