The Research Of On-board Calibration Method Based On Double-solar Diffusers

On-board calibration based on solar diffuse with very stable sunshine illuminating solar diffuse of which the BRDF is known,forming an approximate lambertian surface light source with a known radiance filled with the remote sensor field of view,can achieve all-optical path?end-to-end absolute radiation calibration.It has now become one of the main development direction of on-board calibration for its high precision,high frequency,high efficiency characteristics and has been successfully applied to MODIS,MERIS and other satellite load on-orbit calibration.Solar diffuse stability monitor(SDSM)is used to monitor the attenuation of solar diffuse BRDF and a solar attenuation screen is used to attenuate the incident luminous flux to achieve the matching of the calibration time and the energy of the ground observation time,however,too much rotation mechanism will adversely affect long-term calibration;A reference solar diffuser Double is used to monitor the attenuation of the calibration diffuse reflector,While observing different goals remote sensor entrance pupil energy has a large difference,the detector dynamic response range is large,So it will bring some error for calibration,and the volume,weight larger;Based on the successful experience of two kinds of calibration methods,the "double solar diffuser + solar attenuation screen" on-board calibration method is putted forward,using the remote sensor to be calibrated to observe the solar diffuse reflector,making the observation angle and field of view consistent,to improve the accuracy of star calibration,and reducing the rotation mechanism,matching the energy,thereby improving the accuracy of star calibration.According to the new on-board calibration system,the on-board reflectivity and absolute radiation calibration model are established.BRDF and attentuation screen transmittance real-time value at the time of calibration is the key parameter to determine the calibration accuracy,which can be determined by the ground measurement value combined with the established BRDF attenuation monitoring model and the specific orbital parameters,so the pre-launch BRDF and transmittance need to be accurately measured in the ground laboratory,the degradation model of the solar diffuser based on the calibration times.Based on the time series ratio?based on the wavelength ratio and time-wavelength integrated attenuation monitoring model are established,the BRDF attenuation monitoring accuracy is improved Their performance have been tested for accuracy and.A solar diffuse and solar decay screen are designed and produced,Bidirectional reflection distribution function test result shows that the two solar diffuse BRDF has a good consistency and Lambertian,and the uncertainty is better than 1%,Satisfying the requirements of the star calibration,for ensuring long-term star calibration accuracy has a very important significance;The results show that the transmittance of the solar attenuation screen is 13.8%and the test uncertainty is better than 0.54%(K=2);finally the calibration accuracy of the star scale is given as follows:the reflectivity calibration is better than 1.9%...