Fengyun-3E Solar Spectral Irradiance Monitor Quantitative Observation And Calibration Of The Sun

As the main source of energy for the earth,the sun continuously provides light and heat to the earth.Obtaining accurate and traceable radiation changes in the solar spectrum has important research significance and application value in the fields of heliophysics,atmospheric physics and environmental science.This paper deeply studies the development of solar spectral irradiance instruments at home and abroad,with analyzes the main functional principles and performance indicators of each instrument.Based on the Fengyun-3E Solar Spectral Irradiance Monitor Project,the quantitative observation and calibration of Sun was carried out.The Fengyun-3E Solar Spectral Irradiance Monitor developed by the Changchun Institute of Optics,Fine Mechanics,and Physics,is the first independently developed spaceborne hyperspectral solar irradiance instrument in China,which is used to obtain high-precision fine spectral irradiation data of 165nm～2400nm of the sun.This paper delves into the composition,function and working principle of solar irradiance spectrometer system,and analyzes the design of optical system and in-orbit working mode.Quantitatively analyze its core performance indicators including detector noise,signal-to-noise ratio,and stability.The results show that the system is dominated by the dark noise of the photomultiplier tube in the case of no illumination.Under light conditions,the system is dominated by anode shot noise.The signal-to-noise ratio of the spectrum in the visible band is about 600,about 30 d B;The signal-to-noise ratio in the infrared band is about 10,000,about 40 d B,which meets the requirements of instrument performance indicators.In this paper,a new high-precision convolutional on-orbit calibration method is proposed to monitor and correct the spectral position shift during SSIM in-orbit operation.Based on the SSIM observation data,the true solar spectral irradiance independent of the measuring instrument was obtained by convolution iteration of the higher precision reference spectral data HSRS and SSIM slit function,and the HSRS convolution results were matched with the solar spectrum measured by SSIM for onorbit spectral calibration,so that the maximum spectral offset did not exceed 0.03 nm,which met the wavelength accuracy requirements of 0.05 nm,which confirmed the feasibility of the high-precision convolution on-orbit calibration method for SSIM spectral calibration.Then,the convolution model is used to evaluate the accuracy of solar spectral irradiance data,which solves the problem that the spectral data sets cannot be directly compared due to different resolutions.Four independent and widely used solar reference spectral datasets covering ultraviolet to shortwave infrared are presented:Thuillier 2003,LASP WHI 2008,TSIS-1 SIM and TSIS-1 HSRS.The difference between the four solar reference spectra and the spectrum measured by SSIM was compared,and it was calculated that the total solar irradiance data measured by the SSIM integral average and the data used by the International Astronomical Union were about 0.1%,and the solar spectral irradiance measured by TSIS-1 SIM and SSIM has a small deviation from each other,with a deviation of about 5% in the ultraviolet band and within 2.5% in the visible and infrared bands.Finally,to solve the problem of optical system and detector performance degradation caused by the long-term adverse environmental impact of the spectrometer during orbit,based on the radiation transmission characteristics of SSIM and the international attenuation treatment method,the ultraviolet band attenuation function is established by second-order three-dimensional linear fitting to monitor the in-orbit attenuation characteristics of SSIM.According to the SSIM in-orbit operation mode,Curve Fitting was used to model the radiation attenuation of the filter,optical system,and subsequent detector.After comparing Gaussian fitting,Fourier fitting and linear fitting,it is found that the UV band attenuation function of the second-order threedimensional linear fitting has the best results,and the subsequent attenuation characteristics of the instrument are predicted from the model,and the fit degree is better than 99.7%.