Cross Calibration of SDGSAT-1/TIS Thermal Infrared Bands With FY-4A/AGRI

Launched in November 2021, the sustainable development science satellite-1 carries the thermal infrared spectrometer (TIS) as a pivotal payload. Achieving precise radiometric calibration for geophysical parameter accuracy is crucial. Leveraging the frequent cross-calibration capability of the geostationary satellite FY-4A/advanced geostationary radiation imager (AGRI), this study addresses observational geometry challenges. The proposed radiance correction model for FY-4A/AGRI effectively reduces radiance discrepancies caused by differences in satellite zenith angles between TIS and AGRI. After integrating the corrected data into nadir-observed statistics, the long-term brightness temperature (BT) bias of TIS and AGRI was monitored. The results show that the daytime and nighttime BT bias exhibit similar trends, with the
B
2 band mainly showing negative bias. Overall, the BT bias for the
B
2 and
B
3 bands is within 1 K. The standard deviation of the BT bias for approximately 2250 sample points was calculated, revealing the values of 0.22 K and 0.40 K during the daytime, and 0.31 K and 0.57 K at night. The introduced model error remains below 0.31 K. Regarding the uncertainty of the BT bias introduced by spectral matching, when the spectral broadening is 1.15 times the wavelength interval, the uncertainty is less than 0.29 K for
B
2 and less than 0.38 K for
B
3. This work enhances our understanding of radiometric calibration challenges, providing insights into satellite-based geophysical parameter accuracy.