On-Orbit Degradation Tracking of FY-3D/MERSI-II Based on Ocean Glint

The medium resolution spectral imager (MERSI-II) is an important sensor mounted on China’s second-generation polar-orbiting meteorological satellite Fengyun-3 (FY-3). However, due to the influence of its own or external conditions during the operation of the sensor, the detection performance of the sensor will be degraded. Based on the sun glint over ocean (ocean glint), this article conducted a four-year (2018–2021) long-term series tracking of the on-orbit attenuation performance of a total of 13 channels of FY-3D/MERSI-II from visible light to mid-infrared (400–2500 nm). With the 865 nm channel as the reference channel, through screening the effective pixels, the ratio of the reflectance of the channel to be tracked and the reference channel to be used as the tracking value for this research, and the on-orbit degradation of FY-3D/MERSI-II after launch was analyzed. The results show that the degradation of the channel with wavelength less than 500 nm is obvious, especially the 412 nm band has the largest attenuation rate, with an annual attenuation rate of 7.2%, and the annual degradation rate of 443 and 490 nm also exceeds 3.5%; meanwhile, their degradation also has a large oscillation characteristic. Most red and near-infrared bands (600–900 nm) and long-wave bands (>2000 nm) are relatively stable, with an annual degradation rate of no more than 2%. The research results can provide a reference for updating the subsequent calibration coefficients of FY-3D/MERSI-II.