An Experiment of CCD Frame-Combination

In order to obtain astronomic images with a wide field of view and high precision, a method of combining a few CCD (Charge Coupled Device) frames taken by a telescope is performed in this thesis. Peng et al.'s geometric distortion model is used to correct original images during the pre-processing phase. Coordinate transformation from original images to the final combined frame uses a six-parameter model together with the Catalog UCAC4. Unlike hardware image mosaic, the gray value of each pixel in the original frame needs to be redistributed to the pixels of a unique reference frame. The algorithms of this frame-combination are described in detail in this article. Furthermore, this method has been tested with many CCD frames taken by the 2.4m Telescope at Yunnan Observatories. Results show that this method can yield a quite good CCD frame with a wide field of view. Specifically, moving objects can be detected easily; in terms of faint ones, there is significant improvement in their SNR (Signal to Noise Ratio) as well. Test results also show that the star positional errors introduced by the frame-combination are reduced to about 0.02 pixels when raw CCD frames are corrected for their geometry distortions. This experiment therefore confirms the validity of Peng et al.'s geometric distortion solution and the necessity of correcting geometric distortions.