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为解决FY-3C/MERSI反射波段非线性响应导致传统两点定标不适用问题,提出了在轨宽动态综合辐射定标方法。融合多种不依赖于地面同步测量的替代方案,利用各方案定标样本的多等级反射率特性,实现遥感器宽动态范围的辐射定标。每种方案的定标样本采用分段平均方法进行等权重融合,最终定标系数基于融合后样本通过加权拟合回归获得。非线性特征采用发射前室外定标实验分析的二次项系数进行修正,在轨计算定标斜率和截距。分析和验证结果表明:各替代方案样本分布具有很好一致性,融合样本相关性可达0.99;综合定标结果在反射率大于10%的中高端目标回归残差小于1%,高端定标结果与基于深对流云目标的交叉定标(DCC)检验样本的相对差异小于1.5%,敦煌同步观测实验检验结果表明中端精度优于3%;由于MERSI对低亮度辐射响应能力显著降低,发射前室外定标实验获得的非线性系数不能适用,定标结果在低目标反射率出现高估现象。该成果可应用于所有FY-3C/MERSI反射通道,明显降低两点法定标的不确定性以及非线性的影响。
In order to solve the problem that traditional FY-3C / MERSI non-linear response caused the non-linear response of two bands, this paper proposed a dynamic integrated radiation calibration method. Fusion of a variety of alternatives independent of ground-based measurements, the use of programs to calibrate the sample multi-level reflectance characteristics of the remote sensor to achieve a wide dynamic range of radiation calibration. The calibration samples for each protocol were segmented and averaged for equal weight fusion, and the final calibration coefficients were obtained by weighted regression fitting based on the fused samples. The non-linear features are corrected by the quadratic coefficient of the outdoor calibration experiment before launch, and the calibration slope and intercept are calculated on the orbit. The analysis and verification results show that the sample distribution of each alternative has a good consistency and the correlation of the fused samples is up to 0.99. The comprehensive calibration results are less than 1% in the high-end target regression with the reflectivity of more than 10% Compared with DCC test samples based on deep convection cloud targets, the relative difference is less than 1.5%. The results of Dunhuang synchronous observation experiments show that the mid-end accuracy is better than 3%. Because of the low MERSI response to low-brightness radiation, The non-linear coefficient obtained by outdoor calibration experiment can not be applied, and the calibration result is overestimated at low target reflectance. This result can be applied to all FY-3C / MERSI reflection channels, significantly reducing the uncertainty of the two-point calibration and the non-linear effects.