High-resolution solar image reconstruction based on non-rigid alignment

Abstract Suppressing the interference of atmospheric turbulence and obtaining observational data with high spatial resolution is an important problem to be solved in ground observation. One way to solve this problem is to perform statistical reconstruction of short-exposure speckle images. Combining the advantages of the classic Shift-Add and speckle masking algorithms, this paper proposes a novel reconstruction algorithm-NASIR (Non-rigid Alignment based Solar Image Reconstruction). NASIR performs pixel-by-pixel non-rigid distortion correction on speckle images by establishing a computational model between geometric distortion and intensity distribution, thereby reconstructing the phase of the object image at each frequency. We compared the reconstruction performance of speckle masking and NASIR in terms of correlation coefficient, power spectrum and intensity profile variation coefficient through reconstruction experiments of NVST (1m New Vacuum Solar Telescope) observational data. The results show that when seeing is good (R0>10cm), both speckle masking and NASIR can achieve better reconstruction results. When seeing decreases (R0<5cm), the noise will exacerbate the phase recursion error of speckle masking, resulting in the generation of spurious structures, while NASIR recovers the phase by spatial alignment, which can avoid error accumulation. Moreover, NASIR performs speckle interferometry on the aligned speckle images, which further improves the reconstruction quality of the modulus, so its reconstruction results have a higher cutoff frequency and more significant structural contrast. In addition, NASIR reconstruct the entire field of view in parallel at one time, without phase recursion and block-by-block reconstruction, so its computation time is only about 50% of that of speckle masking. Therefore, we consider NASIR to be a more robust and efficient method that combines the respective advantages of spatial domain reconstruction and frequency domain reconstruction. It is believed that the application and further research of NASIR will promote the development of ground-based observation data processing technology.