Research On Key Technologies Of High-precision Solar Irradiance Spectrometer

As an important payload on FY-3 meteorological satellite,solar irradiance spectrometer measures the solar spectral irradiance through three channels,ultraviolet/visible/near infrared,to obtain the characteristics of solar spectral irradiance.The instrument captures the impact of solar activity on spectral irradiance,which is used for research on solar physics,atmospheric physics and climate physics.In addition to supporting units such as guide mirror,turntable,electric control box,ultraviolet spectrometer(UV)and visible/near infrared(VIS/NIR)spectrometer are the core units of Solar irradiance spectrometer.High precision,wide spectral band and high integration are the characteristic of the two spectrometers.The service life of the instrument on-orbit is 8 years.The key problem in the design and development of solar irradiance spectrometer is to solve the problem of high-precision spectral detection in a wide spectral range and meet the requirement of long-term stability.Started with analysis of structure,design of wavelength scanning mechanism,system integration scheme and calibration correction method are put forward,so as to break through the key technologies of high-precision highly integrated dual channel spectrometer,which provides guarantee for obtaining high-resolution solar spectral irradiance data.Specific contents as follow:1)Design and accuracy analysis of high-precision wavelength scanning mechanismIn order to meet the requirements of hyperspectral resolution,satellite resource limitation and reliability index of solar spectrometer,plenty research of wavelength scanning mechanisms from domestic and abroad are analyzed and compared.Oil lubricated lead screw and bar mechanism is determined.Preload structure and positioning mode of the lead screw are optimized,which improves the positioning accuracy of the lead screw.According to the structural design,driving formula of the wavelength scanning mechanism is deduced.The mechanical index of lead screw length is given as follows:leadscrew length 55mm,absolute positioning accuracy 5?m,repeated positioning accuracy 1?m,which provides a theoretical basis for determining the system scheme of spectrometer.Through the comprehensive error analysis of the wavelength scanning mechanism,it is calculated that the spectral repeatability of the solar spectrometer is better than ±0.05nm,and the spectral measurement error is no more than ±1.227nm.The theoretical analysis is consistent with the measured results.2)Research on high precision integration technology of spectrometer systemAccording to the structural characteristics of four grating coaxial and symmetric optical system,two core integration technologies,four parallel beam method and bilateral debugging method,are proposed,which meet the requirement of high precision of spectrometer.The precision integrated instrument ensures sufficient energy output on the premise of high spectral resolution.a.Four parallel beam method:Divided into four beams,a laser beam is reflected and self-collimated to form a parallel beam,which realizes the accurate calibration of the four-grating position.And the mutual angle error after grating integration is better than 1.7',which meets the system requirements;b.Bilateral debugging method:two reference beams are used to accurately calibrate each optical element,so as to reduce the difficulty of connecting optical path and adjust the relative position of each component more accurately.3)Study on nonlinear analysis and correction method of spectral calibrationIn view of the two main factors causing the spectral nonlinearity in the process of system integration,the angle adjustment error of slider and the angle adjustment error of gratings,the mechanism of spectral nonlinearity is analyzed.And the corresponding methods are adopted to compensate the nonlinear errors.The specific spectral calibration formula is derived through high-order polynomial fitting or incorporating error term.It is successfully applied to the spectral calibration of the integrated spectrometer.The calibration accuracy after correction is improved from 0.08nm to 0.03nm,which meets the requirements of the system.4)Analysis of temperature characteristics of wavelength scanning mechanism and spectrometer systemIn this paper,the wavelength drift characteristics of the spectrometer caused by temperature rise of the wavelength scanning mechanism are analyzed.A model of Onorbit correction method for spectral drift is constructed.a.Analysis of temperature induced wavelength drift of wavelength scanning mechanismAccording to the structure and working principle of the wavelength scanning mechanism,influence of temperature change of wavelength scanning mechanism on spectral measurement accuracy of spectrometer is analyzed.Using the temperature homogenization finite element model,temperature sensitivity of mechanism parts is analyzed.Relationship between thermal deformation and wavelength drift is deduced.And the conversion equation of temperature variation and wavelength drift of wavelength scanning mechanism is constructed.The accuracy of the conversion equation is verified by the test results.b.Study on quantitative analysis and correction method of spectral driftIn order to adapt to the space environment,vacuum heat balance test is carried out on Solar spectrometer.Temperature of the single monitoring point is used as the dynamic representation of the structure temperature.Conversion equation between the mechanism temperature rise and spectral drift is derived.And the quantitative correction model of the temperature drift of the solar spectrometer is constructed.Compared with the results of vacuum calibration test,the feasibility of the correction model is proved,which provides a basis for the on-orbit wavelength correction of the instrument.With the research on the key technologies of solar spectrometer,the wavelength repeatability of UV spectrometer is better than 0.01nm,the wavelength calibration accuracy is better than 0.05nm.The wavelength repeatability of VIS/NIR spectrometer is better than 0.05nm,and the wavelength calibration accuracy is better than 0.1nm.It has reached the international advanced level of similar instruments.