An estimation of the electrical characteristics of planetary shallow subsurfaces with TAPIR antennas

Abstract

[1] In the frame of the NETLANDER program, we have developed the Terrestrial And Planetary Investigation by Radar (TAPIR) imaging ground-penetrating radar to explore the Martian subsurface at kilometric depths and search for potential water reservoirs. This instrument which is to operate from a fixed lander is based on a new concept which allows one to image the various underground reflectors by determining the direction of propagation of the reflected waves. The electrical parameters of the shallow subsurface (permittivity and conductivity) need to be known to correctly determine the propagation vector. In addition, these electrical parameters can bring valuable information on the nature of the materials close to the surface. The electric antennas of the radar are 35 m long resistively loaded monopoles that are laid on the ground. Their impedance, measured during a dedicated mode of operation of the radar, depends on the electrical parameters of soil and is used to infer the permittivity and conductivity of the upper layer of the subsurface. This paper presents an experimental and theoretical study of the antenna impedance and shows that the frequency profile of the antenna complex impedance can be used to retrieve the geoelectrical characteristics of the soil. Comparisons between a numerical modeling and in situ measurements have been successfully carried over various soils, showing a very good agreement.

Depth of the Martian cryosphere: Revised estimates and implications for the existence and detection of subpermafrost groundwater

“…While orbital radar sounding investigations, like MARSIS, can conduct a global survey of Mars, at moderate spatial resolution, on a timescale of several years, their sensitivity is necessarily limited by their altitude, relative motion with respect to the planet's surface, and the necessity of having to sound through the Martian ionosphere. In contrast, a radar sounder, operating from a fixed lander, at the same frequency as MARSIS, can achieve a 90 dB improvement in sensitivity by its ability to perform many coherent additions of the reflected signal, which can dramatically improve signal to noise [ Ciarletti et al , 2003; LeGall et al , 2006, 2008]. The trade‐off for this improvement in sensitivity is that areal coverage provided by a sounder on a fixed lander is limited to a single point on the planet's surface (or up to several points, if the sounder is included as part of the payload of a multistation geophysical network [ Berthelier et al , 2003]).…”