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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. E4, 8030, doi:10.1029/2002JE001871, 2003

Local geoelectrical models of the Martian subsurface for shallow

groundwater detection using sounding radars

E. Heggy,1,2 P. Paillou,1 F. Costard,3 N. Mangold,3 G. Ruffie,4 F. Demontoux,4

G. Grandjean,5 and J. M. Malezieux6

Received 15 February 2002; revised 20 July 2002; accepted 28 August 2002; published 6 March 2003.

[1] Low-frequency sounding radars should be able to probe the Martian subsurface layers

down to varying depths, depending on the geoelectrical properties of the sounded sites.

We present in this work four frequency-dependent geoelectrical models of the Martian

subsurface in the 1 20 MHz frequency band, based on laboratory electromagnetic

characterization of Martian soil analogues. Those models correspond to local Martian sites

that we considered to be of particular interest in the search for water using mainly the

Ground-Penetrating Radar (GPR) instrument of the Netlander mission. Results and

discussion are also valid for both sounding experiments MARSIS and SHARAD. The four

models of the Martian subsurface are designed to represent terrains where recent fluvial-

like features suggest the presence of near-subsurface ground ice and probably liquid

water. We performed measurements on volcanic and sedimentary materials that may be

present on these sites under the appropriate geophysical conditions that may exist in those

terrains. We then simulated the backscattered radar echo arising from each site in the 2

MHz frequency band, using the Finite Difference Time Domain (FDTD) algorithm, in

order to evaluate the instrument performances to probe the subsurface stratigraphy of each

site. Our results confirm that the near-subsurface rich iron oxide mineralogy controls the

instrument performances in terms of penetration depth and signal-to-noise ratio in the 2

MHz frequency band. We finally discuss the geophysical and geoelectrical sounding

conditions that could lead to an ambiguous detection of shallow subsurface water on Mars

for the Netlander GPR.

INDEX TERMS: 3210 Mathematical Geophysics: Modeling; 1794 History of

Geophysics: Instruments and techniques; 5144 Physical Properties of Rocks: Wave attenuation; 5109 Physical

Properties of Rocks: Magnetic and electrical properties; KEYWORDS: Mars, hydrology, GPR, sounding,

simulation, FDTD

Citation: Heggy, E., P. Paillou, F. Costard, N. Mangold, G. Ruffie, F. Demontoux, G. Grandjean, and J. M. Malezieux, Local

geoelectrical models of the Martian subsurface for shallow groundwater detection using sounding radars, J. Geophys. Res., 108(E4),

8030, doi:10.1029/2002JE001871, 2003.

subsurface of Mars, at a depth of few hundreds meters.

1. Introduction

Water could flow out from an underground ice rich satu-

[2] Models of the thermal structure of the Martian crust

rated layer covered locally by volcanic altered materials

suggest that the thickness of frozen ground (the depth at

[Malin and Edgett, 2000a].

which the local temperature rises above the ice fusion point)

[3] Efficient sounding methods are required in order to

range from $2.5 5.0 km at the equator to $6 12 km at the

detect the water present in the Martian subsurface a hundred

poles [Clifford, 1993; Clifford and Parker, 2001]. Recently,

meters or a few kilometers deep. One of the best suited is

high-resolution images from the Mars Orbital Camera

based on sounding radars. Water, even if still present on

(MOC) on board the Mars Global Surveyor (MGS) orbiter

Mars at shallow depth (less then 300 m), will be difficult to

reveal the possible presence of water layers in the near

detect using drilling and seismographs. Radar sounding

methods, either from orbit or from surface based systems,

Observatoire Astronomique de Bordeaux, Floirac, France.

represent the adequate geophysical tool to inform us about

Also at Astronomy Department, Cairo University, Giza, Egypt.

subsurface water abundance and distribution, a parameter of

Universite Paris-Sud, Orsay, France.

primary importance to understand the history of the planet

Laboratoire de Physique des Interactions Ondes-Matiere-ENSCPB,

[Ori and Ogliani, 1996; Berthelier et al., 2000; Clifford et

Talence, France.

Bureau de Recherches Geologiques et Minieres, Orleans, France.

al., 2001].

Institut Environnement, Geo-Ingenierie, Imagerie et Developpement,

[4] Three radar instruments are planned in the current

Talence, France.

decade to probe the Martian subsurface and detect the

presence and distribution of subsurface water layers. In

2003, the Mars Advanced Radar for Subsurface and Iono-

0148-0227/03/2002JE001871$09.00

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GDS