The energy received through remote sensing sensors contains the amount of reflected s olar energy and emitted energy of objects in middle-wave infrared (MWIR,3~5 μm).Usually,the reflected solar energy is weak in MWIR spectrum.In some certain situations like sun glint area in sea surface,however,the energy is relatively significant and less sensitive to atmospheric effects.Meanwhile,f or the satellite sensor which equipped with onboard calibration system,its onboard radiation performance of MWIR(using blackbody calibration)is quite stable.Therefore,the MWIR reflectance in sea surface glint area can be considered as a reference for cross-calibration between the solar reflected bands.Based on this idea,this paper constructed an improved non-linear split window modelthat is suitable for VIIRS (visible infrared imaging radiometer) MWIR band and used this model to calculate the MWIR reflectance of sun glint area in southern Indian Ocean.This model made statistics,getting the relationship between the reflectance of VIIRS M12 and M13 bands at first,and then used the non-linear split window algorithm to calculate the actual sea surface reflectance.The uncertainty of the simulation model was 0.83%.On this basis,this paper calculated sea surface reflectance of selected sample regions based on the data of VIIRS M12 band (center wavelength: 3.697 μm) in sun glint areas.And then verified the reflectance accuracy by two methods,getting the two accuracies were about 0.239% and 0.23%,respectively.It proves that the calculation model in this paper can greatly improve the accuracy compared to the situation when the sea surface reflectance is between M12 and M13 which are assumed to be equal (accuracy of2.48% and 1.03%,respectively).It also indicated that the model is feasible and effective to calculate the reflectance in sea surface glint area with VIIRS M12 MWIR band,and the accuracy can meet the requirements of MWIR sea surface reflectance as a calibration reference among bands.%传感器入瞳处接收到的中红外波段(3~5 μm)能量包含反射的太阳能量与地物自身的发射能量.通常该波段反射的太阳能量很弱,但在海面太阳耀斑区等特定情况下,被中红外通道探测到的反射太阳能量是比较可观的,且其对大气影响的敏感性较低,同时,对于搭载有在轨定标系统的卫星传感器,使用黑体定标后的中红外波段的在轨辐射性能相当稳定的.因此,考虑将中红外波段的海面耀斑区反射率作为用于反射太阳波段交叉定标的基准.基于这个想法,构建了改进的、适用于VIIRS(visible infrared imaging radio meter)中红外波段的非线性劈窗模型来计算南印度洋海面耀斑区中红外反射率.首先统计得到VIIRS M12和M13波段海面反射率的限定关系,然后使用非线性劈窗算法模拟计算海面反射率,模拟模型的不确定度为0.83%.在此基础上使用VIIRS的M12波段(中心波长为3.697 μm)太阳耀斑区数据计算选取的样本区的海面反射率.然后使用两种方法对反射率精度进行验证,精度分别为0.29%和0.23%,假设M12和M13波段海面反射率相等的反射率计算结果精度分别为2.48%和1.03%.该计算模型大大提高了精度,说明该模型用于VIIRS M12中红外波段计算海洋耀斑区反射率是有效可行的,其精度能够满足中红外波段海面反射率作为波段间定标基准的需求.
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