Radar Attenuation in the Shallow Martian Subsurface: RIMFAX Time‐Frequency Analysis and Constant‐Q Characterization Over Jezero Crater Floor

Abstract

During the first 379 sols of NASA's Perseverance rover mission on Mars, over 5 km had been driven over the Jezero Crater Floor. The rover had gone from the Octavia E. Butler landing site (OEB), located on the relatively flat terrain of the Máaz Formation, to the distinct rugged exposures of the Séítah Formation. Afterward, the rover drove back again to OEB, largely backtracking its original route. The Radar Imager for Mars' Subsurface Exploration (RIMFAX;Hamran et al., 2020) conducted measurements along the whole traverse, providing an exceptional data set for constraining subsurface parameters over a large geographical area spanning several different regions (Figure 1). Moreover, the close vicinity of the two passes allows for testing replicability of obtained media parameters.The first look into the shallow Martian subsurface disclosed intriguing reflector geometries, which at places can be correlated with outcropping rock formations on the surface (Hamran et al., 2022). Yet, more information is contained in the acquired data, hidden by randomly distributed reflections dominating the radar image. This calls for supplementary analysis of the radar data beyond that of visual inspection.Ground-penetrating radar (GPR) data is strongly affected by the frequency dependent attenuation mechanisms. In general, higher frequency content is attenuated more than lower, so that subsurface reflection spectra will be altered compared to that of the transmitted waveform. The constant-Q factor was originally used to describe similar behavior of seismic waves due to cumulative attenuating effects in the ground (Richards & Aki, 1980), but it has also been found applicable for electromagnetic propagation in natural soil and rocks over the GPR frequency range 0.1-1.0 GHz (Harbi & McMechan, 2012;Turner & Siggins, 1994). For this reason, it can be appropriate to assume a linear frequency dependence for the attenuation in GPR sounding:

RIMFAX Ground Penetrating Radar Reveals Dielectric Permittivity and Rock Density of Shallow Martian Subsurface

“…A homogeneous subsurface interpretation is in‐line with results from Eide, Casademont, Berger, et al. (2022), whose radar wave attenuation measurements demonstrate this across the first 379 sols.…”

“…Another governing material parameter in this context is the radar wave attenuation, which is analyzed for this study area by Eide, Casademont, Berger, et al. (2022) and is not regarded here.…”

“…Both permittivity and density help to constrain the subsurface material and bulk consistency, and therefore contribute to determining the geologic composition of the Jezero Crater floor subsurface. Another governing material parameter in this context is the radar wave attenuation, which is analyzed for this study area by Eide, Casademont, Berger, et al (2022) and is not regarded here.…”

Assessing Radar Attenuation in RIMFAX Soundings at the Jezero Western Fan Front, Mars

“…The CFS method (Quan & Harris, 1997) is employed as in Eide et al (2022). A single estimate of the Q*-factor can be derived analytically from the slope Δf c /Δt, which is a best-fit to the change in center frequency f c in the time-frequency spectra of a recording:…”

PyBWE: Python tools for Bandwidth Extrapolation of planetary radar signals

“…• The improvement of the WISDOM (ExoMars, ESA) Ground Penetrating Radar soundings in preparation of the Rosalind Franklin rover mission (Oudart et al, 2021) • The improvement of the MARSIS (Mars Express, ESA) radar sounder resolution by a factor of 6 using both BWE and BWI between different frequency band modes (Gambacorta et al, 2022) • The EMI removal by BWI helped the estimation of attenuations in the Martian subsurface with the RIMFAX (Mars 2020, NASA) Ground Penetrating Radar data (Eide et al, 2022) However, the planetary science community has few radar experts, and to our knowledge no open-source integrated BWE solutions existed before the release of this library, limiting the planetary radar application of this technique. For this reason, we propose in this library integrated BWE solutions for all planetary scientists, as well as the individual functions for planetary radar experts.…”