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Titel |
WISDOM GPR performance assessment in a cold artificial environment |
VerfasserIn |
M. Dechambre, V. Ciarletti, M. Biancheri-Astier, A. Saintenoy, F. Costard, R. Hassen-Khodja |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250065515
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Zusammenfassung |
The WISDOM (Water Ice Subsurface Deposit Observation on Mars) GPR is one of the
instruments that have been selected as part of the Pasteur payload of ESA’s 2018 ExoMars
Rover mission. WISDOM has been designed to obtain information about the nature of the
subsurface along the rover path with the objective to explore the first ~ 3 m of the soil with a
vertical resolution of a few centimetres. The sub-surface properties that can be addressed
with WISDOM are variations in composition, texture, stratification (e.g., number,
thickness and orientation of layers), the presence of unconformities and other structural
characteristics (such as fractures and the deformation of strata). It is then essential
to quantify the performances of WISDOM in controlled conditions, and several
full polarimetric measurements have been carried out with the prototype in a cold
artificial environment. The main objectives are the detection of different interface
between homogeneous materials with WISDOM. The characterization of the material
(porosity, % of water, dielectric properties, thickness and depth, temperature -¦) is
well-controlled. The cold room facility of IDES at Orsay (France) has been used, the
ambient temperature ranged from -7Ë C to -10Ë C. A tank laying on the metallic floor
(height: 0.5m, width: 0.80 m, length: 1.20m) in macrolon can contain liquid or frozen
water or layers (dielectric contrasts) of home-maid permafrost (frozen saturated
sand) with and without embedded objects or fractures. The temperature inside the
medium (ice or permafrost) is controlled, the radar antennas are put on a sheet of
polystyrene over the tank. Frequent measurements were performed (every 2cm) along
a track from one side to the other side of the tank. The experimental conditions
were:
(1)dry cold sand (Fontainebleau sand) : porosity 35% density 2,67 (2) saturated wet sand :
35% of water (3) permafrost (frozen saturated sand) : 35% of ice content
1 layer: 3 consecutive experiments : 10cm dry sand ( 1) 10cm saturated sand (2) 10cm
permafrost(3)
2 layers :previous 10cm permafrost in the bottom +3 consecutive experiments : 10cm dry
sand ( 1) 10cm saturated sand (2) 10cm permafrost(3) . Basalt rocks and air fractures are or
are not embedded in the layers
Values of the permittivity of dry sand and permafrost were retrieve by two different
ways.
1.Retrieval of the sand and permafrost permittivity from delay measurements knowing the
layer thickness d
Ér = ct-2d = n2
2. Retrieval of the sand and permafrost permittivity from amplitude measurements knowing a
calibration reference (reflection over a metallic plate), R is the Fresnel coefficient between the
air and the medium.
Aint/ = R = n– 1-,É = 1+-R-= n2
Aair n +1 r 1- R
Results :
Internal layering is observed. The transition between dry sand and permafrost
can be detected.
The permittivity can be retrieved from delay or amplitude measurements as well
from delay measurements : dry sand Ér = 2.71 permafrost Ér = 3.72
from amplitude measurements : dry sand Ér = 2.73 permafrost Ér = 3.35
Embedded objects are detected,
Fracture and its orientation is detected. |
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