| The sun is the source of energy for the earth's climate system.Total Solar Irradiance represents the amount of electromagnetic radiation energy input by the sun to the earth's climate system.In order to study the causes of climate change,accurate and continuous observations of the total solar irradiance are necessary.The absolute solar radiometer based on the principle of electric substitution can directly calibrate the radiation value and has become a standard measuring instrument for the total solar irradiance in orbit.At present,the space-borne absolute solar radiometer includes DIARAD(Belgium),TIM(USA),PREMOS(Switzerland)and SIAR(China),and there is an absolute difference about 0.35% between the total solar irradiance series of each instrument.Therefore,it is necessary to research on the differences among the instruments,the technical problems about the instrument design,characterization and calibration of the SIAR,improve the calibration ability of the instrument on-orbit,and provide high-precision and traceable scientific data for meteorological research.Firstly,we analyzed the measurement principle of SIAR.In order to prevent the outside stray light from the field of view,we put forward the two levels of optical system,designed the front window aperture stray light effect reduced to 1.3 PPM.In order to reduce the measurement period,the low thermal capacity detector and high heat conductivity thermal connection structure were designed,the new cavity detector time constant was reduced by 63%.A temperature control method based on PID mode was designed,and the fluctuation of sampling code value was reduced by 80%.The tracking method based on constant current chopper digital subdivision was proposed,and the ground-based analog tracking deviation was less than 0.015°.Then based on the parameter characterization to accurately evaluate the performance of the instrument and the establishment of a traceable to SI,the characteristics of temperature to the aperture area modeling analysis and uncertainty evaluation;The common optical path method was designed to calibrate the absorption rate of blackbody cavity.The diffraction effect of the instrument was evaluated based on SAD model.The temperature correction model was established to calibrate the temperature characteristics and attenuation characteristics of the parameters such as the reference voltage and the heating wire resistance in the laboratory to solve the problem of in-orbit temperature correction.The cold background radiation compensation model was established and the ground verification was designed.The calibration and evaluation of all 12 parameters were realized.The relative uncertainty of three channels of the SIAR was better than 0.06% by the laboratory light source.Finally,the field comparison against WRR and the calibration of vacuum air inequivalence were carried out.The WRR standard was established based on multiple transfer radiometers,and a two-dimensional tracking turntable was designed to realize synchronous tracking and measurement by multiple instruments.The consistency and linearity of the measurement results of the radiometer were analyzed,and the data were corrected based on the temperature model.The calibration accuracy of three channels of the SIAR relative to WRR was better than 0.1%.The photoelectric inequivalence of the instrument in the air and vacuum environment and its causes were analyzed.The solar parallel light was introduced into the vacuum tank by using heliostat as tracking mechanism.The normalized alternate comparison method was proposed to measure the irradiance synchronously in the vacuum and air condition.The air-to-vacuum relative coefficient of SIAR solar absolute radiometer was obtained for the first time,and the measurement results in-orbit can be traced to the world radiation standard. |
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