FY-3B中分辨率光谱成像仪(MERSI)不能实现可见光近红外波段的星上绝对定标。为了提高MERSI高信噪比窄波段通道的辐射定标精度,针对国际通用的6个北非沙漠目标,利用高质量的SeaWiFS数据构建天顶双向反射分布函数(BRDF)模型,借助MODTRAN辐射传输模型和ERA-Interim再分析资料吸收气体数据构建光谱匹配因子,对FY-3B MERSI 5年的在轨运行数据进行交叉定标研究。所构建的天顶反射模型可以准确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一致。与MERSI L1业务化定标结果相比,第8~12波段的定标结果偏低,相对偏差小于0,而第13~16波段的定标结果偏高,相对偏差大于0。除了波段8以外的其他8个波段的偏差基本都在-5%~5%以内。波长小于600 nm的波段的月平均偏差较大,特别是三个蓝光波段(第8~10波段);第13~16波段的月平均偏差相对稳定,基本都在-5%~5%以内。

FY-3B medium resolution imaging spectrometer (MERIS) cannot achieve the absolute calibration for the visible and near-infrared bands. To improve the MERIS absolute calibration accuracy, the six widely used north African desert pseudo-invariant targets are adopted herein, taking the advantage of the high-quality SeaWiFS data to construct the bidirectional reflectance distribution function(BRDF) model and then using the MODTRAN radiative transfer model and ERA-Interim absorption gas reanalysis data to construct the spectral band adjustment factor (SBAF). Lastly, five years of FY-3B MERIS data are used for the cross-calibration. The constructed BRDF model in this study can accurately express the top of atmosphere (TOA) reflectance (ρ^TOA) over the pseudo-invariant targets, and the prediction error is basically within 3%. The TOA reflectance of MERIS can be effectively predicted through the parameterized SBAF which considers the observation geometry and absorbed gas content. Cross-calibration results show that the time series are extremely stable and have no obvious trends, which are consistent with the characters of TOA reflectance over pseudo-invariant targets. Compared with the operational calibration results of MERIS L1, the cross-calibration results of bands 8--12 are lower and the bias is less than zero, whereas for bands 13--16, the results are higher and the bias is greater than zero. Except for band 8, the biases of the other eight bands are within -5%--5%. The monthly mean deviation of bands with a wavelength less than 600 nm are larger, particularly the three blue bands (bands 8--10). The monthly mean relative deviations of bands 13--16 are relatively stable, and they are basically within -5%--5%.