sounding the ganymede’s crust with a gpr
DESCRIPTION
Sounding the Ganymede’s crust with a GPR. V. Ciarletti 1 , A. Le Gall 1 , M. Biancheri -Astrier 2 , J-J. Berthelier 1 , S.M. Clifford 3 , D. Plettemeier 4 , M. Hamelin 1 1 LATMOS, Guyancourt, France 2 IDES, Orsay, France 3 LPI, Houston, TX, USA 4 TUD, Dresden , Germany . - PowerPoint PPT PresentationTRANSCRIPT
Sounding the Ganymede’s crust with a GPR
V. Ciarletti1, A. Le Gall1, M. Biancheri-Astrier2, J-J. Berthelier1, S.M. Clifford3, D. Plettemeier4 , M. Hamelin1
1LATMOS, Guyancourt, France2IDES, Orsay, France
3LPI, Houston, TX, USA 4TUD, Dresden, Germany
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Scientific Objectives
• Characterize the 3D compositional (ice purity) and physical (porosity, structure) properties of the Ganymede Landing Site down to a depth of ~100m to a few km
• Identify potential shallow (<1 m depth) and deep (up to ~1+ km) structures
• Clues to understand the large-scale geologic evolution of the Landing Site
• Characterize the electromagnetic environment and potential activity of the thin atmosphere (ambient Jovian HF background noise, potential atmospheric discharges )
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Overview
A stationary, impulse, multiband HF GPR operated from the surface
• designed to conduct geologic investigations of planetary environments in both the near and deep subsurface (~1m – few km)
An enhanced version of the low-frequency GPRs developed for
• The original Mars NetLander (CNES) • The original ExoMars mission (mono and bi-static
operations)
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
The instrument main features
Frequency bands • 2-4 MHz deep soundings (from 100 m to a few kms with a resolution of ~50m)
3D mapping• 3 components of the magnetic field + 2 for the electrical field • Retrieval of the direction of arrival of the echoes - 3D mapping of the reflecting
structures
Modes of operation• Active• Antenna impedance measurement• Passive
Detection of weak echoes• Deployment on the surface• Coherent additions up to 228 (in monostatic operation) to improve the SNR
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Mono-static configuration (NetLander)
Magnetic sensor
Electrical antennas
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Mono & Bi-static configuration (former ExoMars mission)
Magnetic sensor
Electrical antennas
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Coherent additions efficiency
0 1 2 3 4 5 6 7 8 9 10
-10
0
10
nbcoh=1
0 1 2 3 4 5 6 7 8 9 10
-10
0
10
nbcoh=8nbcoh=64
0 1 2 3 4 5 6 7 8 9 10
-10
0
10
nbcoh=64nbcoh=4096
Tens
ion
mes
urée
(mV
)
0 1 2 3 4 5 6 7 8 9 10
-10
0
10
nbcoh=512
0 1 2 3 4 5 6 7 8 9 10
-10
0
10
nbcoh=4096
Retard (s)
nbcoh=4194304
nbcoh=65536
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
• Electrical antennas deployed on the surface (transmission and reception)• 2 perpendicular dipoles (2 X 35 m long resistively loaded ribbon
monopoles)
The antennas system
Electrical antennas deployment system
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Magnetic antennas (reception)• 10 cm long search coil magnetic antenna
The antennas system
Magnetic sensor
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Demonstration of 3D investigation
Mono-Static Investigations of the Subsurface in Antarctic
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Demonstration of 3D investigation
Mono-Static Investigations of the Subsurface in Antarctic
Topography reconstruction
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Application to Ganymede
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
In active mode: Assessing the stratigraphy of a grooved terrain, a crater or a putative cryo-volcanic features on Ganymede will significantly help to determine and describe the geological processes that have shaped the moon’s surface and bring new constraints on its age.
Application to Ganymede
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
In active mode: could contribute greatly to the understanding of the relationship between this subsurface ocean and the surface by revealing compositional boundaries between different ice sheets.
Application to Ganymede
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
In the antenna impedance measurement mode: will help to characterize Ganymede’s crust composition and in particular the proportion of non-ice components in the near surface.
εr=3 σ=10 -5S/m
Simulation
εr~3 σ~10-5 S/m
MeasurementSimulation
Electrical HF antenna impedance measurement
Application to Ganymede
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Passive mode: will monitor Jupiter radiation and its variations with time.
Better to operate on the anti-Jupiter side of Ganymede!
Summary
The data acquired by such low-frequency GPR will provide local information about the geology of the Landing site:
• at a scale (~100 m – a few kms) and resolution (~10 – 100 m) • including its composition, stratigraphy and structure.
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Back up slides
Mono-Static HF measurementsPassive measurements Impedance measurements
Magnetic sensor Electrical antenna
Bi-Static HF measurements
Mono & Bi-static configuration (former ExoMars mission)
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”
Demonstration of 3D investigation
Bi-Static Investigations of the Subsurface
1st interface
2nd interface
3rd interface
TxIn profile:
International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”