Pressure Effects on the SEIS‐InSight Instrument, Improvement of Seismic Records, and Characterization of Long Period Atmospheric Waves From Ground Displacements

Abstract

Mars atmospheric pressure variations induce ground displacements through elastic deformations. The various sensors of the InSight mission were designed in order to be able to understand and correct for these ground deformations induced by atmospheric effects. Particular efforts were made, on one hand, to avoid direct pressure and wind effects on the seismometer and, on the other hand, to have a high performance pressure sensor operating in the same frequency range as the seismometer. As a consequence of these technical achievements and the low background seismic noise of Mars, the InSight mission is opening a new science domain in which the ground displacements can be used to perform atmospheric science. This study presents an analysis of pressure and seismic signals and the relations between them. After a short description of the pressure and seismic sensors, we present an analysis of these signals as a function of local time at the InSight location. Then the coherent signals recorded by both pressure and seismic sensors are described and interpreted in terms of atmospheric signals and ground deformation processes. Two different methods to remove the pressure effects recorded by SEIS sensors are presented, and their efficiency is estimated and compared. These decorrelation methods allow the pressure generated noise to be reduced by a factor of 2 during the active day time period. Finally, an analysis of SEIS signals induced by gravity waves demonstrates the interest of ground displacement measurements to characterize their arrival azimuth.

Subsurface Structure at the InSight Landing Site From Compliance Measurements by Seismic and Meteorological Experiments

“…We will thus focus on this limited range, although episodes with high coherence at higher (or lower) frequency are possible and can be individually studied. For a more complete analysis of the coherence and the observed effects of pressure fluctuations, we refer to the companion paper by Garcia et al (2020).…”

“…In section 2, we recall the theoretical formulation describing the seismic signals induced by pressure fluctuations. In section 3, we present the data sets used in this study and two different techniques to retrieve the ground compliance from real data: The compliance is a byproduct of the pressure-decorrelation methods, discussed in more detail in a companion paper by Garcia et al (2020). The resulting compliance profiles are shown, and the uncertainties and limitations were assessed.…”

Martian Infrasound: Numerical Modeling and Analysis of InSight's Data

“…( ) the frequency-dependent atmospheric dynamics' conversion ratio obtained by Garcia et al (2020). Note that the V/P ratios we will call compliance conversion coefficient in the remaining of this paper (which unit is the (m/s)/Pa) can be understood as the inverse of the specific acoustic impedance (given in Pa•s/m).…”

“…Note that the V/P ratios we will call compliance conversion coefficient in the remaining of this paper (which unit is the (m/s)/Pa) can be understood as the inverse of the specific acoustic impedance (given in Pa•s/m). Figure 2 presents the normalized vertical compliance obtained from atmospheric pressure perturbations (Garcia et al, 2020) and its translation into vertical compliance for acoustic waves. Because for the same horizontal wavelength, atmospheric pressure perturbations have a much lower frequency than acoustic waves, the acoustic compliance estimates are provided only above 2 Hz.…”

“…(a) Average values of vertical compliance of atmospheric pressure perturbations normalized to wind speed (in 1/Pa) as a function of frequency (in Hz), estimated through compliance measurements using the VEL outputs of SEIS-VBB sensors(Garcia et al, 2020). (b) Vertical compliance (in (m/s)/Pa) of acoustic waves as a function of frequency (in Hz) by conversion of vertical compliance from atmospheric pressure perturbation to acoustic waves through equation 11.…”