Lunar Dielectric Constant Inversion From Mini-RF Data And Its Application

Since the1960s, a large amount of data on rock and soil parameters distributionare obtained from moon exploration plan represented by the United States and theformer Soviet, which makes human have a deeper understanding to the lunar terrain,composition, structure, and so on. The lunar surface is covered with a thick layer ofsoil, whose size is about40-100μm, and there are also some rocks with several metersin diameter buried in the soil. The average lunar soil thickness is commonly4to5m,which is rich in the important strategic resources, like ilmenite. The detection of lunarsoil electrical parameters has an important significance for the exploration,development and utilization of lunar resources.Formerly, the dielectric constant inversion on the lunar surface used opticalreflectivity data observed by the Clementine and Lunar Prospector satellite tocalculate the content of FeO and TiO2, then estimate soil dielectric constant byempirical formula between FeO and TiO2determined by regression analysis to Apollosamples. Due to the limited quantity of Apollo samples we collected, the experienceformula determined by these samples may not be able to realize an accuratecalculation for dielectric constant of the whole lunar surface. In this paper, a directdielectric constant inversion using the Mini-RF dual polarization radar data ispresented, and combined with special radar echo data of the Mini-RF products toidentify spatial distribution characteristics of the crater ejecta and volcanic pyroclasticrock.In consideration of similar rough rolling characteristics between lunar and earthsurface, this paper has a detail illustration on the applicating condition of radar’sscattering model with rough surface quantitatively described by the ground radarremote sensing, including Kirchhoff, GOM, POM, SPM, IEM, Oh Model, Duboismodel, Campbell model and Shi model, and make the comparison and analysis. Campbell model, which has applied to the moon and the inversion result of thedielectric constant is close to the measured values on moon landing points, and Ohexperience model, which experience parameters are less and application range is wide,are used as the dielectric constant inversion models of lunar surface.In order to verify the applicability of Campbell model and Oh model on lunarsurface, the horizontal polarization and vertical polarization scattering coefficients arerespectively calculated according to stokes parameters provided by the Mini-RF dataproducts, and dielectric constants on Luna16landing area are respectively calculatedby Campbell model and Oh model combining the roughness parameters provided byLOLA. Then the comparison is made with the measured dielectric constants. Theconclusion is that the dielectric constant inverted by Oh model is very close to and themeasured value, and the relative error and the root mean square error are small, whilethe difference between the results inverted by Campbell model and the measuredvalue is large. As a result, Oh model is selected as the model to invert the dielectricconstant of lunar surface.The selected method is used to invert the dielectric constants of crater ejecta andvolcanic pyroclastic rock distribution. At the same time, the circular polarization ratio,the polarization degree and relative phase are calculated based on stokes parameters.The polarization degree and relative phase are used to make them decomposition, which is to get the distribution characteristics of physical scatteringmechanism in the study area. On optical images, crater ejecta are commonly brightcolors, volcanic pyroclastic rocks are dark, and some region boundaries are not clear.While, on radar images, due to the different geological units of lunar surface show thedifferent microwave scattering characteristics, a comprehensive analysis is needed forthe study area using the distribution of circular polarization ratio and scatteringphysical mechanism and the dielectric constant, and then a qualitative analysis ismade according to the influence by the radar wave penetration ability to the spatialdistribution of crater ejecta and volcanic pyroclastic rocks.