Simulation Study Of Geometric Distortion In Astronomical Image

The Geometric Distortion(GD) is an error that generally exists in the optical system of an astronomical telescope. The CCD image position of targets can shift when affected by this error. Especially in astrometric research, the GD error have great effect on astrometric positional precision. To obtain high precision astrometric data, it’s important to correct the GD effects. In addition, the precision of GD pattern would also affect the astrometric precision. So the factors which have influence on the GD residuals should be studied, as well as the method used to solve GD.In this paper, 58 frames of CCD image obtained by the YFOSC attached to the 2.4 m telescope at Yunnan Observatories are processed. The GD effects in position of reference stars are then be corrected after solving the GD pattern using a method proposed by Peng et al. The results show that the GD errors are within a range of ±2 pixel and most of GD residuals are within a range of ±0.02 pixel after correcting the GD errors. However, a systematic tendency can be found in the results.As such, the factors that influence the GD residuals are studied using a simulation experiment. There are two factors which are the FWHM of a stellar image profile and the space period of GD function have been studied. To be specific, the GD residuals affected by different values of factors are studied in a way that the value of one factor is changed when the other is set to be constant. The results show that the GD residuals grow bigger when the FWHM of a stellar image profile becomes bigger or the period of GD function becomes smaller.In addition, the method of solving GD is also studied using simulation experiment. 44 frames of CCD image obtained by the YFOSC attached to the 2.4 m telescope at Yunnan Observatories are processed. After the catalog position of reference stars are used to obtain simulative data which are distortion free, an early solved GD pattern is added to the simulative data, also with the catalog error and the measurement error added. Then the GD pattern is solved once again using these distorted simulative data. The comparison and analysis between the early solved GD pattern and the solved GD pattern of simulative data show that the biggest difference is 0.28 pixel, the mean difference is 0.10 pixel and the standard deviation is 0.05 pixel.