空间望远镜图像天体测量定标--以“卡西尼”窄视场照相机为例  

Improved astrometric calibration of Cassini narrow angle camera images and its accurate geometric distortion model

作　　者：郭碧峰 彭青玉[1,2] 陆星 郝佳男[1,2] GUO BiFeng;PENG Qing Yu;LU Xing;HAO JiaNan(College of Information Science and Technology,Jinan University,Guangzhou 510632,China;Sino-French Joint Laboratoy for Astrometry Dynamics and Space Science,Jinan University,Guangzhou 510632,China)

机构地区：[1]暨南大学信息科学技术学院,广州510632 [2]暨南大学中法天体测量、动力学与空间科学联合研究实验室,广州510632

出　　处：《中国科学：物理学、力学、天文学》2023年第4期112-122,共11页Scientia Sinica Physica,Mechanica & Astronomica

基　　金：国家重点研发计划(编号:2022YEE0116800);中国载人航天工程巡天空间望远镜专项科学研究项目(编号:CMS-CSST-2021-B08);国家自然科学基金(编号:11873026,11273014);国家自然科学天文联合基金重点项目(编号:U1431227)资助。

摘　　要：天体测量定标是高精度位置测量的基础.空间望远镜图像的天体测量定标是我国计划于2024年发射的空间站工程巡天望远镜需要突破的关键技术.本文以“卡西尼”(Cassini)飞行器窄视场照相机(Narrow Angle Camera,NAC)拍摄的图像为例,探究了CCD图像天体测量定标技术,希望为拓展应用到我国即将发射的空间站工程巡天望远镜提供有益的参考.具体地,本文选取了NAC在五个历元(2006,2008,2010,2014,2016)拍摄的具有不同指向和取向观测密集星场的图像,探究了空间图像高精度天体测量的归算方法,求解出了各历元的CCD扭曲模型.相比目前其他学者的归算结果,本文在恒星的位置测量精度上有较大的提高.对于在2.6 s曝光时间11–12星等(GaiaG星等)的恒星,平均(O-C)(The Observed Minus Computed)的标准差在x和y坐标方向分别约为0.04像素(约提高0.5倍)和0.03像素(约提高1倍).通过分析各历元图像的扭曲模型,本文发现在飞行器执行任务期间CCD图像的扭曲保持了良好的稳定性.在1024×1024像素尺度下,几何扭曲的最大值、中值、最小值分别为0.184±0.023,0.038±0.005和0.007±0.003像素.根据求解扭曲的平均模型,本文提供了模型的数值表达式及改正方法.The astrometric calibration of images taken from the China Space Station Telescope(CSST)is the key technique for preparing the CSST,which should start scientific operations around 2024.Taking the astrometric calibration of Cassini ISS images as an example,we hope to provide a reference for the images taken from the CSST.Observations of Cassini narrow angle camera with different orientations and pointings at dense star fields over five epochs(epochs 2006,2008,2010,2014,and 2016)are used to perform astrometric reduction and to derive accurate geometric distortion models.For each frame,the star image centroids from the modified moment method are matched with the newest Gaia DR3 catalog and calculated to their topocentric apparent positions.Then,we reduce the observations using a fitted weighted fourthorder polynomial plate model and correct the effect of the charge transfer efficiency(CTE)issues(if they exist).To derive the geometric distortion model at each epoch,a weighted four-parameter plate model is used to calculate and derive the(O-C)s(the observed minus computed)of stars.We calculate the median of the(O-C)s in each area of a divided 8×8 box in the pixel coordinate after considering the effect of CTE.Finally,we fit the geometric distortion model at each epoch.Compared with the reduction results of Zhang et al.(2021),our results show a considerably improved precision of the stars.For brighter stars(e.g.,11-12 mag with an exposure time of 2.6 s),the standard deviations of the mean(O-C)are~0.04 and~0.03 pixels(approximately a 0.5-and 1.0-fold improvement,respectively)on the x-and y-axes,respectively.The geometric distortion models are stable over the five epochs.In the 1024×1024 pixel image,the maximum,median,and minimum of the geometric distortion values are 0.184±0.023,0.038±0.005,and 0.007±0.003 pixels,respectively,which differ from Owen's model in 2003.The mean geometric distortion model,as well as the correction method,is given in this work.

关 键 词：空间望远镜 视场定标 CCD图像处理 天体测量 几何扭曲 

分 类 号：P111[天文地球—天文学]