A Numerical Model of the SEIS Leveling System Transfer Matrix and Resonances: Application to SEIS Rotational Seismology and Dynamic Ground Interaction

Abstract

Both sensors of the SEIS instrument (VBBs and SPs) are mounted on the mechanical leveling system (LVL), which has to ensure a level placement on the Martian ground under currently unknown local conditions, and provide the mechanical coupling of the seis-mometers to the ground. We developed a simplified analytical model of the LVL structure in order to reproduce its mechanical behavior by predicting its resonances and transfer function. This model is implemented numerically and allows to estimate the effects of the LVL on the data recorded by the VBBs and SPs on Mars. The model is validated through comparison with the horizontal resonances (between 35 and 50 Hz) observed in laboratory measurements. These modes prove to be highly dependent of the ground horizontal stiffness and torque. For this reason, an inversion study is performed and the results are compared with some experimental measurements of the LVL feet's penetration in a martian regolith analog. This comparison shows that the analytical model can be used to estimate the elastic ground B L. Fayon

Flexible Mode Modelling of the InSight Lander and Consequences for the SEIS Instrument

“…Finally, it should also be mentioned that the levelling structure of SEIS is expected to have resonant modes, and these are likely to be found at ∼30 to 50 Hz depending on the ground properties (Fayon et al 2018). However, as the lander resonances have both horizontal and vertical components, it should be possible to separate them from the levelling structure resonances that are expected to occur on the horizontal components only.…”

“…However, as the lander resonances have both horizontal and vertical components, it should be possible to separate them from the levelling structure resonances that are expected to occur on the horizontal components only. The levelling structure resonances will also provide additional data to further constrain the physical properties of the upper regolith layer at the InSight landing site (Fayon et al 2018).…”

Geology and Physical Properties Investigations by the InSight Lander

“…5.4.1). The high frequency signals also include the transfer function of the leveling system itself when deployed on the ground (Fayon et al 2018). As described in Sect.…”

High Precision SEIS Calibration for the InSight Mission and Its Applications

“…Noise models have already been developed for SEIS in previous studies, such as Lognonné and Mosser (1993), Pou et al (2016), Murdoch et al (2017a,b), Mimoun et al (2017), Fayon et al (2018). However, they were mainly focused on the nominal seismic range of SEIS between 0.01 Hz and 1 Hz (see Fig.…”

“…The leveling structure is mainly made of three legs, each with a linear actuator (LA) to either extend or retract them, supporting a structural ring on which the VBB and SP seismometers are mounted . These legs serve several purposes: getting the sensor assembly level, and providing mechanical coupling with the ground for better seismic recordings (Fayon et al 2018). In this paper, another use of these legs will be made: the possibility to use them to create a tilt, and compare the response of the seismic sensors to this tilt as it would be done with a tilt table.…”