Assessment and Correction of the On-Orbit Radiometric Calibration in FY-3D MERSI-2 Thermal Infrared Channels

Abstract

Accurate radiometric calibration is fundamental to quantitative remote sensing. In this article, a thermal infrared radiative transfer model is first established, and then, the on-orbit radiometric calibration of the thermal infrared channels 23 (8.55 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> ), 24 (10.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> ), and 25 (12.0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> ) of the advanced MEdium Resolution Spectral Imager (MERSI-2) on the Chinese Fengyun 3D (FY-3D) satellite is evaluated and corrected against the channels of the Advanced Himawari Imager (AHI) on Himawari 8 satellite using the double difference (DD) method. The results indicate that the on-orbit radiometric calibrations in FY-3D MERSI-2 channels 23, 24, and 25 are slightly biased and certain variations exist between January and July 2020. In January 2020, the on-orbit calibration of MERSI-2 channel 23 is statistically consistent with that of AHI channel 11, and the calibration bias (mean ±standard deviation at the mean) is 0.04 ±0.27 K, whereas they are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.11~\pm ~0.49$ </tex-math></inline-formula> K and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 0.30\,\,\pm \,\,0.50$ </tex-math></inline-formula> K in MERSI-2 channels 24 and 25, respectively. In July 2020, the on-orbit calibration of MERSI-2 channel 25 is very consistent with that of the AHI channels with a calibration bias of 0.06 ±0.31 K, while they are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 0.18\,\,\pm \,\,0.23$ </tex-math></inline-formula> K and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 0.27\,\,\pm \,\,0.30$ </tex-math></inline-formula> K in MERSI-2 channels 23 and 24, respectively. The radiometric calibration biases are finally corrected by the linear fits on the matching observations.