Large-scale geoscience phenomena are increasingly attracting more attention because of their great scientific and social significance. However, many existing earth observation systems lack the ability to conduct long-term continuous observations at a regional-to-global scale because of spatial and temporal coverage limitations and systematic bias. In this work, we propose a new platform, the moon, and discuss its potential and optical geometrical characteristics for observing large-scale geoscience phenomena. Based on the Jet Propulsion Laboratory ephemerides, the reference systems transformation and a simulation system of moon-based earth observations were developed. Numerous experiments were carried out and a series of simulation images are presented, which illustrate the wide swath and continuous observation characteristics of such a lunar observatory. In order to quantify the performance of moon-based earth observations, a simplified geometrical model was constructed and data were analyzed. The sublunar points were found to be unique parameters with the ability to characterize the relative positions between moon and earth. We also defined an effective coverage parameter for assessing the optical coverage ability of moon-based earth observations. The calculation showed that the average value of the introduced coverage parameter from 1960 to 2050 was 0.500, and the coverage remained stable in different years. Furthermore, the total daily visible time and repeated times of different positions on the earth surface are analyzed and the effect of different positions on the lunar surface of the observatory are evaluated. The result shows that such a moon-based approach could make significant contributions to the monitoring and understanding of large-scale geoscience phenomena.

As a new concept platform for Earth observation, a Moon-based platform has the advantages of large-scale, constant and long-term dynamic Earth observations that can meet the needs of conducting systematic research on the Earth. However, a Moon-based platform has particular differences from space-borne and air-borne platforms because of its long distance from the Earth and the vast expanses of the Moon. In this article, we present three contributions. First, we propose a formula to describe the relative position of the Moon-based platform and Earth observation target. Second, we establish an observation geometry model and discuss three key observation parameters that are vital to the observation scope and coverage calculation. Third, a new observation scope and coverage analysis method is established in order to demonstrate that a suitable Moon-based Earth observation platform site can be located in the full observation region. We establish a geometric model for a Moon-based platform based on the Earth orientation parameters and Jet Propulsion Laboratory (JPL) ephemerides. Then, three key parameters including the visibility of the Earth from the Moon, nadir point, and Earth viewing angle are calculated using the proposed model. These parameters determine the observation scope and coverage of the Earth. The Earth-facing hemisphere of the Moon is divided into four regions, including the full observation region and the incomplete observation regions. Compared with the selenocentric case, during orbital periods, the maximum nadir point’s latitudinal and longitudinal difference in terms of placing sensors on the Moon surface is about 0.3°, the maximum viewing angle difference of the Earth is about 0.005°, and the maximum angular difference of the Moon-based platform and the Sun is about 0.24°. Thus, the maximum coverage difference is about 0.1%, so that placing sensors on the full observation region would result in better Earth observation performance.

As the earth's only natural satellite, the Moon has unique advantages as an earth observation platform because of its long observation distance and the vast expanse of the lunar surface. To observe the earth from the Moon, the looking vector direction and its variation regularity need to be investigated. In this paper, we first establish a Moon-based earth location algorithm to reveal the variations of the looking vector. In this algorithm, assuming the sensor points to the earth, the looking vector expressed as azimuth and elevation angles is calculated, and the intersection point between the looking vector and the earth's ellipsoid is solved using the relevant equations. The mathematical expression of the observational scope is also derived so as to determine the looking vector range if the looking vector direction is limited in the earth disk. Based on this algorithm, we describe the earth's motion in the lunar topocentric coordinate system and analyze the looking vector direction characteristics by assuming different positions on the lunar surface. In addition, the earth location error is evaluated by adding the looking vector errors. The results show that sensors at different positions on the lunar surface have different looking vector pointing characteristics and different earth location errors. The earth location error is relatively small in the high-latitude region of the Moon. Combining the restriction of lunar local topography, we suggest that the regions that latitude between 30 °N and 80 °N or 30 °S and 80 °S are the ideal locations for the Moon-based earth observation platform.

Although the precision of the surface parameters calculated from satellite data gets higher and higher, it is still difficult to guarantee the temporal consistency and spatial continuity for large scale geoscience phenomena. Developing new earth observation platforms is a feasible way to improve the consistency and the continuity. As the only natural satellite of the Earth, the Moon has special advantages as a platform for earth observation. This paper mainly discusses the advantages and the potential applications of moon-based earth observation, as well as the train of thoughts of further researches.

Moon-based platform is a potential platform that can realize the observations of large-scale geoscience phenomenon. Unlike existing earth observation platforms, the moon-based platform is equipped on a natural celestial body. Its position is calculated by the lunar position and libration derived from the planetary ephemeris. However, limited to the astrometric model and accuracy of observational data, no planetary ephemeris can provide absolutely accurate data, and this will lead to a platform's position error. This letter investigates the impacts of the platform's position error on geolocation for a moon-based sensor. We first made comparisons to the lunar position and libration derived from different planetary ephemerides so as to evaluate the magnitude of the platform's position error. Then, the Monte Carlo method was applied to simulate the platform's position error. According to the geometric model, the effects of the platform's position error on geolocation were presented. The results showed the effects of lunar libration error are associated with position on the lunar surface, while the differences of lunar position error effects are not evidently shown in different positions on the lunar surface. Furthermore, high-latitude regions of the moon are demonstrated to have less impact on the platform's position error, which would be suitable for equipping earth observation sensors.