FY-3B MERSI短波红外波段温度响应与在轨定标分析

风云三号B星(FY-3B)中分辨率光谱成像仪(Medium resolution spectral imager, MERSI)的两个短波红外波段(1.64和2.13 $\mu$m) 采用光伏碲铬汞探测器,由于辐冷问题导致短波红外波段探测器的实际工作温度远高于设计值,影响了其在轨辐射特性。 对处于高温工作状态的FY-3B MERSI短波红外波段的长时间序列在轨辐射特性进行了较为系统的研究分析。采用冷空观测和 遥测温度时间序列数据开展了工作温度对遥感器响应的影响分析,发现短波红外波段的冷空值与探测器温度之间存在正 相关关系。采用线性模型描述仪器响应的温度依赖性,获得了温度校正因子；温度每变化1度, 1.64和2.13 $\mu$m波段冷空观 测值分别变化约0.7\%和5\%。进行温度校正后,冷空观测时间序列的波动显著降低。采用全球多目标定标方法获得了 短波红外波段的在轨辐射响应变化,在参考温度下,2011年11月至2016年12月,1.64和2.13 $\mu$m波段的总衰减分别 约为6\%和11\%。通过与Aqua中分辨率成像光谱仪(Moderate-resolution imaging spectroradiometer, MODIS)的 多年交叉比对分析,发现不管是否在定标过程中进行温度校正,采用基于长时间序列趋势建模的日定标更新后MERSI 与MODIS的辐射偏差较为稳定,可以满足7\%的定标指标要求。

Temperature Sensitivity and on-Orbit Calibration Analysis for FY-3B MERSI Shortwave Infrared Bands

The two shortwave infrared (SWIR) bands (1.64 and 2.13 $\mu$m) of Medium Resolution Spectral Imager (MERSI) onboard FY-3B are detected by photovoltaic HgCdTe detectors. Due to the issue of radiant cooler, the SWIR band detectors operated at higher temperatures than specification, which influenced its on-orbit radiometric response. The long-term on-orbit radiometric properties of FY-3B MERSI SWIR bands at high working temperature were systematically studied. The time series of space view observation and telemetry temperature measurement were used to analyze the on-orbit temperature dependency. It revealed that there were positive correlations between the SWIR band space view and the detector temperature. Linear models were used to describe the temperature dependency and the temperature correction factors were derived. When the detector temperature changed 1℃, the space view digital number varied 0.7\% and 5\% for bands of 1.64 and 2.13 $\mu$m, respectively. After the temperature correction, the long-term variation of space view observations decreased significantly. The multi-site calibration method was used to obtain the on-orbit sensor radiometric response change. At the reference temperature, the total attenuations of 1.64 and 2.13 $\mu$m bands were about 6\% and 11\% respectively from Nov. 2011 to Dec. 2016. Through the cross comparison against Aqua moderate-resolution imaging spectroradiometer (MODIS), it revealed that when the daily calibration update model based on long-term trending analysis was applied, the radiometric differences between MERSI and MODIS were relatively stable for many years, regardless of whether the temperature effect was accounted for or not in the calibration process, which can meet the calibration expectation of 7\%.