敦煌辐射校正场反射辐射偏振特性研究

卫星遥感器辐射校正场的地表反射辐射测量(例如地表反射率、地表辐亮度等)对卫星遥感器的在轨定标至关重要。由于地物光谱仪自身具有一定的偏振敏感性, 场地反射辐射的偏振特性将会引入偏振测量误差。采用基于偏振成像仪和塔吊的非定点测量方式以及基于偏振光谱仪和BRDF测量架的定点测量方式, 测量了敦煌场490 nm和670 nm波段场地反射辐射的多角度偏振分布和局地偏振均匀性。试验结果表明, 敦煌辐射校正场的反射辐射具有一定的偏振特性。偏振特性和波段有关, 490 nm波段偏振度明显大于670 nm波段。490 nm和670 nm波段的多角度偏振分布关于太阳主平面对称。在太阳主平面内, 前向散射区偏振度大于后向散射区, 并随天顶角变大而变大。两种测量方式获得了一致的偏振特性分布规律。获得了直径100 m区域的场地反射辐射局部均匀性, 均匀性在6%左右。研究场地反射辐射的偏振特性对于场地辐射探测方案的改进以及辐射测量精度的提高具有重要意义。

Research on polarization characteristics of reflected radiation on Dunhuang radiometric calibration site

Reflected radiation measurement(such as surface reflectance, surface radiance, etc.)from the radiometric calibration site is very important for the vicarious calibration of satellite sensors. Measurement error can be caused by the polarization effect of the reflected radiation from the radiometric calibration site, because of the fact that field instruments possess a certain degree of polarization sensitivity. A non-fixed-point measurement method based on multi-band polarization imager and tower crane and a fixed-point measurement method based on spectropolarimeter and bidirectional reflectance distribution function (BRDF) measurement frame were adopted to measure the multi-angular polarization distribution and local polarization homogeneity of the reflected radiation at the 490 nm and 670 nm bands in Dunhuang site. The results show that the reflected radiation from Dunhuang site possesses a certain degree of polarization characteristics. The polarization characteristics is wavelength-depended, the degree of polarization (DOP) of 490 nm band is obviously higher than 670 nm band, and the multi-angle polarization distribution is symmetric about the principle plane defined by the sun and instrument. In the principle plane, the DOP in forward scattering area (FSA) is higher than backward scattering area (BSA), and the DOP increased by the increasing of the view zenith angle (VZA). The angle distribution feature is fully consistent for the non-fixed-point method and fixed-point method. The local polarization homogeneity is about 6% for Φ100 m dimension area. The research on the polarization characteristics of reflected radiation from the calibration site is of great significance to the vicarious calibration scheme establishment and radiation measurement accuracy improvement.