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平场改正可以扣除日冕仪成像过程中的不均匀性,是其数据定标的必要步骤。提出一套基于乳白玻璃测量日冕仪平场的装置和方法,并开展了相关模拟和实地测量以验证该方法的可行性。首先,模拟了太阳经乳白玻璃后在日冕仪观测视场内扩散光源的均匀性,模拟结果表明其均匀度为99.98%,十分接近理想的均匀面光源。其次,测量了12cm地基日冕仪的平场,测量结果显示该方法可以测量出日冕仪成像的不均匀性,如探测器的条纹。平场改正后的结果符合日冕和天空背景亮度的径向分布。最后,为评价利用乳白玻璃测量平场的有效性,将其和天空平场进行了对比,二者相关系数为99.94%,线性拟合斜率为1,具有极强的相关性。
Flat field correction can deduct the non-uniformity of the coronagraphy imaging process, is a necessary step of data calibration. A set of devices and methods for measuring the corona flat field based on opal glass were proposed. Relevant simulation and field measurements were carried out to verify the feasibility of the method. First of all, the uniformity of the diffused light source in the observational field of the coronagraph was simulated after the milk was passed through the milky white glass. The simulation results show that the uniformity of the light source is 99.98%, which is very close to the ideal uniform light source. Secondly, the flat fields of the 12cm ground-based coronagrams were measured. The results show that this method can measure the inhomogeneity of the coronal instruments, such as the stripe of the detector. The result of the flat field correction is consistent with the radial distribution of the brightness of the background of the corona and the sky. Finally, in order to evaluate the effectiveness of measuring the flat field with milk white glass, the comparison was made with the sky flat field. The correlation coefficient was 99.94% and the linear fitting slope was 1, which showed a strong correlation.