Computation Of Microwave Radiation And Scattering From Lunar Surface And Subsurface Layer Detection

Since the sixties of last century, there have been all kinds of methods to detect the Moon, with the purpose of learning the formation and evolutive history of the Moon and other celestial bodies by investigating the information about terrain, internal structure and compositions of the Moon, and promoting the innovation and development of relative subjects. In lunar exploration, the microwave remote sensing is an important technology to reveal the global internal structure and compositions in surface layer of the Moon. Unlike the remote sensing to the Earth, it's difficult to directly prove results obtained from remote sensing data about the Moon, so the validity of the results relies on the understanding, processing and analyzing on the data. For this reason, the modeling of lunar regolith and analyzing are of great impartance, which is also an important in lunar exploration.Although the Moon is very far from the Earth, the microwave radiative theory and the electromagnetic scattering theory offer the powerful basis for studying the radiation and scattering from lunar regolith. Meanwhile, the development of computer and the appearance of high performance workstation offer the hardware condition for quantitative computation of radiative and scattering behaviors from the lunar surface. By numerical computation, it's efficient to analyze the radiative and scattering behaviors of different lunar regolith model, which will be helpful for designing detection system and proposing inversion methods. With comparisons of theory results and measurements, it will be helpful for explaining the lunar characteristics and learning the internal structure of the Moon. Thus, researches in this thesis will focus on the numerical computation of the radiative and scattering behaviors from lunar surface, including:Firstly, the thesis introduces the basic theory for microwave radiative measurement and electromagnetic computation. Based on the summary of lunar regolith such as lunar surface roughness, temperature profile of lunar regolith and lunar regolith models, multilayered lunar model with rough surface is proposed according to the requirement of detecting lunar internal structure and ice water, which offers the basis for studying the radiative and scattering behaviors from lunar surface. Meanwhile, to reduce the complexity in numerical methods, the difference between one-dimensional (1D) surface and two-dimensional (2D) surface is analyzed with Gaussian rough surface. Results show that 1D surface is efficient to simulate 2D surface with the same roughness on two dimensions, which is useful to reduce the complexity in numerical methods.Secondly, the radiative brightness temperature and scattering behavior form lunar surface are computed, based on multilayered lunar model. For the radiative brightness temperature, a hybrid method combining the microwave radiative transfer theory and the Method of Moments (MoM) is proposed and validated. Results show that the roughness of lunar surface will affect the brightness temperature and the effect is related to the polarization and observation angle of the radiometer. By adjusting the observation angle, the effect by the roughness can be reduced at vertical polarization, which is beneficial to retrieve lunar parameters. For the scattering behavior, the coherence between echoes from lunar surface and subsurface is studied, and the subsurface detection by stepped frequency radar is proposed. With the computations by the MoM, the detection performance is discussed, which shows that the stepped frequency signal can offer more scattering behavior and the method is efficient for the case of very rough lunar surface with enough contrast between permittivities of two media. With numerical results, the effect of potential ice water is also given. The existence of ice water will cause the raise in emissivity and brightness temperature. However, a single means is not efficient to estimate the existence and content of ice water. The compounding detection is needed with more remote sensing equipments and the joint inversion for lunar parameters is possible.Thirdly, the Generalized Banded Matrix Iterative Approach (GBMIA) is proposed to compute the scattering behavior from large-scale lunar model with stratified rough surfaces. The accuracy of the GBMIA is checked with the MoM. Results show that the GBMIA can reduce both the memory requirement and computation time, and introduce little error, which is suitable for analyzing the scattering behavior from lunar surface.Finally, the enhancement method for the spatial resolution of remote sensing system is studied. By signal processing technique, it's equivalent to narrow the width of the antenna beam, which can reduce the scale of computation model in numerical method. Simulation and experimental results show that the improved high frequency raised method can obtain better spatial resolution and the inversion is more accuracy.