Inversion Of The Lunar Surface Rock Abundance From Measurements By Satellite-based Microwave And Infrared Radiometers

With the development of science and technology,explorations for the universe have gradually extended to a new stage.As a satellite of the earth,the moon can provide important reference value for the explorations of other planets.So far many countries have launched their own lunar explorations,and a large amount of measurements for understanding and analyzing the moon are obtained by the ground-based telescope observation,satellite,or direct landing.From the thermal observations,a large number of thermal anomalies are found.In previous studies,it was found that lunar surface rock is an important parameter to explain for these anomalies.Due to the difference of the physical and chemical properties between lunar rocks and regolith,the thermal characteristics of lunar surface will be obviously affected by rocks.Therefore,the analysis of rock abundance plays an important role in the study of lunar thermal characteristics and the analysis of lunar resources.In order to calculate the lunar surface rock abundance,first we need to establish a onedimensional heat conduction model of the whole lunar surface,and obtain a look-up table for the local temperature of the moon both with time and depth.The one-dimensional heat conduction equation is a partial differential equation in two dimensions including both time and depth,with two boundary conditions.In the upper boundary condition,we need to consider the local terrain,latitude,and also the albedo to adapt to the actual situation.In order to reflect the influence of terrain on the heat conduction process,we need to calculate the horizontal and the vertical slope respectively in situ according to the digital elevation data,and then conduct the solar incidence angle from the observed local time,combined with the horizontal slope and the vertical slope calculated above.By solving the one-dimensional thermal equation,a look-up table of the temperatures varing with time and depth for the whole day is obtained.In order to obtain the look-up table of rock temperature,the research results of bandfield et.al are adopted,which is derived based on the physical and chemical properties of foam basalt(a common rock on the moon).Then We extract the 37 GHz channel data of the microwave radiometer onborad Chang'E-2.Combined with the diurnalphysical temperature profile of lunar regolith with topography,the simulations of microwave radiative brightness temperature for both lunar regolith and the rocks are conducted on the basis of microwave radiative-transfer theory.By adapting the different ratio of lunar regolith and rocks to match the measured microwave radiative brightness temperature,the rock abundance map for the whole lunar surface can be obtained.Then we extract the measurements of some regional areas to validate inversion results of the rock abundance.Tycho,Crookes,and Nishina craters are chosen to show their simulated and measured microwave radiative brightness temperatures,and a good agreement could be figured out.The next,we use the channel 8 infrared data from Diviner onboard LRO to evaluate the lunar surface rock abundance.The temperatures of regolith and rocks are respectively solved from the real-time one dimensional thermal model and then the thermal radiation are transferred to radiations through the Plank formula.Then,based on the measurements at corresponding local time and location,the rock abundance for the whole lunar surface can be determined by analyzing proportional contributions from regolith and rocks.The rock abundance results will be averaged if duplicate results obtained at the same location.At last,we select the measured infrared observations at Giordano Bruno,Harpalus,Tycho,Aliacensis craters.,comparing with the simulation temperatures with rocks.It is found that the measurements and simulations can be well matched based on our method.