J. J. Berthelier

An Imaging HF GPR Using Stationary Antennas: Experimental Validation Over the Antarctic Ice Sheet

Terrestrial And Planetary Imaging Radar (TAPIR) is an innovative high-frequency ground-penetrating radar (GPR) developed in the frame of the Martian NetLander mission to probe the subsurface down to kilometric depths. Unlike most GPRs, TAPIR is able to image underground reflectors with stationary antennas. In this paper, after a brief presentation of the instrument, we describe the method developed to interpret data collected during the RAdar of NEtlander in Terre Ade acutelie (RANETA) field survey in Antarctica. This method consists of retrieving the direction of arrival of each detected echo through the measurement of five components of the electromagnetic field (the three magnetic components and the horizontal components of the electric field). Thus, both the range and the direction of each individual reflection or diffraction due to the ice-bedrock interface are resolved. We validated this method on finite-difference time-domain numerically simulated data for different subsurface configurations before applying it to RANETA observations. In particular, the irregular topography of the bedrock in two sounding sites was revealed. We discuss the accuracy of our results.

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

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.

Initial results of the Netlander imaging ground‐penetrating radar operated on the Antarctic Ice Shelf

The objective of the Netlander mission was to land 4 small geophysical stations on the surface of Mars to study the deep interior, subsurface, surface and atmosphere of the planet. Included in the payload was a ground penetrating radar (GPR) designed to retrieve not only the distance but also the direction of the reflectors, thus providing a simplified 3D imaging of the subsurface. In this paper we report initial results obtained during the RANETA campaign on the Antarctic ice shelf. Data from two soundings of the ice-bed rock interface are analyzed, demonstrating the capability of the radar to disentangle echoes from different reflecting facets of the bed rock.

The WISDOM Radar: Unveiling the Subsurface Beneath the ExoMars Rover and Identifying the Best Locations for Drilling

Abstract The search for evidence of past or present life on Mars is the principal objective of the 2020 ESA-Roscosmos ExoMars Rover mission. If such evidence is to be found anywhere, it will most likely be in the subsurface, where organic molecules are shielded from the destructive effects of ionizing radiation and atmospheric oxidants. For this reason, the ExoMars Rover mission has been optimized to investigate the subsurface to identify, understand, and sample those locations where conditions for the preservation of evidence of past life are most likely to be found. The Water Ice Subsurface Deposit Observation on Mars (WISDOM) ground-penetrating radar has been designed to provide information about the nature of the shallow subsurface over depth ranging from 3 to 10u2009m (with a vertical resolution of up to 3u2009cm), depending on the dielectric properties of the regolith. This depth range is critical to understanding the geologic evolution stratigraphy and distribution and state of subsurface H2O, which provide important clues in the search for life and the identification of optimal drilling sites for investigation and sampling by the Rovers 2-m drill. WISDOM will help ensure the safety and success of drilling operations by identification of potential hazards that might interfere with retrieval of subsurface samples. Key Words: Ground penetrating radar—Martian shallow subsurface—ExoMars. Astrobiology 17, 565–584.

Ground-penetrating radar of the Netlander mission

We present in the first part the state of development of the laboratory prototype of the GPR which will allow to check the performances of all the sub-systems. Then some results obtained from numerical simulation are shown to demonstrate the radar capabilities and the anticipated characteristics of the detected signal. Simulated data have been used to study the algorithms which will be employed to analyse the observations and some examples of initial results are presented. Initial field measurements are reported.

GPR on Mars NetLander

We present the different aspects of the development of an HF GPR which will be devoted to the characterization of geological structures and the detection of possible water reservoirs under the form of ground ice or even of liquid water on Mars.