Using the Moon for On-Orbit Absolute Radiometric Calibration of GaoFen-4 PMS

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.