长时序、高频次的辐射定标是跟踪和校正星载光学遥感器在轨响应变化的基本手段，辐射校正场地表方向反射特性是影响多角度、宽视场的非垂直观测载荷辐射定标精度的关键因素。针对地表方向特性季节性变化但却缺乏有效数据的瓶颈问题，开展地表方向特性时变模型方法研究。通过地表多角度方向特性自动测量技术的研究和设备改造，获取辐射校正场地表多角度的长时序基础观测数据，实现全季节地表半经验BRDF时变模型的构建，重点开展天空各向异性对地表长期测量的影响分析、地表方向特性的尺度效应等技术难题的攻关，并对影响模型精度的地表均匀性、角度定位准确性、参考板朗伯性等因素进行量化评价，最终通过对多遥感器辐射定标的定量化应用，验证地表时变模型的长时序精度和稳定性。项目的开展能够积累大量有效的地表多角度方向特性观测数据和有效的时变模型，为我国的大气、环境空间观测体系的长时序定量遥感和多遥感器跨平台联合观测提供不可或缺的技术支撑。

Long time series and high frequency radiometric calibration is a basic means to correct the change of the optical satellite sensors on-orbit. The surface directional reflectance is the key factor affecting the accuracy of non-vertical observation satellites with multi-angle and wide field of view. To resolve the problem of the surface directional reflectance changing with time but lacking effective data, the research on the surface directional time variation model based on field automation observation would be carried out. With the surface multi-angle directional characteristic automatic measurement technology, the long-term observation data of the radiometric calibration sites is obtained, and the surface BRDF time-varying model of the whole season is constructed. The key influence of the sky anisotropy and the scale is analyzed. The factors affecting the accuracy of the model such as surface uniformity, angular positioning accuracy, reference plate Lambert would be estimated. Through the radiometric calibration application of satellite sensors, the long-term accuracy and stability of surface time-varying model is verified. A large number of effective observation data of surface multi-angle direction characteristics and time-varying model can be accumulated, which would provide the indispensable technical support for the long-term quantitative remote sensing and the multi-sensor cross-platform observation of China's atmospheric and environmental space observation system.