CBERS-02 WFI的辐射交叉定标及其对植被指数的作用

本文以MODIS作为参考传感器，对CBERS-02星上的WFI传感器进行辐射交叉定标，得到WFI两个波段TOA辐亮度、表观反射率的增益与计数值偏移量，两个波段的计数值偏移量分别为42和21个DN左右。利用定标结果计算图像上另一均匀区的表观反射率。与MODIS反演的表观反射率比较验证。WFI与MODIS第1波段的表观反射率相差3．6％，第2波段相差-3．6％。检验结果说明，本文得到辐射交叉定标系数的精度能满足定量化应用的要求。为了说明辐射定标对植被指数的影响，本文选择5个实验区，比较分析了实验区图像辐射定标前后的NDVI。当WFI的DN值扣除定标得到的数字计数值偏移量后，DN值的NDVI与表观反射率的二次非线性拟合度可达99％。另外。WFI辐射定标前后的NDVI、RVI与MODIS反演的NDVI、RVI的比较分析说明，WFI辐射定标后表观反射率值的植被指数与MODI反演植被指数较接近，而且两个传感器RVI的差异小于NDVI的差异。

Radiometric Cross-calibration of CBERS-02 WFI with MODIS and the Effect on VI

With the MODIS as a reference sensor,the radiometric cross-calibration was performed for(CBERS-02) WFI and the calibration coefficients and the offsets were obtained.The offsets for both channels were very large,about 42 and 21 respectively.For validation,the calibration results were applied to another region of WFI image to get the apparent reflectance,which was compared to the one from MODIS image.The differences for both two corresponding channels were 3.6% and-3.6%,which demonstrated that the calibration results we got should satisfy the quantitative application.Five experimental regions from WFI images were selected to calculate their vegetation index both before and after radiometric calibration and the comparison showed that the degree of fitting using the quadratic polynomial function could reach 99% after the offsets were subtracted from the original DNs.The comparison between the NDVI and RVI from WFI and those derived from MODIS illustrated clearly that the VI derived from the WFI with calibration coefficients were much closer to those of MODIS and the variation of the RVI between two sensors was smaller than that of the NDVI.