中国科学院云南天文台机构知识库

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 remove the non-uniformity in the coronagraph imaging process, which is a necessary step in its data calibration. The device and method for measuring flat-field of coronagraph based on an opal glass are proposed in this paper. Some simulations and site measurements are carried out to verify the feasibility of this method. First of all, the uniformity of the diffused sunlight passing through the opal glass in the field of view of the coronagraph is simulated. The simulation result shows that its uniformity is 99.98%, which is very close to the ideal and uniform area source. Moreover, the flat-field of the 12 cm ground-based coronagraph is measured. The observational result indicates that the non-uniformity of the coronagraph imaging can be observed with this method, such asthe fringes on the detector. The result after flat-field correction agrees well with the radial distribution of the background luminance ofcoronagraph and sky. Lastly, the flat-fields from the opal glass are compared with the sky flats in order to evaluate the validity of flat-field measurement with opal glass. Their correlation coefficient is 99.94% and the corresponding linear fitting slope is 1, which shows a strong correlation.