风云三号A星中分辨率光谱成像仪反射太阳波段辐射定标
Calibration for the Solar Reflective Bands of Medium Resolution Spectral Imager Onboard FY-3A
中文摘要：
中分辨率光谱成像仪（MERSI）是搭载在我国第二代极轨气象卫星风云三号（FY-3）上的一个主要仪器。总结了MERSI在仪器设计、定标算法、发射前及在轨性能以及仪器性能验证等方面的信息。针对MERISI可见光星上定标器(VOC)的跟踪监测发现，在过去两年，它的太阳反射波段（RSBs）发生了显著的衰减，特别是较短波长通道（<500nm）衰减量超过10%，最大衰减发生在第8波段，约20%。但波长较长通道的性能相对稳定，衰减量小于5%。两个短波红外通道电子增益出现随机跃动，导致发射后的定标系数存在频繁波动。以上结果与其他两种替代定标方法相比（即中国遥感卫星辐射校正场定标，简称场地定标和基于Terra/MODIS敦煌沙漠场景交叉定标），结论一致。MERSI针对大气顶辐射亮度或反射率定标的总不确定度小于5%。定标结果为FY-3A/MERSI定标系数的更新提供了重要的参考和评估。
中文关键词：
衰减率，仪器性能跟踪，中分辨率光谱成像仪，反射太阳波段定标，替代定标
KeyWords：
Degradation rate, instrument monitoring, Medium Resolution Spectral Imager (MERSI), solar reflective band calibration, vicarious calibration (VC)
Abstract：
The Medium Resolution Spectral Imager (MERSI) is a key instrument onboard Fengyun-3 (FY-3), the second generation of polar-orbiting meteorological satellites in China. This paper summarizes the knowledge of MERSI instrument in terms of sensor design, calibration algorithm, prelaunch and on-orbit characterization, and performance verification. The calibration monitoring of its reflective solar bands (RSBs) is primarily conducted using a visible onboard calibrator and found that it has a significant degradation on the order of 10% in its shorter RSB bands (< 500 nm), with the largest in band 8 of about 20% during the past two years. However, the performance at longer wavelength bands is relatively stable with a change of less than 5%. It is shown that the postlaunch calibration of the two short-wavelength infrared bands has frequent fluctuations because of random jumps in their electronic gains. These results are consistently verified by two kinds of vicarious calibration (VC) methods: China Radiometric Calibration Sites VC and intercalibration using Terra/ Moderate Resolution Imaging Spectroradiometer over Dunhuang desert. The overall uncertainty in the MERSI top-of-atmosphere radiance or reflectance is less than 5%. These results provide the important reference and evaluation for the update of the FY-3A/ MERSI calibration coefficients.