针对2019年11月发射的首颗民用亚米级高分辨率立体测绘卫星高分七号的影像数据特点,2020年9月在内蒙古包头高分辨率遥感综合定标场开展了卫星在轨辐射定标试验。利用包头场固定辐射灰阶靶标和AERONET AOE-Baotou站点同步观测反演的大气气溶胶物理及光学特性参数,基于反射率基法对高分七号卫星传感器进行了在轨场地绝对辐射定标,获取了卫星在轨辐射定标系数,实现了传感器全动态范围内的高精度辐射定标。同时基于包头场均匀沙地的自动观测数据对辐射定标系数进行了精度验证。试验结果显示,高分七号卫星自发射以来立体测绘相机的辐射性能稳定,相机各波段影像DN值与表观辐射亮度的线性相关系数优于99%。通过误差分析可知,高分七号卫星包头场辐射定标的不确定度优于5%,获取的定标系数精确可靠,获取的辐射定标系数可用于地物参数的反演,对实现我国国产立体测绘卫星数据定量化应用、提高定量遥感科研水平都具有重要意义。

The aim of our study is to obtain a reliable and high-precision radiometric calibration coefficient for GF-7 satellite sensor. In this paper, we describe the methods and results of a reflectance-based vicarious calibration campaign that was conducted in September 2020 at RadCalNet Baotou Site, located in the Inner Mongolia, China. A series of gray-scale permanent artificial targets and infrastructure has been built in the Baotou site to provide effective support for GF-7 satellite sensor on-orbit calibration. The reflectance-based vicarious calibration approach relies on the synchronous measurement of the surface spectral reflectance and atmospheric parameter. In this campaign, the synchronous measurements of surface and atmospheric conditions (included the aerosol optical depth, amount of water vapor, aerosol inversion products) at Baotou site at the time of GF-7 satellite overpass were obtained by SVC HR-1024i spectroradiometer and Cimel CE318 sun photometer. The bidirectional reflectance distribution function(BRDF) of the surface was measured by multi-angle instrument with SVC spectroradiometer. The synchronous measurement of the surface spectral reflectance was modified by surface BRDF model and the atmospheric parameter are coupled with exoatmospheric solar irradiance spectrum and relative spectral response of sensor as inputs into a radiative transfer model to compute the at-sensor spectral radiance. The relationship between the at-sensor radiance and the DN recorded in the GF-7 satellite image is identified. The results reveal a good linear relationship between the digital number (DN) and the apparent radiances of each band. The uncertainty of the GF-7 sensor radiometric calibration in the RadCalNet Baotou site is 4.33%, less than 5%. A detailed discussion on the validation analysis of GF-7 radiometric calibration coefficient using the products from the automated RadCalNet Baotou Sand site. This study can also supply site reference to the radiometric validation for Chinese Satellites. Considering the results shown in this work, the data from RadCalNet Baotou site can be used as a reference to evaluates the radiometric performance of Chinese High Resolution satellite.