Research On Flat Field Method Based On KLL Algorithm In X-ray And Extreme Ultraviolet Wavelength

The sun is the source of changes in space environment of the earth,and is the primary monitoring target of astronomical observation.The image data of observation in X-ray and extreme ultra violet(EUV)light of solar radiation is of great significance to the study in the internal mechanism of the sun and the monitoring in the space environment of the earth.With the development of space astronomy and the improvement of imaging instruments level in solar X-ray and EUV band,the quantitative image data is needed,and the effective flat field calibration method is necessary to ensure the data accuracy of imaging instruments in solar X-ray and EUV band.In this paper,the flat field method based on KLL algorithm is studied,which is suitable for solar X-ray and EUV band.It solves the problem that there is no uniform illumination source with a large area in this band,and provides a solution for flat field calibration of imaging instruments in this band on the ground and in orbit.Based on the study of KLL algorithm and its combination with image fusion technology in image processing,this paper proposes a method to obtain a flat field with high-precision and large field of view using only small displacement.By moving the sampling center to the edge to obtain compensated flat field images,and then weighting by the number of contributing pixels to smooth the stitching gap.It not only improves the precision at the edge,but also shortens the sampling time.In order to verify the performance of the method,both numerical simulation and real data are used in this paper.The relative error of full imaging plane is better than 0.1% in simulation experiment,and its RMS value of row is lower than 0.1%.The data of experiment is divided into three steps.The CMOS flat field experiment in visible light band testifies the feasibility of the method from the component-level and the system-level respectively.The flat field calibration experiment of the prototype of the solar X-EUV imager on the ground proves that the method is suitable for the solar observation equipment and also provides the flat field reference data for the on orbit flat field calibration of this equipment.Finally,adding specified displacements to the solar image data in 19.3nm band observed by SDO/AIA to simulate a shifting image sequence,the validity and stability of the algorithm for the solar imaging instrument in X-ray and extreme ultraviolet band are justified by the model.And the pixel-level relative error of this model is less than 3.0%,and its RMS value of row is about 1.1%.On the basis of studying the LSTM time series prediction model,this paper proposes and verifies a flat field change prediction method by using 30 groups of flat field sample data recorded by SDO/AIA for ten years.The prediction result is expressed by the mean value of 5 groups relative error of flat field obtained by prediction model,where both sets of the flat-field predictions are below 0.7%.This method can provide reference for on orbit flat field calibration of solar imaging instrument.