Research On Equivalent Simulation And Data Processing Methods Of Chang'E-4 Lunar Penetrating Radar 2B Channel

Lunar Penetrating Radar(LPR)is one of the most vital scientific payloads onboard the Yutu rover.The LPR system is designed for high resolution image of lunar subsurface structures and providing guidance on stratigraphic division.During the interpretation and analysis of radar signal,the geological condition can be reconstructed from the two-way travel time,phase and amplitude of the radar echo.The radar echo suffers interference caused by various clutter such as the multi-reflection generated by the metal components on the rover,direct coupling,and surface reflections.For the investigation on the characteristics of LPR signal,the numerical experiment on the high-frequency antenna module of LPR system is conduct.In this paper,a method for simplifying the simulation model based on the back-calculation of equivalent excitation is proposed.Via modifying the equivalent source of the simulation model,the same waveform as the echo signal received with the interference caused by the rover can be generated and achieve a tremendous decreasing of simulation time.For the high-precision image of radar profile and reconstructing the subsurface structures,the accurate velocity model was extracted and the migration was performed on the LPR data.For targets of sub-wavelength scale,hyperbola shaped signals are generated on the radar profile due to the diffraction of electromagnetic waves.The angle of the hyperbola asymptote is directly related to the velocity of the electromagnetic waves.In this paper,the Plane Wave Destruction(PWD)algorithm is adopted to separate the reflected wave field and the diffracted wave field from the radargrams.The hyperbolas at different positions are extracted from the diffracted wave field for the inversion of velocity.Finally,the Kirchhoff migration is performed to obtain the high-resolution image of LPR data from high frequency channel.The migration result reveals the stratigraphic division beneath the path of Yutu-2 rover.Four interfaces of geological stratification can be identified at the depth of 9 m,15 m,17 m and 24 m.The shallow area within 1.3 m refers to the uniform fine-grained regolith.There are some reflection signals distributed in the area from 1.3 m to 9 m which are considered to be the void or ejecta buried in the regolith.Numerous dense and disordered reflection signals are distributed in the area from 9 m to 17 m.This part of reflections are considered to be the ejecta deposits of Finsen or Von Kármán L craters.The reflection at 24 m is considered to be generated by the fractured bedrock because the interface of the layer has a continuous and relatively uniform thickness,and shields a large amount of radar wave energy.Thus few strong reflections can be observed on the radargram beneath the interface.