11 - 8

GDS

HEGGY ET AL.: MARTIAN GEOELECTRICAL MODELS

Figure 5. The 2 MHz radar echo simulations corresponding to the four geoelectrical models. Figures

present the normalized losses in decibel (plain line) and the backscattered electric field versus the wave

round trip time (dash line). The dotted lines indicate the location of each subsurface geological interface;

high-resolution structures in the normalized loss curves represent the signal modulation and simulation

noises. Top left: (2.1) shallow aquifer associated with local geothermalism. Top right: (2.2) outwash

plains. Bottom left: (2.3) ejecta deposits model. Bottom right: (2.4) layered deposits terrain. The linear Y

axis scale of the electric field plots has been reduced to visualize reflections from the third interface.

Arrows indicate the signal peak corresponding to the water-saturated layer.

[30] The third case corresponds to a geoelectrical model

subsurface-layered structure. Without a known first order

free of water and iron-rich materials, such as the layered

geoelectrical model it is difficult to distinguish the signal

deposit terrains. Although the radar response from the basalt

corresponding to water interface. While in the case corre-

basement could be misinterpreted as a water-rich layer as

sponding to the outwash plains the backscattered echo

the case of the outwash plains (compare the last peak in

shows a clear response of the subsurface water interface

Figure 5, top and bottom right) a lower attenuation than the

at a deeper location (310 m), but with a strong attenuation of

one observed in volcanic context (compare the attenuation

the first subsurface layers, leading to a poor signal-to-noise

slope in Figure 5, top and bottom right) could help detecting

ratio. The most favorable case is represented by the

past hydrological sedimentary deposits (carbonates).

Hadriarca Patera volcano site, for which volcanic materials

[31] In the simulation corresponding to the ejecta deposits

presenting a reasonable attenuation factor cover a water-rich

model where the water-saturated layer is 260 m deep, the

layer at a depth of 160 m. The radar signal associated with

radar echo gives strong evidence of the presence of the

the wet basalt can be clearly observed, and remains in the