Helium-3(3He) implanted by solar wind in the lunar regolith is a valuable resource because of its potential as a fusion fuel.On the basis of the Apollo regolith samples,a linear relationship between 3He abundance and solar wind flux,optical maturity and TiO2 content has been presented.China successfully launched its first lunar exploration satellite Chang-E 1(CE-1) on October 24,2007.A multi-channeled microwave radiometer was aboard the satellite with the purpose of measuring microwave thermal emission from the lunar surface layer.From the multi-channel brightness temperature(Tb) observed by CE-1,the global distribution of the regolith thickness was inverted from the multi-channel Tb,and was used to evaluate the total amount of 3He per unit area in the lunar regolith.The global inventory of 3He was estimated as being 6.6×108 kg;3.7×108 kg for the lunar nearside and 2.9×108 kg for the lunar farside.
In China's first lunar exploration project,Chang-E 1,the multi-channel (3.0,7.8,19.35,37 GHz) microwave radiometers were aboard the satellite,with the purpose of measuring microwave brightness temperature from lunar surface and surveying the global distribution of lunar regolith layer thickness,and global evaluation of 3He content.To analyze the modeling of microwave radiative transfer from three-layered media of lunar surface,some factors,such as the cratered lunar surface roughness,scattering of regolith particulate medium with temperature profile,are discussed.Based on the statistics of the lunar cratered terrain and using Monte Carlo (MC) method,the cratered lunar surfaces are numerically generated.The triangulated network is utilized to divide the undulated lunar surface into discrete triangle meshes with the size 10 m as a digital surface topography.The reflectivities of each plane mesh are calculated,and the average reflectivity for all MC-realized lunar surfaces is obtained.It is found that under the spatial resolution of 30 km×30 km of Chang-E 1 radiometer observation,the lunar surface can be well modeled as a flat surface.It makes the predominance of the parameters,such as the regolith layer thickness and stratified structures,to be studied.Using the radiative transfer equation of stratified media with dense scatterers,the scattering coefficient of the regolith particulate medium is found negligible,and the emission is mainly governed by the absorptive property of the medium.Brightness temperature of multi-layered media,i.e.lunar soil,regolith layer with temperature profile and underlying rock media,are derived and calculated,and relevant main factors to affect the modeling and emission simulation are analyzed.
