Earth's radiation budget is a core process of the Earth-atmosphere system, closely linked to global climate and environmental changes. While current satellite observations have greatly advanced our understanding of Earth's radiation budget, low-Earth orbit and geostationary satellites struggle to achieve both temporal continuity and spatial consistency. Accurately capturing the laws of Earth’s outgoing radiation is key to studying this budget.

Recently, a new study published in Journal of Geophysical Research: Atmospheres confirmed that lunar observations offer a unique perspective to solve this problem. The research team consists of scientists from the Institute of Atmospheric Physics (IAP) at the Chinese Academy of Sciences (CAS), Aerospace Information Research Institute/CAS, and University of Chinese Academy of Sciences.

"Traditional observations mostly focus on regional or local radiation characteristics," Dr. Ye Hanlin from IAP/CAS, first author of the study, explained. "From the Moon, Earth appears as a complete disk, allowing us to extract planet-scale dominant signals while suppressing small-scale weather noise."

The team found that changes in Earth's emitted radiation observed from the Moon-based platform are mainly dominated by first-order and second-order spherical harmonic functions, accounting for about 90% of the variation rules.

Diagram comparing ultra-long-range, low-Earth orbit, and geostationary satellite observation systems (Image by Ye Hanlin)

This acts like a "noise reduction" process for Earth’s emitted radiation, filtering out interference from local weather events and clearly capturing planet-scale radiation features. These spherical harmonic functions are just like the unique "fingerprints" of Earth's emitted radiation.

The study also clarified the periodic patterns of radiation changes: synodic month periodicity (related to the Moon’s phases relative to Earth) is dominated by sectorial harmonic components; sidereal month and its half-period come from zonal harmonic components, driven by the periodic latitudinal shift of the observation point caused by the Moon’s orbit; intraday periodicity reflects dynamic changes in the field of view due to Earth’s rotation.

"A Moon-based platform provides a new, long-lasting holistic view of Earth, which is highly unique," said Professor Guo Huadong, corresponding author of the study from the Aerospace Information Research Institute, Chinese Academy of Sciences.

The study confirms that holistic Earth observations can provide important support for accurately estimating Earth's outgoing radiation and advancing global climate change observation study.

Paper info:

Ye, H., Guo, H., Liang, D., et al. (2025). Spherical harmonic fingerprints characterize Moon-based disk-integrated Earth's emitted radiation signatures. Journal of Geophysical Research: Atmospheres, 130, e2025JD044758. https://doi.org/10.1029/2025JD044758