FY-3E 同平台成像仪对 HIRAS-II 定位与定标精度评估

The Infrared Hyperspectral Atmospheric Sounder II (HIRAS-II) is mounted on China's Fengyun-3E satellite (FY-3E), a meteorological satellite in dawn-dusk orbit. The high geolocation accuracy and radiometric calibration accuracy of the instrument are the keys to the quantitative application of its observational data. The relative deviations of geolocation and radiometric calibration of HIRAS-II are evaluated via cross-comparison by the Moderate Resolution Spectral Imager-Low Light (MERSI-LL) mounted on the same satellite platform. After the observational data samples of the two instruments are spatially matched, the MERSI-LL data is used to evaluate the observation background uniformity of the matched samples. The geolocation accuracy of HIRAS-II is evaluated with non-uniform background observation samples of sea-land or cloud boundary, and its radiometric calibration accuracy is evaluated with homogeneous background observation samples of clear-sky ocean and other scenes. Before cross-comparison, the hyperspectral simulated observational data of each infrared channel in MERSI-LL is obtained by integrating the HIRAS-II observed radiation spectrum with the spectral response function of each infrared channel in MERSI-LL. The results show that the geolocation of HIRAS-II at nadir deviates by 3. 53 km in the along-orbit direction and 2. 01 km in the cross-orbit direction. In terms of radiometric calibration accuracy, the mean radiation brightness temperature (BT) deviations of most channels in HIRAS-II and MERSI-LL are lower than 0. 50 K, and the standard deviation of the deviations is lower than 0. 40 K. Only the deviation of the 4. 05 μm channel is large to the low-temperature target, and the temperature dependence of this channel is obvious. The BT deviation of the 4. 05 μm channel fluctuates while that of the 8. 55 μm channel does not change significantly with the scanning angle. The variations in the BT deviations of the other channels with the scanning angle are related to the target temperature. The long time series analysis of the BT deviation shows that it remains stable as a whole.