| In space environment observation,the research of solar physics has always been the focus of many scholars,especially in recent years exploring solar extreme ultraviolet(EUV)bands is a new research direction for scholars,that has very important significance for the future of humanity.However,in the process of observation,the space weather disturbance,the spacecraft's orbit attitude precession and the rotation of the moving parts can cause the random vibration of observation platform,resulting in blurred images and affecting the high precision imaging of the telescope.At present,extra equipment is usually used to detect the movement of the platform,which makes the structure design complicated and the reliability reduced.With the rapid development of image processing technology,it has become a reality to use solar EUV images sequence to directly detect platform jitter.This method can save resources,but also increase the reliability of measurement,with small errors in compact structure.Therefore,this paper conducts in-depth research on key technologies such as improving displacement detection efficiency and accuracy,the study of the displacement measurement of the local field of the EUV images of the solar can help astronomers to understand the local motion of the solar more accurately and observe the detailed structure of the EUV images of the solar more clearly.First of all,in the integer pixel displacement search methods,the global search method needs to search the whole image point by point,and the search efficiency is very low,while the ordinary four-step search method may fall into the local optimal during the search process,and this paper proposes an improved four-step search method to solve these problems.At the same time,the existing integer pixel search method will carry out correlation calculation for all points in the subset image,so as to obtain the peak of correlation operation,which leads to a significant increase in computation time.Therefore,this paper proposes to use two low-order invariant moments representing image features for correlation calculation,so as to solve the problem of low efficiency caused by all points in image subset participating in correlation operation.Through experimental comparison,the integer pixel search time of the method in this paper is in the order of milliseconds,which is two orders of magnitude higher than the global search time,and comparing with the whole pixel displacement search method by seven invariant moments,the search efficiency of this method is improved by an order of magnitude.It can be seen that the integer pixel displacement search efficiency of this algorithm is significantly improved.Secondly,in the study of high-precision sub-pixel displacement measurement,a number of influencing factors in the process of taking solar EUV images by polar ultraviolet imager are analyzed,such as the evolution of solar coronal atmosphere,precession jitter of orbital platform,and non-uniformity of imaging instrument.A three-order nonlinear iterative model based on the first-order form function is proposed to calculate the sub-pixel displacement velocity of the solar EUV images,and the solution process of the model is theoretically derived in detail,and the specific expression of the iterative solution is obtained.The experimental results show that the accuracy of sub-pixel displacement measurement in the quiet region,the active region and the coronal hole region of the solar EUV images is 0.01 pixels,0.1 pixels and several pixels respectively.The results show that the accuracy of image displacement measurement by using the first order function is about one order higher than that by using the zero order function.The accuracy of this algorithm is an order of magnitude,1.5 times and 1.2 times higher than that of the curved surface fitting method,the linear iterative algorithm and the quadratic nonlinear iterative algorithm for measuring the sub-pixel displacement of solar EUV images,and it is fully verified that the algorithm has high precision of sub-pixel displacement measurement.Thirdly,the influencing factors of solar pole ultraviolet image displacement measurement accuracy are deeply studied,and based on the nonlinear iterative model of first-order form function,the specific analytical expression of displacement measurement error is derived,which indicates that the precision of displacement measurement is closely related to the average gray scale,average gradient and subset size of image subsets.The parameters suitable for evaluating the displacement measurement accuracy of solar EUV images are proposed,namely comprehensive consideration of mean subset intensity and gradients(CCMSIG),the smaller the value is,the higher the displacement measurement accuracy is.By analyzing the relationship between image subset CCMSIG value and image subset size,an optimal selection method of image subset size based on image subset CCMSIG value is proposed,this method improves the calculation efficiency,but also reduces the size of the subset of the image,while ensuring the accuracy of displacement measurement.Finally,through detailed analysis and research on the distribution forms of different regions of the solar EUV images,the experimental samples were designed to simulate the distribution of the real images,and the whole photoelectric system for displacement measurement was built.The experimental results show that the displacement measurement accuracy obtained by using this measurement system is consistent with the corresponding displacement errors obtained by using real solar EUV images;Meanwhile,in the process of the experiment,a four-quadrant detector is adopted to measure the corresponding displacement,which serves as a comparative verification experiment,and the results show that the displacement error obtained by using the experimental sample area one is consistent with the displacement error measured by the four-quadrant detection.Thus,the feasibility of using the displacement measurement photoelectric system to simulate the displacement measurement of solar EUV images is verified,and the correctness and effectiveness of the method proposed in this paper are also verified.The method proposed in this paper can be applied to the displacement measurement of the local field of the solar EUV images,which has important practical significance. |
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