The 3–5 MHz global reflectivity map of Mars by MARSIS/Mars Express: Implications for the current inventory of subsurface H2O |
| |
| Authors: | J Mouginot A Pommerol W Kofman P Beck B Schmitt A Herique C Grima A Safaeinili JJ Plaut |
| |
| Institution: | aLaboratoire de Planétologie de Grenoble, UJF-Grenoble I/CNRS, 38041 Grenoble Cedex 9, France;bUniversity of California Irvine, Earth System Science, Irvine, California 92697, USA;cPhysikalisches Institut, Space Research & Planetary Sciences Division, Universität Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland;dJet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA |
| |
| Abstract: | We extracted the surface echo power from 2 years of MARSIS measurements. The retrieved values are calibrated to compensate for changes in the distance of the spacecraft to the surface and for the attenuation of the signal by the ionosphere. The results are used to build the first global map of surface echo power at 3–5 MHz. The surface echo power variations are primarily caused by kilometer-scale surface roughness. Then, we derive the values of dielectric constant of the shallow subsurface materials by normalizing the surface echo power map using a simulation of MARSIS signal from the MOLA topography. As a result, we obtain a map that characterizes the dielectric properties of the materials down to a few decameters below the surface. Dielectric properties vary with latitude, with high values in mid-latitudes belts (20–40°) and lower values at both equatorial and high latitudes. From the comparison of MARSIS reflectivity map to GRS observations, we conclude that the reflectivity decrease observed poleward of 50–60° corresponds to the onset of water-ice occurrence within the regolith. Assuming homogenous ground composition and texture at the scale of the MARSIS resolution cell, our inferred volume of ground water ice is of 106 km3, equivalent to a polar cap. Low reflectivity areas are also observed in equatorial regions. From radar studies alone, equatorial low dielectric constant values could have different interpretations but the correlation with GRS hydrogen distribution rather points toward a water-related explanation. |
| |
| Keywords: | Mars Surface Radar observations Data reduction techniques |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
