A Study of Influences of Atmospheric Dispersion on the Multi-Waveband Synchronous High-Resolution Reconstruction Applied to Solar Images

The New Vacuum Solar Telescope (NVST) at the Fuxian Solar Observatory (of the Yunnan Observatories) is currently equipped with a two-channel imaging system, which enables the NVST to simultaneously collect solar images at the wavelengths of the Tio and H-α lines. Plans have been made to extend the number of channels of the imaging system to five. The extension will inevitably increase the amount of calculations required for image reconstruction. This, coupled with the calculation-intensive speckle-masking method used for the NVST, can potentially result in calculations beyond what the current systems can handle within reasonably short times. In this paper, we present a new image-reconstruction method, termed as the Solar Multi-Waveband Synchronous High-Resolution Reconstruction (SMWSHRR). The SMWSHRR first estimates the PSF of a channel at which data have relatively high signal-to-noise ratios (SNRs), then by applying wavelength corrections to the PSF obtains the PSF of each other channel. With the evaluated PSFs it finally deconvolves images of all channels simultaneously to save time. Using the data of high SNRs as the basis gives the method an advantage of improving the reconstruction accuracy. However, the method assumes that light rays of all relevant wavelengths follow the same atmospheric path. Practical patterns of light-ray paths deviate from the assumption, and effects of deviations on reconstruction results need to be studied. In this paper, through simulations of turbulences in multiple layers of the atmosphere we analyze influences of atmospheric dispersion on results of the SMWSHRR. The analyses are based on comparisons of the wavefront aberrations caused by atmospheric dispersion, the relative spectral ratios, and the reconstructed images at different zenith-angle values. Our results show that for a 1m solar telescope as the NVST, atmospheric dispersion at most weakly affects results of the SMWSHRR in near-infrared and visual wavebands as long as the zenith angles are less than 60°, except that result resolutions at 393.3nm will be appreciably reduced if zenith angles are above 45°.