Data preprocessing and preliminary results of the Moon-based Ultraviolet Telescope on the CE-3 lander

The Moon-based Ultraviolet Telescope （MUVT） is one of the payloads on the Chang＇e-3 （CE-3） lunar lander. Because of the advantages of having no at- mospheric disturbances and the slow rotation of the Moon, we can make long-term continuous observations of a series of important celestial objects in the near ultra- violet band （245-340 nm）, and perform a sky survey of selected areas, which can- not be completed on Earth. We can find characteristic changes in celestial brightness with time by analyzing image data from the MUVT, and deduce the radiation mech- anism and physical properties of these celestial objects after comparing with a phys- ical model. In order to explain the scientific purposes of MUVT, this article analyzes the preprocessing of MUVT image data and makes a preliminary evaluation of data quality. The results demonstrate that the methods used for data collection and prepro- cessing are effective, and the Level 2A and 2B image data satisfy the requirements of follow-up scientific researches.

Moon-based Earth observation:scientific concept and potential applications

Although Earth’s surface parameters obtained from satellite data have become more and more precise,it is still difficult to guarantee temporal consistency and spatial continuity for large-scale geoscience phenomena.Developing new Earth observation platforms is a feasible way to improve the consistency and continuity of such data.As the planet’s only natural satellite,the Moon has special advantages as a platform for observing Earth,including long lifetime,whole disk view,tectonic stability and unique perspective.After presenting the observation geometry constructed by using the ephemeris,this paper mainly discusses the characteristics of a lunar platform and the proper Moon-based sensors,as well as the scientific objectives of Moon-based Earth observation.Solid Earth dynamics,the energy budget of Earth,Earth’s environmental elements and the Earth-space environment are four potential applications analysed in this paper.

Exploring the influence of various factors on microwave radiation image simulation for Moon-based Earth observation

Earth observation technologies are important for obtaining geospatial information on the Earth’s surface and are used widely in many disciplines,such as resource surveying,environmental monitoring,and evolutionary studies.However,it is a challenge for existing Earth observation platforms to acquire this type of data rapidly on a global scale due to limitations in orbital altitude and field of view;thus development of an advanced platform for Earth observation is desirable.As a natural satellite of the Earth,placement of various sensors on the Moon could possibly facilitate comprehensive,continuous,and longterm observations of the Earth.This is a relatively new concept and the study is still at the preliminary stage with no actual Moon-based Earth observation data available at this time.To understand the characteristics of Moon-based microwave radiation,several physical factors that potentially influence microwave radiation imaging,e.g.,time zone correction,relative movement of the Earth-Moon,atmospheric radiative transfer,and the effect of the ionosphere,were examined.Based on comprehensive analysis of these factors,the Moon-based microwave brightness temperature images were simulated using spaceborne temperature data.The results show that time zone correction ensures that the simulation images may be obtained at Coordinated Universal Time(UTC)and that the relative movement of the Earth-Moon affects the positions of the nadir and Moon-based imaging.The effect of the atmosphere on Moon-based observation is dependent on various parameters,such as atmospheric pressure,temperature,humidity,water vapor,carbon dioxide,oxygen,the viewing zenith angle and microwave frequency.These factors have an effect on atmospheric transmittance and propagation of upward and downward radiation.When microwaves propagate through the ionosphere,the attenuation is related to frequency and viewing zenith angle.Based on initial studies,the simulation results suggest Moon-based microwave radiation imaging is realistic and viable.

Simulation of Moon-based Earth observation optical image processing methods for global change study

Global change affected by multiple factors,the consequences of which continue to be far-reaching,has the characteristics of large spatial scale and long-time scale.The demand for Earth observation technology has been increasing for large-scale simultaneoiis observations and stable global observation over the long-term.A Moon-based observation platform,which uses sensors on the nearside lunar surface,is considered a reasonable solution.However,owing to a lack of appropriate processing methods for optical sensor data,global change study using this platform is not sufficient.This paper proposes two optical sensor imaging processing methods for the Moon-based platform:area imaging processing method(AIPM)and global imaging processing method(GIPM),primarily considering global change characteristics,optical sensor performance,and motion law of the Moon-based platform.First,the study proposes a simulation theory which includes the construction of a Moon-Sun elevation angle model and a global image mosaicking method.Then,coverage images of both image processing methods are simulated,and their features are quantitatively analyzed.Finally,potential applications are discussed.Results show that AEPM,whose coverage is mainly affected by lunar revolution,is approximately between 0%and 50%with a period of 29.5 days,which can help the study of large-scale instant change phenomena.GIPM,whose coverage is affected by Earth revolution,is conducive to the study of long term global-scale phenomena because of its sustained stable observation from 67°N-67°S on the Earth.AIPM and GIPM have great advantages in Earth observation of tripolar regions.The existence of top of the atmosphere(TOA)albedo balance line is verified from the GIPM perspective.These two imaging methods play a significant role in linking observations acquired from the Moon-based platform to Earth large-scale geoscience phenomena,and thus lay a foundation for using this platform to capture global environmental changes and new discoveries.

The angular characteristics of Moon-based Earth observations

The Moon,Earth’s only natural satellite,is a potential new platform for Earth observation.Moreover,with the wide applicability of the angular information from remote sensing data,it has been attracting increasingly more attention.Accordingly,this study focuses on the angular characteristics of Moon-based Earth observations.Using ephemeris DE430 and Earth orientation parameters,the position and attitude of the Sun,Earth,and Moon were obtained and their coordinates normalized to a single framework using coordinate transformations between the related reference systems.Then,an angular geometric model of Moon-based Earth observations was constructed,and the corresponding angular algorithms were presented.The results revealed the angular range and distribution characteristics of Moon-based Earth observations.For every point on the surface of the Earth,the view and solar zenith angles all vary widely,which decreases with increasing latitude.The view and solar zenith angles all vary widely with the largest range of values in the equatorial and polar regions and a smaller range of values in mid-latitudes.Furthermore,the range of solar angles of Moon-based Earth observations is the same as that of alltime solar angles,indicating the potential for monitoring and understanding large-scale geoscientific phenomena using Moon-based Earth observations.

Progress of Earth Observation in China

China is expanding and sharing its capacity for Earth observation by developing sensors,platforms,and launch capabilities in tandem with growing lunar and deep space exploration.China is considering the Moon as a viable Earth observation platform to provide high-quality,planetary-scale data.The platform would produce consistent spatiotemporal data because of its long operational life and the geological stability of the Moon.China is also quickly improving its capabilities in processing and transforming Earth observation data into useful and practical information.Programs such as the Big Earth Data Science Engineering Program(CASEarth)provide opportunities to integrate data and develop“Big Earth Data”platforms to add value to data through analysis and integration.Such programs can offer products and services independently and in collaboration with international partners for data-driven decision support and policy development.With the rapid digital transformation of societies,and consequently increasing demand for big data and associated products,Digital Earth and the Digital Belt and Road Program(DBAR)allow Chinese experts to collaborate with international partners to integrate valuable Earth observation data in regional and global sustainable development.

The influence of lunar surface position on irradiance of moonbased earth radiation observation

As a platform for longer-term continuous moon-based earth radiation observation(MERO)which includes reflected solar short-wave(SW)radiation and long-wave infrared(LW)radiation,the huge lunar surface space can provide multiple location choices.It is important to analyze the influence of lunar surface position on irradiance which is the aim of the present work based on a radiation heat transfer model.To compare the differences caused by positions,the site of 0°E 0°N was selected as the reference site and a good agreement of the calculation results was verified by the comparison with the NISTAR’s actual detected data.By analyzing the spatial characteristics of the irradiance,the results showed that the irradiance on the lunar surface was of circular distribution and the instrument that was placed in the region of 65°W-65°E and 65°S-65°N could detect the irradiance most effectively.The relative deviation between the reference site and the marginal area(region of>65°S or 65°N or>65°W or 65°E)was less than 0.9 mW∙m^(-2) and the small regional differences make a small-scale network conducive to radiometric calibration between instruments.To achieve accurate measurement of the irradiance,the sensitivity design goal of the MERO instrument should be better than 1 mW∙m^(-2) in a future actual design.Because the lunar polar region is the priority region for future exploration,the irradiance at the poles has also been analyzed.The results show that the irradiance changes periodically and exhibits complementary characteristics of time.The variation range of irradiance for short-wave radiation is greater than longwave radiation and the irradiance of SW reaches the maximum at different times.The MERO at the polar region will provide valuable practical experiment for the followup study of the moon-based earth observation in low latitudes.