Methodological Research On Lunar Penetrating Radar And Interpretation Of Chang'e 3 Radar Data

The Lunar Penetrating Radar?LPR?carried by China's"Chang'e-3"?CE-3?and"Chang'e-4"?CE-4?mission is a method of insitu detection which is mounted on the rover.This kind of scientific payload detects lunar subsurface when the rover travels on the moon.LPR uses high-frequency electromagnetic waves?1MHz¹0GHz?to detect the lunar subsurface geological structure and regolith thickness with high resolution.According to the LPR data,the following scientific and engineering research objectives can be achieved:obtaining the thickness distribution of regolith along the path of the rover,and estimating the electromagnetic parameters of the lunar rocks and regolith which provide a basis for the estimation of lunar mineral resources;providing a better understanding of the relationship between lunar topographic features and geological structures;providing scientific basis for the study of lunar formation and evolution;providing the necessary information for the location of the future lunar base.This paper studies the modeling of the lunar regolith,electromagnetic response simulation,LPR data processing,parameter estimation,geological interpretation of the landing site and so on.The forward modeling of lunar nearsurface,radar response simulation and analysis were carried out to provide technical support for the detection mechanism understanding and the real data interpretation.The calculation,correction and preliminary processing of Chang'e-3 LPR data were developed for the analysis of reflected signals.High-precision estimation and inversion methods are designed for obtaining the physical parameters of lunar regolith and rocks which help to quantify potential exploitable lunar resources and analyze the resource distribution patterns.The geological interfaces under the landing site is explored for deepening the understanding of the formation and evolution of the subsurface layers and also supporting the further lunar and deep space exploration.?1?A comprehensive model of lunar regolith is established.Through applying fractal technology to the terrain modeling,we give the terrain of moon on a small scale accurately.Abrasive grain technology was introduced to simulate an irregular abnormal body.A stochastic modeling method is applied to describe the random medium.Besides,we also consider the permittivity change with depth.The comprehensive model deepens the understanding of the formation and evolution of lunar regolith.The electromagnetic response forward modeling of the established model was carried out according to the Finite Difference Time Domain.Compared with the simulation results of the simple model,the simulation results of the lunar regolith integrated model can reflect the parameters of the regolith more really.?2?The LPR data of Chang'e-3 mission is processed.We introduce the regional information of the landing site at first,and study the format of the data.Considering the complex environment on the lunar surface and the influence of the instrument,we processed the first channel?CH-1,60MHz?and the second channel?CH-2,500MHz?respectively.The processing processing methods include bandpass filtering,gain and other conventional methods.Finally,clear LPR images are obtained.?3?The structure and evolution of the regolith on the landing were studied.The contact interface of the regolith and the basement rock is explored according to forward simulation results.F-K?Frequency-wavenumber?filtering that highlights the contact surface of the regolith and the basement rock is carried out.The energy distribution of the LPR data helps to stratify the lunar regolith.Finally,by combining this with the history of the Moon,regional geology,and particularly the LPR data,we deduce the evolution of the regolith on the CE-3 landing site.?4?The electrical parameters and TiO₂+FeO content of lunar regolith are estimated.According to the geometric propagation law of electromagnetic waves,the propagation paths of two different electromagnetic waves are used to deduce the position of the anomalous body and the electrical parameters of the medium.The method is proved to feasible in theory.A simple model and a complex model of lunar regolith is simulated for the verification of the method.The estimated parameters are consistent with the models.The LPR data collected by CE-3 mission whose CH-2 data are with different offsets give us the chance to estimate the dielectric constant of regolith on the landing site.The results of the Apollo program show that the dielectric constant is intrinsically linked to the density and the iron-titanium content of regolith.Combined with the estimated dielectric constant from LPR data,the density and the TiO₂ and FeO content are obtained.?5?We propose anadaptive rock extraction method based on local similarity constrains to achieve the rock location and quantitative analysis for regolith.Firstly,a processing pipeline is designed to image the LPR CH-2 data.Secondly,we adopt f-x EMD based dip filter to extract low-wavenumber components in the two data.Then,we calculate the local similarity spectrum between the two set of the filtered CH-2 data.After a soft threshold function,we pick the local maximums in the spectrum as the location of each rock.Finally,according to the extracted result,on the one hand,the depth of regolith is obtained,and on the other hand,the distribution information of the rocks in regolith which change with the path and the depth is also revealed.?6?The shallow geological structure on the CE-3 landing site is analyzed.The first channel of the CE-3 data detected the shallow surface geological structure of Sinus Iridum area.o solve the limitation of noise.We adopt shearlet transform as a promising tool of data analysis and noise attenuation.The different distribution of noise and signal in shearlet domain decreases the difficulty of noise attenuation.To optimize the denosing strategy,we replace a local adaptive thresholding function with the conventional hard threshold.In the strategy,shearlet transform is a promising tools of data analysis and noise attenuation to highlight the useful events and improve the SNR of LPR CH-1 data.The improved quality of the processed data is helpful for geological stratification and interpretation.After obtaining the shallow and deep processed data,events have been tracked in the processed result,and 12 possible interfaces are obtained.The shallow geological structure analysis provides valuable information to understand the reflections of LPR data and offers a reference for future lunar missions.