Scan-mirror emissivity calibration for imager’s two-mirror scanner with covariance matrix adaptation–evolution strategy

Himawari-8 and Himawari-9 are the newest Japanese geostationary meteorological satellites currently on orbit. The Advanced Himawari Imager (AHI) is the key payload of the mission. Calibration anomalies on orbit were identified with the infrared bands. The evaluation result of deep space infrared radiance clarified that the radiance includes the infrared radiance error depending on the scan-mirror angle. The error is known to be due to the angular dependency of the scan-mirror emissivity (SME). We propose a calibration method for each SME depending on the incident angle for a two-mirror scanner, which has two one-axis scan mirrors and a line sensor on one optical path. The proposed method uses the covariance matrix adaptation–evolution strategy. The proposed method was verified using Himawati-9 observation data. The proposed method reduced the infrared radiance error depending on the scan-mirrors angle by generating two new SME functions. The method uses on-orbit observation data and a radiometric model to generate the functions. Himawari-9/AHI images use the SME functions generated by the proposed method.