Research On Solar Atmosphere Line-of-sight Velocity Measurement Technology Based On Spectrum Scanning Imaging

The influence of space weather on our production and life is becoming more and more obvious.Solar activity is the source of space weather event.It is of great significance to forecast space weather by monitoring solar activity.The solar atmospheric line-of-sight velocity field represents the solar atmospheric line-of-sight motion,which is an important part of solar activity monitoring.Because of the advantages of large field of view and high time cadence,the measurement method of solar atmospheric line-of-sight velocity field based on spectral scanning imaging has been widely used.Among them,Lyot filter with the advantages of large field of view,good stability and mature technology has become the most important spectral scanning equipment.In this paper,we focus on the spectral scanning imaging system with Lyot filter,and study the measurement technology of solar atmospheric line-of-sight velocity field as follows:Firstly,the principle of spectral scanning imaging of Lyot filter and the systematic errors related to the measurement of solar atmospheric line-of-sight velocity field are studied and analyzed.The results show that the measurement errors of Lyot filter system mainly come from the design error of filter,the design error of optical path and the field of view effect caused by various errors.Errors can be reduced by various means and measured and corrected by on-line calibration.A new method for online calibration of Lyot filters is proposed.This method uses joint observation of monochrome imaging channel and spectral scanning imaging channel to correct the vary of solar intensity in the calibration experiment,the influence of time-varying solar intensity on the calibration results is reduced.The experimental results show that the scanning contour of the Lyot filter spectral scanning imaging system is in accordance with the theoretical contour,the offset of the contour center is less than 0.005 nm,and the corresponding Doppler velocity error is less than 2 km/s.Secondly,two kinds of solar velocity field inversion algorithms based on spectralscanning imaging data are studied,and the effects of the number of spectral scanning wavelength points and the spectral scanning wavelength interval on the performance of the algorithm are analyzed.The results show that the effective dynamic range of Fourier phase inversion algorithm and centroid inversion algorithm is limited by the number of spectral scanning wavelength points and the spectral scanning wavelength interval.To this end,the correlation method is proposed.The results show that the computational errors of the correlation method are much smaller than those of Fourier phase method and centroid method in the effective dynamic range,and the computational errors can be controlled within 2% of the real speed.The correlation method is with higher computational accuracy.Finally,the process of a typical small flare is observed and analyzed in detail.Based on the observed data of six wavelength scanning positions at the time of small flare eruption,the line-of-sight velocity is calculated using the correlation algorithm.The evolution of the velocity field during the eruption process is explained theoretically based on the results of solar observation,and the validity of the correlation algorithms is preliminarily verified.In this paper,the measurement technology of solar atmospheric line-of-sight velocity field based on spectral scanning imaging is studied comprehensively and deeply,which provides a new solution and realization scheme for more accurate measurement of solar atmospheric line-of-sight velocity field.