Calibration Method of High Spectral Infrared Atmospheric Sounder Onboard FY-3D Satellite

Abstract

High spectral infrared sounders possess distinct advantages that were exhibited in application of atmospheric temperature and humidity profiles retrieval, numerical weather prediction (NWP), climate change study and trace gas measurement due to high spectral resolution, low radiometric noise and high spectral and radiometric accuracy. A high spectral infrared atmospheric sounder (HIRAS) that was designed and manufactured completely by China will be carried onboard FY-3D and it is a sign of new age of infrared high spectral vertical sounding system in China. HIRAS is a Fourier interferometer and high radiometric precision is required for better application of data and also because radiometric noise and calibration errors are magnified in the inversion process to derive atmospheric parameters. Noise equivalent-temperature errors and calibration precision of the order of 0.1 °C and absolute errors of less than 0.3 °C are required to obtain temperature profile with rms errors of less than 1 °C. To develop calibration algorithm software and validate instrument data, complex calibration method is applied which using Cold Screen of 17 K and Internal Calibration Target of 313 K as calibration reference source and based on engineering model instrument vacuum calibration experiment data. Preliminary calibration results revealed that a strong absorbing peak at 800 cm⁻¹ and need deep investigation. For FOV1, 2 and 4 the bias are less than 1 K for wide spectral range and are about 1–2 K just in location of less than 700 cm⁻¹. FOV3 reflects bias of 2–4 K in whole LWIR band and need more data to verify it. Future work will be focused on non-linearity and spectral correction and the radiometric bias can be expected reach less than 0.7 K.