Design and Verification of Ratioing Radiometer Parameters

Ratioing radiometer, which is a key part for improving the precision of on-board calibration facility, can be used to track and correct on-orbit degradation of solar diffuser. In this paper, an on-board calibration facility with solar diffuser is presented and the model of BRDF correction for solar diffuser is established based on the principle of ratioing radiometer. For the purpose of optimizing the performance of ratioing radiometer, the output of solar diffuser view and sun view should be matched. Considering that the solar illumination angle changes in different season, the ratio between signals from solar diffuser view to sun is designed to range from 0.899 to 1.692, and 1.296 at intermediate incident zenith angle. In order to verify the designed ratio, testing equipment is built on the basis of relative lamp-illuminated plaque system, where the lamp and plaque simulate the sun and solar diffuser, respectively. The result shows that the ratio is within 0.5% error of the designed value. Factors that could induce the testing error are discussed. The above results show that the design parameters of ratioing radiometer are reasonable which meet the requirements of on-orbit degradation monitoring for solar diffuser.