Exploring Dielectric Signature of Martian Mid-Latitude Ice Using Earth Analog Study

Radar detection of substantial presence of mid-latitude subsurface ice on Mars has been subject to a wide debate and uncertain observations. More often ice dielectric signature as induced from the inversion of the real part of the dielectric constant (e.g. ɛ = 3) can be confused with other silicate rich materials that have close values such loose dry sediments in general. To uniquely identify ice dielectric signature, one must use the imaginary part of the dielectric constant as measured from the radar dielectric attenuation after deconvolving the scattering losses. Unfortunately the latest remains poorly quantified at both MARSIS and SHARAD frequencies, which in term constrain the ability to accurately assess the imaginary part of the dielectric constant, needed for identifying the ice among other low losses material. To address this ambiguity, we conducted wide-band ground penetrating radar (GPR) and resistivity investigations in well-characterized permafrost in Fairbanks (Alaska, USA). The area shows several geomorphological and geophysical similarities to recently observed terrains in the mid- and high-latitudes of Mars. The radar sounding surveys have been performed over the frequency range of 10-1000 MHz using four wide-band antennas with central frequencies of 40, 270, 400 and 900 MHz. This approach allowed us to quantify the dielectric and scattering losses mechanisms in temperate permafrost as a function of the sounding frequencies over a wide frequency band. Our results suggest dielectric loss rates of 0.24 ± 0.02 dB/m at 20 MHz and 4.74 ± 0.47 dB/m at 400 MHz, whereas the corresponding loss rates attributed to scattering are 1.00 ± 0.33 dB/m and 5.01 ± 0.52 dB/m respectively. Scattering losses were found to represent an average of ∼70% of the total signal losses at 20 MHz in temperate permafrost. In the light of these findings, we revised the dielectric attenuation to obtain an accurate figure of the imaginary part of the dielectric constant and hence constrain the ambiguities associated to the amount and presence of subsurface ice suggested to be present at Martian mid-latitudes such as in Deuteronilus Mensae area or Amazonis Planitia based on the interpretation of SHARAD radar data by Plaut et al., (2009) and Campbell et al., (2008). When considering scattering losses, the imaginary part of the dielectric constant was found to range from 0.004 to 0.008 for Deuteronilus Mensae and 0.005 to 0.018 for Amazonis. Such values suggested that the two above mentioned structures have different compositions: the first being formed of ice-rich sediments while the second is more consistent with low-loss volcanic deposits. Further analysis will be presented at the conference.