ABSTRACT
As the reference radiometric calibration standard of sensors on the Haiyang-1C (HY-1C) satellite platform, the satellite calibration spectrometer (SCS) is equipped with an onboard calibration system composed of double solar diffusers and an erbium-doped diffuser to monitor the postlaunch radiometric response change. Herein, through onboard calibration data analysis, the calibration diffuser performance remains stable without degradation, and the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra is adopted as a reference to repeatedly verify onboard radiometric calibration results by selecting different dates and reflectance scenes. The SCS equivalent reflectance is obtained by combining the mean digital number (DN) of the SCS crossing area image with the radiometric calibration coefficient. The spectral reflectance is obtained via interpolation and iteration, which is adopted as the actual MODIS incident pupil spectral reflectance because the small imaging time interval can be ignored and almost vertically observed, and it is convoluted with the MODIS spectral response function to obtain the predicted equivalent reflectance. Validation is completed by comparing the predicted MODIS equivalent reflectance to the measured value based on the onboard calibration coefficient. The results show that (1) the difference between the measured and predicted MODIS band equivalent reflectance is between -0.00466 and 0.0039, and (2) the percentage difference between the measured and predicted MODIS band equivalent reflectance ranges from 4.17% and 1.24%, indicating that the calibration system carried on HY-1C can perform high-precision SCS radiometric calibration, meeting the cross-calibration accuracy requirements of other loads on the same platform.
ABSTRACT
As one of the most important ways of improving the calibration accuracy at present, the calibration method based on a solar diffuser(SD) is an independent calibration way with advantages of high accuracy, high frequency and high efficiency . The principles, methods and implementation process of on-orbit calibration based on the SD is described in this thesis. The radiance reference for calibration in space is found and the physical model of the on-orbit reflectance calibration is provided. The main factor which affects the calibration uncertainty is the determination of the SD bidirectional reflectance distribution function (BRDF) value by analyzing the physical models of on-orbit calibration. Thus, the timing selection of the on-orbit calibration is introduced and the BRDF in the range of angles variety within the calibration timing is tested in the lab. During the on-orbit calibration time, the high accuracy on-orbit calibration in the remote sensors' whole life is achieved by the accurate radiance input which is ensured by monitoring and correcting the SD BRDF value from its fabrication to its life end. Finally, the on-orbit calibration uncertainty is estimated based on the measurement levels of the parameters in the physical model. And the uncertainties of on-orbit reflectance calibration and method of radiance calibration are better than 2.03% and 2.04% by type B standard uncertainty evaluation method.
