Radiometric Cross-Calibration of Hyperspectral Microsatellites Using Spectral Homogeneity Factor

On-orbit radiometric calibration is essential for the quantitative use of hyperspectral satellite and sensor monitoring, but its frequency is constrained by available calibration sites, especially for microsatellites with limited imaging capabilities. To reduce dependence on specific sites for on-orbit radiometric calibration, this article introduces a cross-calibration method that uses spectral homogeneity factor (SpecHF) to select targets in open fields. Initially, utilizing hyperspectral images from the advanced hyperspectral imager on board the Gaofen-5B satellite, we developed the SpecHF and selected calibration targets in the Ulanbuh Desert, Inner Mongolia, China. Then, the cross-calibration of the Compact Continuous Tunable LVF-based Hyperspectral Imager on board the microsatellite QMX-1 and the well-calibrated orbita hyperspectral sensor carried by the Zhuhai-1 satellite was performed on 10 September 2022. The intrinsic offsets between two sensors caused by spectral response functions (SRFs) mismatches were compensated using the spectral band adjustment factor, which accounts for the target's spectral profile and the SRF of both sensors. The comparison of the cross-calibrated top-of-atmosphere reflectance from Q1C with datasets from the radiometric calibration network revealed high consistency, with a root-mean-square error of 0.032. Additionally, a ground simultaneous validation conducted in Wuxi, China, on 31 December 2022, demonstrated the high accuracy and effective performance of the cross-calibration results in real-world settings, achieving an average MAE of 0.009. The results show that SpecHF-selected spectral homogeneous targets are well-suited for on-orbit radiometric cross-calibration. By overcoming site limitations, this method provides a viable solution for facilitating the flexibility of on-orbit calibration.