采用比辐射计进行比对测量是监测光学遥感仪器星上定标光源载体漫射板反射性能在轨变化的有效手段。用于海洋水色遥感的新一代星载成像光谱仪必须设计成以太阳作光源的在轨绝对辐射定标系统，才能满足定量化产品反演的使用要求。国外星上定标器的漫反射板长期跟踪测量结果表明，漫射板的反射性能一直在发生变化，且波长越短变化越大，而海洋水色遥感要素的探测恰恰集中在靠近紫外的波长区域。针对这个问题，设计了分谱比辐射计，并对其辐射探测性能进行了理论分析与实验测量。结果表明，在整个动态测量范围内线性相关系数优于0.9991，在轨输入能量条件下的分谱信噪比在整个使用波长范围内优于100，可以满足成像光谱仪星上定标源反射特性标定的精度要求。

For a diffuser which is used as the light source carrier for in-orbit calibration of an optical remote sensor, to use a ratioing radiometer to monitor the variation of its reflection performance in orbit is an effective means. In order to meet the inversion requirement of quantitative products, the absolute radiation in-orbit calibration system for a new generation of spaceborne High Resolution Imaging Spectrometer (HRIS) should be designed to use the sun as its light source. The long-term tracking measurement results of a foreign in-orbit calibrator show that the reflectance of the diffuser is changing all the time. Moreover, the shorter the wavelength is, the greater the change is. However, the remote sensing of ocean color elements just concentrates on the wavelength region close to UV. To solve this problem, a spectrum ratioing radiometer is designed. Its radiation detection performance is analyzed theoretically and measured experimentally. The results show that its linear correlation coefficient is better than 0.9991 in the whole dynamic measurement range and its spectrum signal-to-noise ratio under the in-orbit irradiation input condition is better than 100. It can meet the calibration precision requirement of the reflection performance of the spaceborne diffuser for a spaceborne HRIS.