基于改进型反射率基法的资源三号卫星多光谱相机在轨辐射定标研究

针对资源三号卫星(ZY-3)多光谱影像特点，提出了一种改进型反射率基法，实现相机在轨辐射定标。该方法以ZY-3 Level 1A 级影像为数据源，建立严格的几何模型获取定标点处准确的观测几何参数，降低因影像重采样和成像几何产生的误差对辐射定标精度的影响。基于山东东营遥感综合实验，利用两点法和多点法获取ZY-3多光谱相机在轨辐射定标系数。与官方定标系数相比，多点法的定标精度高于两点法定标精度。通过分析各定标点与拟合直线间的离散程度后发现，水体定标点的残差较大，其中绿波段残差值约为67.39%。以置信度95.4%为标准，可将水体定标点判识为误差点。在剔除水体后，采用多点法获得的定标系数除近红外波段相对差异优于5%以外，其他波段相对差异均优于2%。该结果表明该改进型反射率基法能够获得精度可靠的绝对定标系数，可以为其他类似卫星在轨辐射定标提供参考依据。

In-Flight Radiometric Calibration for ZY-3 Satellite Multispectral Sensor by Modified Reflectance-Based Method

Through integrating multi-spectral sensor characteristics of ZY-3 satellite, a modified reflectance-based method is proposed and used to achieve ZY-3 satellite multispectral sensor in-flight radiometric calibration. This method chooses level 1A image as data source and establishes geometric model to get an accurate observation geometric parameters at calibration site according to the information provided in image auxiliary documentation, which can reduce the influences on the calibration accuracy from image resampling and observation geometry errors. We use two-point and multi-points methods to calculate the absolute radiometric calibration coefficients of ZY-3 satellite multispectral sensor based on the large campaign at Dongying city, Shan Dong province. Compared with ZY-3official calibration coefficients, multi-points method has higher accuracy than two-point method. Through analyzing the dispersion between each calibrationpoint and the fitting line, we find that the residual error of water calibration site is larger than others, which of green band is approximately 67.39%. Treating water calibration site as an error, we filter it out using 95.4% confidence level as standard and recalculate the calibration coefficients with multi-points method. The final calibration coefficients show that the relative differences of the first three bands are less than 2% and the last band is less than5%, which manifests that the proposed radiometric calibration method can obtain accurate and reliable calibration coefficients and is useful for other similarsatellites in future.