Detection, analysis and removal of glitches from InSight's seismic data from Mars

Abstract

The instrument package SEIS (Seismic Experiment for Internal Structure) with the three very broadband and three short-period seismic sensors is installed on the surface on Mars as part of NASA's InSight Discovery mission. When compared to terrestrial installations, SEIS is deployed in a very harsh wind and temperature environment that leads to inevitable degradation of the quality of the recorded data. One ubiquitous artifact in the raw data is an abundance of transient one-sided pulses often accompanied by high-frequency spikes. These pulses, which we term "glitches", can be modeled as the response of the instrument to a step in acceleration, while the spikes can be modeled as the response to a simultaneous step in displacement. We attribute the glitches primarily to SEIS-internal stress relaxations caused by the large temperature variations to which the instrument is exposed during a Martian day. Only a small fraction of glitches correspond to a motion of the SEIS package as a whole caused by minuscule tilts of either the instrument or the ground. In this study, we focus on the analysis of the glitch+spike phenomenon and present how these signals can be automatically detected and removed from SEIS's raw data. As glitches affect many standard seismological analysis methods such as receiver functions, spectral decomposition and source inversions, we anticipate that studies of the Martian seismicity as well as studies of Mars' internal structure should benefit from deglitched seismic data. Plain Language Summary The instrument package SEIS (Seismic Experiment for Internal Structure) with two fully equipped seismometers is installed on the surface of Mars as part of NASA's InSight Discovery mission. When compared to terrestrial installations, SEIS is more exposed to wind and daily temperature changes that leads to inevitable degradation of the quality of the recorded data. One consequence is the occurrence of a specific type of transient noise that we term "glitch". Glitches show up in the recorded data as one-sided pulses and have strong implications for the typical seismic data analysis. Glitches can be understood as step-like changes in the acceleration sensed by the seismometers. We attribute them primarily to SEIS-internal stress relaxations caused by the large temperature variations to which the instrument is exposed during a Martian day. Only a small fraction of glitches correspond to a motion of the whole SEIS instrument. In this study, we focus on the detection and removal of glitches and anticipate

The Polarization of Ambient Noise on Mars

“…Linearly polarized glitches can be clearly identified and they are more abundant during the night as also observed by Scholtz et al. (2020). Signals with elliptical polarization have different patterns at low (0.03–0.3 Hz) and high (0.3–1 Hz) frequencies.…”

“…We observe large amplitudes during the day and much weaker amplitudes at night on the three components. We also see numerous transient signals that are mostly glitches (Lognonne et al., 2020; Scholtz et al., 2020) or dust devils and wind gusts (Banerdt et al., 2020; Kenda et al., 2020; Lognonne et al., 2020).…”

“…We remind the reader that azimuths are measured ±180°. Glitch origin is still under debate (Lognonne et al., 2020; Scholtz et al., 2020). Apart from these signals visible in the entire frequency range, we also observe changes of polarization between day and night and between high and low frequencies.…”

Super High Frequency Events: A New Class of Events Recorded by the InSight Seismometers on Mars

“…Additionally, there are long‐period transient signals (usually below 1 Hz) in the data, that appear as one‐sided pulses in the raw waveform. Termed as glitches, it is understood that these signal are a result of temperature‐related stress relaxation inside SEIS and from the lander (Scholz et al., 2020).…”

High‐Frequency Seismic Events on Mars Observed by InSight

“…The most obvious source for seismic noise is the martian atmosphere, notably wind and pressure fluctuations and their coupling to the InSight lander observed during the sunlit portion of the day (Ceylan et al., 2020; Lognonné et al., 2020). Sol 421 also exhibits bursts of energy visible across a broad band of frequencies that are manifested as vertical bright‐colored lines in Figure 1; these are glitches (Scholz et al., 2020; Lognonné et al., 2020, SI5) that are caused by thermally induced events within the SEIS instrument assembly resulting in a small tilt of the seismometers. Horizontal bands of energy at higher frequencies are wind‐induced spacecraft resonances, and there is an intriguing resonance at around 2.4 Hz that is present at all times, even when the atmospheric background noise is low.…”