Field Calibration of Multiband High Resolution Imaging System with New Vacuum Solar Telescope

To achieve the filed matching of multiband images obtained by new vacuum solar telescope (NVST) with a high accuracy of 0.1 '', a method called pinhole aperture filed calibration is proposed and applied to the experimental analysis about the photosphere [TiO(705.8 nm)] channel and chromosphere [H alpha(656.28 nm)] channel of NVST. A pinhole-array aperture (11 x 11 pinholes) is used to the calibration of the rotation, scaling and translation relationships between the fields of the two channels. As a result, the high accuracy field matching of two-field solar images with the accuracy reaching up to 0.031 '' is accomplished by affine transformation. It is also found that the matching residual is not uniform in the entire field (about 2') and the maximum residual is about 0.076 '' at the edge of the filed. The values of the calibration parameters arc changing with the variation of optical platform position, and the matching difference of filed is 0.05 '', which is within the precision of the resolution requirement. The estimated accuracy is also supported by the analysis of measured data from TiO channel and H alpha channel.