The Mars Rover Perseverance is the first NASA Rover with a ground penetrating radar (GPR) payload, the "Radar Imager for Mars' Subsurface Experiment" (RIMFAX) (Hamran et al., 2020). RIMFAX has continuously sounded the upper tens of meters of the Martian subsurface along the Rover traverse, taking the first in situ observations of the shallow Martian subsurface with its long microwave penetration. In this study, we analyze the first 8 km of data, starting at the Octavia E. Butler landing site, where Perseverance landed on 18 February 2021 (see Figure 1 for a map of the landing site and Rover traverse).Numerous studies with Perseverance instruments have classified the overall surficial geology and mineralogy as igneous (e.g., Farley et al., 2022;Liu et al., 2022;Wiens et al., 2022). The study area is then characterized by the two major formations, Máaz Fm and Séítah Fm. For Máaz Fm, Udry et al. (2022) propose the material to be deposited by different lava flows or less likely pyroclastic flows. Its composition is basaltic to basaltic-andesitic. Spectral variability and morphology of Máaz-outcrops lead to further distinction of the Máaz-subregions, upper and lower Máaz, encompassing the eastern, respectively, southern part, with a transitional zone around the south-eastern tip of Séítah (Horgan et al., 2022). In contrast to Máaz, Séítah is interpreted as an olivine cumulate formed by slow cooling magma (Liu et al., 2022;Wiens et al., 2022). On average, Wiens et al. (2022) found less olivine and lower density in Máaz than Séítah. For the emplacement scenario they proposed either olivine settling in a common cumulate spanning Séítah and Máaz or separate lava flows for Máaz with respective erosional contrasts below. Based on radar reflections, Hamran et al. (2022) show that Séítah is the lowermost stratigraphic unit in the studied area, with Séítah horizons dipping under Máaz in multiple locations in the vicinity of the visible surface boundary between the two formations.

The Tharsis Montes volcanoes on Mars are the source of laterally extensive lava flows and other volcanic deposits generating a complex stratigraphy throughout the Tharsis Volcanic Province. We use SHAllow RADar (SHARAD) and Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) observations in a region northwest of Ascraeus Mons to determine the composition, density, thickness, and spatial distribution of these emplaced volcanic materials. We identified subsurface reflectors along 43 SHARAD and five MARSIS observations. Reflectors in the volcanic plains are interpreted to be sequences of basaltic lava flows with interspersed pyroclastic material, dust, or regolith during a hiatus in activity. Others correspond to the base of three major flow fields. Several plain reflectors were detected by both MARSIS and SHARAD. Other notable reflectors were identified near Ascraeus' flank where lava buried glacially derived sediment. We derived thickness and other material properties for flows using their distinct topographic boundary visible in the radar images. Permittivity ranged from 7.0 to 11.2 corresponding to lava flow densities of 3.20–3.52 g/cm3. Flow thicknesses ranged from 19.8 to 60.2 m. Loss tangents were low for the flow fields ranging from 0.024 to 0.043. Loss tangents in the plains ranged from 0.010 to 0.076. Higher loss tangents correspond to lossier regions that may have higher concentrations of radar absorbing minerals like hematite. Surface roughness controls where reflectors are detected. SHARAD detects the base of three out of the four flow fields in this region with muted surface roughness from dust mantling and erosion.

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: