The accurate radiometric calibration is very important for remote sensing optical sensors. Numerous astronomical measurements and model analyses have shown that the Moon is extremely stable in reflectance properties and can serve as a great absolute reference source. Jilin-1 satellite has made long-period observations of the Moon over a wide range of phase angles. However, the spectra displayed fluctuations after radiometric calibration with the provided coefficients. This is inconsistent with the lunar reflectance spectra, which are smooth and generally no sharp absorption. In this study, we conducted radiometric calibration for PMS2 onboard Jilin-1 Guangpu02 (GP02) satellite using the Moon as the calibration source. The calibration results were validated based on different lunar geological terrain, i.e., maria and highlands. The lunar phase curve obtained through the application of the lunar calibration coefficients derived in this study show good agreement with the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and PLEIADES data. The results indicate that: (1) the spectra become much smoother after lunar calibration, consistent with the characteristics of lunar spectra; (2) the lunar calibration results demonstrate exceeding linearity, with average linear fit uncertainty of 0.69% and goodness-of-fit ( R ² ) of 0.9997 for the calibration coefficients; (3) the average relative difference between the phase curves of PMS2 and SeaWiFS is 3.6% and 4.66% with PLEIADES. The obtained results confirm the effectiveness of our lunar calibration method. Although this method was specifically applied to the PMS2, the lunar calibration method is expected to be applicable to other Earth-orbiting satellites.

The accurate quantitative application of remote sensing heavily relies on achieving high-precision radiometric calibration for satellite optic sensors. The Moon has virtually no atmosphere and is an extraordinarily stable diffuse reflector, providing a distinct advantage for the calibration of space-based instruments as a calibration source. In this study, we conducted lunar calibration experiments for images obtained by the panchromatic multispectral sensor (PMS) aboard the GaoFen-4 (GF-4) satellite. The calibration pixels between GF-4 and Moon Mineralogy Mapper (M3) aboard Chandrayaan-1 are fit to obtain calibration coefficients. The ${R} ^{2}$ of fitting line from Band 1–Band 5 of GF-4 are 0.98, 0.97, 0.96, 0.98, and 0.98 in linear part, and 0.99, 0.96, 0.98, 0.98, and 0.99 in the nonlinear part, respectively, indicating a high level of fitting accuracy. The uncertainties of the calibration results for Band 1–Band 5 were determined as 7.7%, 7.1%, 7.7%, 5.9%, and 6%. Four comparisons were used to validate the calibration results, including spectral characteristic, disk-integrated irradiance between ROLO model and GF-4, reflectance between Interference Imaging Spectrometer (IIM) aboard Chang’E-1 (CE-1) and GF-4 in similar geometry, and irradiance calculated by laboratory calibration coefficient, vicarious calibration coefficient, and our lunar calibration coefficient. The comparison of spectral characteristics demonstrated a consistent agreement with the mineral composition, affirming the precision of the lunar calibration. The relative error between the irradiance of GF-4 and the ROLO model was less than 5% at small phase angles (<30°) and approximately 15% at large phase angles. Similarly, the relative error between the reflectivity of GF-4 and IIM was below 5.5%, further validating the efficacy of lunar calibration. Additionally, the comparison of irradiance calculated with three different calibration coefficients indicate the applicability of lunar calibration in verifying the accuracy of other calibration results. Our lunar calibration approach benefits from the high-resolution lunar observation images of GF-4, allowing for absolute radiance calibration based on the Moon without the need for an onboard calibrator. With saving the need for human and financial resources, lunar calibration is particularly suitable for high-frequency and long-term calibrations. This study underscores the potential of lunar calibration for use in a broader context, including its suitability for other Earth-orbiting satellites in the field of remote sensing.

The PMS2 spectral imager onboard JiLin-1 (JL-1) satellite conducted extensive lunar observations, capturing images of the Moon across multiple spectral bands ranging from 415 to 1012 nm, spanning a wide range of lunar phases over an extended period. Photometric modeling plays a key role in deriving the physical and photometric properties of the lunar surface, with photometric calibration serving as a critical step in enhancing data quality for subsequent analyses. In this study, the PMS2 data are used for disk-integrated photometric modeling across these bands with the Hapke model. We analyze the wavelength dependence of photometric parameters and assess the effectiveness of photometric correction. Our study reveals a linear relationship between the amplitude of the opposition effect and wavelength, and gives the functional relationship between the other parameters and wavelength. Notably, we identified for the first time a peak in backscattering near 650 nm for the lunar surface. Additionally, we demonstrate that the model parameters derived from a disk-integrated approach provide accurate results when applied to disk-resolved photometric calibration.

Space-based observations of the total lunar eclipse on 21 January 2019 were conducted using the geostationary Earth-orbiting satellite Gaofen-4 (GF-4). This study represents a pioneering effort to address the observational gap in full-disk lunar eclipse photometry from space. With its high resolution and ability to capture the entire lunar disk, GF-4 enabled both quantitative and qualitative analyses of the variations in lunar brightness, as well as spectra and color changes, across two spatial dimensions, from the whole lunar disk to resolved regions. Our results indicate that before the totality phase of the lunar eclipse, the irradiance of the Moon diminishes to below approximately 0.19% of that of the uneclipsed Moon. Additionally, we observed an increase in lunar brightness at the initial entry into the penumbra. This phenomenon is attributed to the opposition effect, providing scientific evidence for this unexpected behavior. To investigate detailed spectral variations, specific calibration sites, including the Chang’E-3 landing site, MS-2 in Mare Serenitatis, and the Apollo 16 highlands, were analyzed. Notably, the red-to-blue ratio dropped below 1 near the umbra, contradicting the common perception that the Moon appears red during lunar eclipses. The red/blue ratio images reveal that as the Moon enters Earth’s umbra, it does not simply turn red; instead, a blue-banded ring appears at the boundary due to ozone absorption and the lunar surface composition. These findings significantly enhance our understanding of atmospheric effects on lunar eclipses and provide crucial reference information for the future modeling of lunar eclipse radiation, promoting the integration of remote sensing science with astronomy.