FY-3C MERSI太阳反射波段的交叉定标

为了实现中分辨率光谱成像仪(Medium Resolution Spectral Imager,MERSI)太阳反射波段的星上绝对辐射定标,本文采用国际通用的6个北非沙漠目标即伪不变目标,以高质量的SeaWiFS数据为参考,对FY-3C MERSI数据进行交叉定标。首先利用高质量的SeaWiFS数据构建天顶双向反射分布函数模型;其次,构建两个传感器的参数化光谱匹配因子;最后,基于前两部分工作进行交叉定标。本文构建的天顶反射模型可以准确地表达伪不变目标的天顶反射率,波段预测误差基本都在3%之内;考虑观测几何条件和吸收气体含量的参数化光谱匹配因子可以有效地预测MERSI的天顶反射率;交叉定标结果的时间序列十分稳定且无明显趋势,与伪不变目标的天顶辐射信号长期稳定且规律性变化的特点相一致,与L1定标结果存在一个系统偏差。该方法充分考虑和解决了交叉定标研究中轨道漂移、观测几何条件和光谱响应差异带来的不确定性问题,能够对卫星辐射性能进行有效的在轨监测和订正。

Cross-calibration of FY-3C medium resolution spectral imager in reflective bands

To ensure absolute calibration of the solar band of the Medium Resolution Spectral Imager(MERSI),a cross-calibration algorithm utilizing Sea-Viewing Wide Field-of-View Sensor(SeaWiFS)instrument over six Pseudo-invariant Targets(PTs)is developed and used to calibrate FY-3C\MERSI data.The technique involves three key steps Capturing the actual Bi-directional Reflectance Distribution Function(BRDF)characteristics using the well-calibrated SeaWiFS radiance data;Parameterizing the Spectral Band Adjustment Factors(SBAF)between SeaWiFS and MERSI sensor;and Cross-calibrating each screened MERSI observation based on the above two modules.The employed BRDF model can accurately predictρTOA as observed by SeaWiFS with small biases(within approximately 3%for most cases).Furthermore,the fitted SBAF are nearly unbiased estimations of the simulated values.The time series of the cross-calibration result is very stable and exhibits no obvious trend,which is consistent with the characteristic of long-term stability and regular change of radiation signal of PTs.Hence,there is a systematic deviation from the calibration result of L1.This method fully considers and solves the uncertainty due to orbit drift,i.e.,the difference between observed geometric conditions and spectral response in cross-calibration,and can effectively monitor and correct the radiation performance of satellites in orbit.