11 - 9
GDS
HEGGY ET AL.: MARTIAN GEOELECTRICAL MODELS
À60 dB attenuation range. Among the previous discussed
[34] The reader must keep in mind that there is no unique
models, terrains similar to the Hadriarca Patera site seem to
description of the Martian geoelectrical properties, thus any
be the most interesting sites for optimal subsurface water
sounding radar whether orbital or ground located cannot
detection using sounding radar techniques, for both landed
have a unique evaluation of performances, results will be
systems such as the GPR of the Netlander mission and
strongly depending on the investigation site.
[35] The validity of the geological models presented and
orbital ones such as the MARSIS instrument. We then
hence geoelectrical modeling and simulations is mainly
strongly recommend similar sites for radar shallow subsur-
related to our present-day knowledge of the Martian upper
face investigations.
crust mineralogy and stratigraphy. We expect data from the
[32] Further simulations at a 20 MHz frequency show
Gamma Ray Spectrometer (GRS) and the Thermal Emis-
similar capabilities for mapping the subsurface water pres-
sion Imaging System (THEMIS) onboard the Mars Odyssey
ence in such favorable sites, but one should consider here
mission and future chemical and mineralogical analysis of
possible additional losses due to volume scattering effect
the Martian soil to be performed by the 2003 Mars Explo-
caused by rocks and fractures distribution in the superficial
ration Rovers (MER) to provide the missing information
layers [Beaty et al., 2001; Heggy et al., 2002]. Criteria of
concerning the chemical and mineralogical composition of
radar detection of subsurface water in a similar context
the Martian surface. We should then be able to improve the
should not be limited to the depth at which it may be
modeling of a more realistic case of the Martian subsurface.
present. In particular, ejecta deposits terrains could be
Such work is crucial for preparing the interpretation of data
unfavorable cases for a 20 MHz orbital sounder, where
that will be produced by the future radar instruments.
the high dielectric constant of the first volcanic layers will
decrease the wavelength to a critical value, that might then
increase considerably the volume scattering effect, and
[36] Acknowledgments. The authors would like to thank J.P. Parneix
for measurement and simulations facilities, J.J. Berthelier and the Netlander
perhaps totally screen a shallow ice-water interface. Similar
team for useful discussions.
phenomena have been observed in sounding temperate
glaciers [Watts and England, 1976]. Thus we expect the
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