GPR, a ground‐penetrating radar for the Netlander mission

Abstract

In the coming decade, several missions are planned that will land on the surface of Mars landers or instrumented geophysical stations. Among the scientific objectives of these projects, one of the most important will be to unravel the many unknowns in the geological and hydrological history of the planet. The Netlander mission offers a unique opportunity to explore the interior of Mars, its subsurface, its atmosphere, and its distant environment from four landing sites that will be selected to offer a variety of different geophysical conditions. We have thus proposed to fly on these four landers a ground‐penetrating radar (GPR) to explore the geological characteristics of the subsurface and search for water reservoirs down to a depth which may be sufficient to allow a possible detection of liquid water. We provide in this paper a short description of this radar which is based on a new concept to allow a 3‐D imaging of the subsurface by determining the range and direction of the underground reflectors. In order to access to deep layers, it will operate at a low frequency of 2 MHz. Some results obtained by a numerical modeling of the radar operation in an electromagnetic model of the Martian subsurface are presented in order to illustrate the main capabilities of the radar. In the last section, preliminary results from an initial field test are reported. In addition to its primary goal as a ground‐penetrating radar, the GPR will also be operated on Mars as an ionospheric sounder and, in a passive mode, as a HF receiver to measure the radio‐electric background.

Laboratory investigations into the electromagnetic properties of magnetite/silica mixtures as Martian soil simulants

“…One of the main goals of present and future missions to Mars is the investigation of the subsurface of the planet by means of orbiting or landing Ground Penetrating Radars (GPR) [ Picardi et al , 2004; Seu et al , 2004; Berthelier et al , 2003; Leuschen et al , 2003; Grant et al , 2003; Vannaroni et al , 2004]. Such a technique seems to be particularly suitable to address some of the fundamental scientific queries of Mars history and evolution, like finding and locating water, mapping the stratigraphy of different areas (polar caps, sedimentary deposits, volcanic terrains, etc.…”

Numerical simulation of the operation of the GPR experiment on NETLANDER

“…Finally, it is a three dimensional approach which allows us to represent the exact profiles and nonhomogeneities of the electromagnetic properties of the various subsurface layers down to the scale of the spatial mesh size. In addition to the derivation of a suitable electromagnetic model of the underground which is described by Berthelier et al [2003] and will be briefly recalled in the next section, one of the major tasks is to build a representative model of the electric antennas, taking into account their impedance profile, their coupling with the shallow subsurface and the effects of their mutual cross coupling as well as with the lander structure. In order to properly determine the radiation pattern and the transmitted power, the simulation code describes the mutual interaction between currents and electromagnetic fields at the antenna level to derive the varying electric and magnetic field components along the antenna from which the propagation in the subsurface can be modeled.…”

“…However, for the sake of simplicity, we have considered the case of a lander with two opposite monopoles antennas with the right monopole aligned with the +X axis and the left electric monopole along the −X axis. As shown by Berthelier et al [2003], the right monopole illuminates preferentially the half‐space extending in the direction of the +X axis. In addition, the interfaces are modeled as surfaces extending invariant parallel to the Y axis.…”

“…This is not possible with the GPR on a fixed lander. However, as indicated by Berthelier et al [2003], the GPR includes a permittivity probe to measure the electric permittivity of the superficial layers of the soil. This allows us to deduce the angle of propagation of the reflected wave before it exits from the surface.…”

“…We present in this paper some results obtained in the initial phase of a long‐term effort to build a numerical model of the radar operation on Mars and test dedicated signal‐processing algorithms on the simulated data. The concept of the instrument and its design approach have been described by Berthelier et al [2000] and in a companion paper [ Berthelier et al , 2003]. Only the main characteristics are recalled here, in particular an important feature for the instrument sensitivity: since the GPR will be operated from a fixed location and aims at fixed targets, a large number of coherent integrations can be performed in order to improve the Signal/Noise ratio.…”