平场数据采集间隔对莱曼阿尔法太阳望远镜平场精度的影响分析

莱曼阿尔法太阳望远镜(LST)是先进天基太阳天文台(ASO-S)卫星的载荷之一,它包括白光太阳望远镜(WST),全日面太阳成像仪(SDI)和日冕仪(SCI)等仪器. 1991年Kuhn, Lin和Loranz提出的方法(简称KLL方法)是WST和SDI在轨平场定标的方法之一.为了研究WST和SDI的平场定标精度对KLL方法的相邻位置时间间隔的敏感性,使用太阳动力学观测卫星(SDO)的日震和磁成像仪(HMI)及太阳大气成像仪(AIA)的全日面成像观测数据测试和分析在使用KLL方法时相邻位置时间间隔对所得平场精度的影响.结果显示在LST使用KLL方法进行平场定标时,相邻位置时间间隔越短越好.具体分析表明,WST平场精度对相邻位置采样时间间隔不敏感,而SDI时间间隔需要在240 s范围内.分析结果对卫星姿态调整到稳定所需的时间给出了一定限制.

Influence of the Flat Field Data Acquisition Interval on the Lyman-alpha Solar Telescope Flat Field Accuracy

The Lyman-alpha Solar Telescope (LST) is one of the payloads for the Advanced Space-based Solar Observatory (ASO-S) mission, and it consists of a White light Solar Telescope (WST), a Solar Disk Imager (SDI), and a Solar Corona Imager (SCI). And one method of its in-flight flat field calibration is the so-called KLL method proposed by Kuhn, Lin, and Loranz in 1991. In order to study the influence of KLL method''s time interval between two successive offset positions on the derived flat fields of the WST and SDI instruments, we use the full-disk images from the Helioseismic and Magnetic imager (HMI) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) satellites to mimic the images of WST and SDI observations, and use them as test images for the KLL method calculation. Based on our calculation and analysis, we got the following conclusions: when we adopt the KLL method to obtain the flat feild, the shorter the time interval, the better the flat field accuracy. This puts some requirements for the spacecraft platform. Considering the time required for the satellite''s attitude adjustment and stabilization as well as image acquisition, the time interval for SDI flat field needs to be within 240seconds. The WST flat field accuracy is not sensitive to the time interval between two successive offset positions. This conclusion also limits the time required for the satellite''s attitude adjustment and stabilization.