Research On Measurement And Calibration Technology Of Spaceborne Relative Radiometer

Earth’s Radiation Budget(ERB)is one of the 54 Essential Climate Variables(ECV)determined by the Global Climate Observing System(GCOS).The ERB characterizes the balance of net radiation energy received by the Earth’s climate system,which directly affects global climate change.Long-term and continuous monitoring and recording of the ERB can also help us better understand the trends and patterns of global climate change,providing a scientific basis for global climate governance and sustainable development.Currently,the existing ERB measurement payloads mainly include the CERES from the United States,the GERB from Europe,the SIMBA from Belgium,and the ERM from China.Foreign radiation measurement payloads show a diverse development trend,including both the CERES,a polar-orbit NFOV scan radiometer,the GERB instrument on a geostationary orbit,and the WFOV radiometer,the nonscanning radiometer SIMBA.However,in China,only the polar-orbit NFOV ERM-1is used for ERB measurement,and the diversity of ERB instruments is insufficient.It is necessary to develop other types of ERB observation instruments to verify the effectiveness of ERB observation data through the comparison of data results from different instruments.In response to the measurement needs of the ERB in our country,this article proposes a spaceborne relative radiometer(SRR),which can simultaneously observe both solar radiation and terrestrial radiation on the same instrument,providing a new approach for measuring the ERB.The establishment of the measurement model for the SRR is crucial.This article analyzes the energy conversion throughout the measurement process of the SRR,starting from the blackbody radiation characteristics of the observed target,radiation energy propagation,and radiation thermal signal conversion.The structure of the radiation detector of the space radiometer is determined.Based on the detector’s structure,a measurement model for the SRR under a restricted field of view condition is established using network methods.This model is applicable to the measurement process of both the sun channel(SR)and earth channel(ER)of SRRThis article presents a detailed study of the measurement techniques of SRR instrument.Based on the instrument’s in-orbit operation mode,the scientific data products generated by SRR were preliminary evaluated,and the instrument’s technical specifications were determined.The different incident radiation energies on the SR and ER of SRR were analyzed,and in response to these differences and the observation scenarios,a parabolic reflector and Acktar black paint with high absorbance were used to increase the absorption rate of the SR,and an extinction-threaded aperture was designed to suppress the stray radiation of the ER.The suppression performance of stray light was verified through software simulation.The thermal connection structure of the thermal radiation detector was designed,and the temperature gradient on the detector under steady-state conditions was simulated and analyzed.An improved mathematical model of the thermistor was proposed for measuring the temperature gradient,providing a baseline for subsequent electronic design.To meet the measurement requirements of μV-level signals in radiation measurement,a preamplification system based on square wave lock-in amplification technology and a multi-channel data acquisition system based on voltage frequency converters were proposed and designed.The 1/f noise in the circuit was suppressed,achieving a 19.9-bit analog-to-digital conversion accuracy,ensuring the sensitivity of the instrument’s radiation observation.Additionally,the instrument’s in-orbit operational reliability was ensured through space environment adaptability design.Finally,research was conducted on the calibration technology of the space relative radiometer.Based on the observation characteristics of the brand-new Earth’s Radiation Budget instrument,SRR,an in-orbit comparison calibration scheme for the space relative radiometer’s daily channel was designed,and a ground verification method was proposed.By comparing and calibrating with a reference radiometer on the ground,the calibrated SR,1s and 2min surface solar irradiance data products were obtained,with an observation accuracy of 0.312%,and high time resolution surface solar irradiance data products were provided for scientific research.The performance of SR was verified,and the rationality of the in-orbit comparison calibration scheme was proved.A vacuum calibration scheme for the ER based on an extended-area blackbody source was designed,and the observation accuracy of the calibrated ER for blackbody emission radiation standard was verified to be better than 1.2%.