We know very well the Moon’s appearance in the visible wavelengths. What the Moon in the midinfrared (MIR) looks like is still a mystery. We present detailed appearance of the MIR Moon observed by a high‐resolution geostationary satellite and reveal the essence behind its appearance. The appearance of the MIR Moon is opposite to its normal visible appearance and shows limb darkening. Both the absolute and the relative brightness distribution of the MIR lunar disk changes with the solar incidence angle i. The signatures of the MIR Moon are controlled by both the reflection and the emission of the lunar surface. The center‐to‐limb temperature variation across the lunar disk is clearly shown. The slower decrease of the brightness temperature when moving away from the subsolar point than the Lambertian model represents topographic effects.

The diurnal variation and distribution of lunar surficial hydration (OH/H₂O) is of great significance for understanding the solar wind implantation and water cycle on the Moon. Lunar south pole is an ideal place to study the diurnal variation of surficial hydration due to the large number of repeat observations of the same region, which is very limited in mid‐ or low‐latitudes. Here we showed clear 0.5‐hr interval diurnal variation of surficial hydration at lunar south pole. The variation of hydration band depth with local time is exactly the opposite to the variation of temperature, indicating that lunar surficial hydration changes sufficiently with temperature. This relationship indicates that both the diurnal variation and hydration content are latitude dependent. Our observations support the hypothesis that the diurnal variation of hydration on the Moon is due to the formation of metastable hydroxyl.

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.

Lunar surface temperature variations provide key information about the thermophysical properties of the regolith. To date, temperatures have been measured using telescopes and orbiter instruments, providing information from mid‐infrared to long infrared (IR) wavelengths. Here, we report on temperature measurements in the short‐wavelength IR at centimeter scales observed in situ by the Chang’E‐4 rover. These local observations are an important complement to the existing large‐scale data. We show that even at 2.39 µm, where reflected radiation dominates the spectrum, thermal information can be retrieved from the data. The observed thermal radiances and derived temperatures depend on the observation geometry, specifically the relative azimuth angle between Sun and detector. This indicates that surface roughness on subresolution (millimeter) scales causes a non‐Lambertian radiation pattern of the emitted flux that is per definition independent of the observation angle. This behavior must be considered when deriving temperatures and thermal properties of lunar regolith.

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.