Assessment and Correction of FY-3D/HIRAS Spectral Calibration Error Caused by Silica Gel Gas Contamination

The Hyperspectral Infrared Atmospheric Sounder (HIRAS) carried on the FengYun(FY)-3D satellite is a Fourier transform infrared spectrometer, which can improve the vertical detection capability of the atmosphere. The radiometric calibration accuracy of HIRAS depends on accurate spectral calibration. During the operation of the satellite, the spectral calibration accuracy of HIRAS will change continuously due to the mirror misalignment and the volatile silica gel gas appearing in the path of the interferometer optical system. Here the long-term absolute accuracy of the HIRAS spectral calibration is assessed by a forward radiative transfer model through a cross-correlation method. Subsequently, A two-step method is developed to determine the final configurations of the four detectors on each of the three HIRAS focal planes. The off-axis apodization correction is then performed using the dynamically updated off-axis parameters for all the detectors, achieving a spectral calibration accuracy superior to 2 ppm.