The Study Of Geometric Characteristics Of Moon-based Earth Observation

At the beginning of the 21 st century,Moon-based Earth observation is becoming a frontier for lunar research and Earth observation.However,the moon-based platform for Earth observation,the Moon,has unique geometric characteristics and is very different from the airborne and spaceborne platforms.It brings both opportunities and challenges to the implementation of Earth observation,specifically:(1)It has a relatively stable orbit and always faces one side of the earth;(2)Its own scale is much larger than the airborne and spaceborne platforms,so it is necessary to consider the observation differences brought about by different locations on the lunar surface;(3)It has a unique libration and will affect its attitude;(4)The relevant geometric parameters of the moon-based earth observations will continuously change with the movements of the Sun,Earth and Moon,and this change rule is different from the spaceborne and airborne platforms which needs special analysis.(5)The distance between the earth and the moon is long and it will produce a second-order aberration,which needs to be considered when constructing a strict imaging geometry model.However,there is still a lack of research on the geometry of moon-based earth observations.Therefore,it is necessary to establish a scientific framework for the study of moon-to-earth observation geometries and to carry out meticulous and in-depth analysis to deepen understanding of their geometric characteristics and changing laws.Therefore,this paper focuses on the optical geometric characteristics of moon-based earth observations,and specifically carries out the following work:(1)Geometry Modeling of Moon-based Earth ObservationTaking the DE430 ephemeris data and Earth Orientation Parameters as the experimental data of this paper,a comprehensive conversion framework of the lunar based earth observation related reference systems that takes into account the lunar libration is established.Simplified moon-based earth observation geometry model is constructed and it lays the foundation for the qualitative and quantitative analysis of the geometric characteristics of the moon-based earth observations.Besides,the nadir point algorithm is designed and statistically analyzed the changing rule on the year and interannual scale.(2)Analysis of Coverage Characteristics of Moon-based Earth ObservationAn index,effective coverage,for evaluating the coverage of moon-based earth observations is proposed.An algorithm for the parameters related to the optical coverage of moon-based earth observations is designed.The variation of observation period,observation frequency and effective coverage is analyzed.Moreover,we compare the differences in the effective coverage caused by different positions and angle errors on the lunar surface.The moon-based earth observation shows good observation ability both locally and globally.It can achieve high-frequency observations in low-latitude regions and can realize long-term continuous observations in high-latitude regions.From the perspective of ground observation,the positive center of the moon is more suitable as a moon base.(3)Analysis of Angular Characteristics of Moon-based Earth ObservationAn algorithm for the optical angular parameters of the moon-based earth observations was designed.The variation of the zenith,elevation and azimuth angles of the solar angles and the observation angles at a single time and over a long period of time was analyzed.The performance of solar angles were compared and discussed.In general,the moon-based earth observation has a combination of observation angles and have the ability to observe variable angles on the surface of the earth.Although limited to the observation time,the moon-based earth observation can still fully reflect the characteristics of the solar angle of the observation target.This has great potential for research on macroscopic scientific phenomena of the earth such as radiation transmission and energy balance.(4)Study on the geometric modelling of the moon-based earth observationA rigorous geometric imaging model considering the effect of light travel differences of the moon-based earth observation was established,and the image of the moon-based earth observation was simulated.The verification of the photograph of the earth photographed by the Chang-3 geomorphology camera was performed and it shows that the model has good accuracy.At the same time,the direction of the line of sight is discussed on the surface of the moon,which lays a solid foundation for the subsequent quantitative analysis modeling and observation simulation of the macroscopic scientific phenomena of the lunar observatory.In this paper,we systematically analyzed the nadir points,coverage characteristics,angular characteristics,and imaging geometric models of moon-based earth observations,and established a systematic framework and method for the study of moon-based earth observation geometry.It shows that the moon-based earth observation has suitable observation period,relatively stable and good coverage ability,and abundant angle information,it also lays a solid theoretical and methodological basis for subsequent research on the moon-based earth observations facing the macroscopic scientific phenomena of the earth.