###### Abstract  
With the rapid development of Earth system science, a new understanding of the complete Earth system has highlighted the crucial importance of integrated observations, especially in research involving large-scale geoscience phenomena. As an active sensor with all-time and all-weather capabilities, synthetic aperture radar (SAR) has been widely used in recent decades for Earth observation. However, the existing spaceborne, airborne, and ground-based SAR systems have difficulty providing temporally consistent and spatially continuous Earth observation data on a global scale. As Earth's only natural satellite, the Moon is a very promising Earth observation platform. By deploying a transmitter on the Moon and a receiver on the high-orbit satellite, a Moon-based/spaceborne bistatic synthetic aperture radar (MS-BiSAR) can be formed. In this paper, the MS-BiSAR geometric model of Earth observation was established using ephemeris and orbit propagators with reference system transformations, and three different MS-BiSAR configurations were used to calculate and analyze their geometric characteristics and Earth observation coverage. The results show that with the advantage of wide swaths, continuous observation capabilities, and large coverage, such an MS-BiSAR could significantly contribute to monitoring and understanding large-scale geoscience phenomena. Moon-based Earth observation; bistatic SAR; observation geometry 2023152151[[https://doi.org/10.3390/rs15082151](https://doi.org/10.3390/rs15082151)]([https://doi.org/10.3390/rs15082151](https://doi.org/10.3390/rs15082151)) 21 February 20231521 February 20231  
transmitter and an airborne or low-Earth-orbit satellite receiver that can reduce the demand for transmitting power and provide higher imaging resolution, making it more feasible in engineering [6; 7]. However, in the research on large-scale geoscience phenomena, Earth scientists prioritize high swath width more than the improvement of image resolution. As for GSO-BiSAR, the imaging swath width of this system is still limited by the altitude of the receiving platform. Moreover, the use of a GSO satellite transmitter is hampered by energy supply limitations that necessitate long idle periods for battery charging, resulting in a limited effective illumination time for regions of interest. All of these factors present difficulties for the continuous, large-scale monitoring of the Earth's surface. Therefore, we need a more effective Earth observation platform that can enable observations of larger-scale geoscience phenomena to deepen our understanding of the Earth system [8; 9]. As the only natural and long-term stable satellite of the Earth, the Moon has gained attention from scientists over the past few decades. Especially after the 21 st century, countries around the world, especially the United States and China, have successively launched lunar exploration programs [10; 11; 12; 13]. Due to its unique advantage of Earth observation, the Moon is considered a potentially ideal platform for Earth observation. Compared to satellites, aircraft, and ground-based platforms used for Earth observations, the Moon-based Earth observatory has distinct characteristics and offers an opportunity to enhance our overall Earth observation system. The Moon-based observation platform has the following advantages [8; 14; 15]: First, due to tide locking, one side of the Moon is always pointing toward the Earth, so continuous Earth observation from the Moon is possible. Second, with a higher orbit, the Moon-based observation platform can simultaneously observe the Earth at the hemispheric scale, making it more suitable for the continuous observation of large-scale geoscience phenomena. Third, unlike the limitations of spaceborne platforms, Moon-based platforms can provide sufficient energy supply and space to deploy active sensors with high transmit power and large antennas.