Methodology for in-flight flat-field calibration of the Lyman-alpha solar telescope(LST)

摘要

Flat-field reflects the non-uniformity of the photometric response at the focal plane of an instrument,which uses digital image sensors,such as Charge Coupled Device(CCD)and Complementary Metal-Oxide-Semiconductor(CMOS).This non-uniformity must be corrected before being used for scientific research.In this paper,we assess various candidate methods via simulation using available data so as to figure the in-flight flat-field calibration methodology for the Lyman-alpha Solar Telescope(LST).LST is one of the payloads for the Advanced Space-based Solar Observatory(ASO-S)mission and consists of three instruments:a White-light Solar Telescope(WST),a Solar Disk Imager(SDI)and a dual-waveband Solar Corona Imager(SCI).In our simulations,data fromthe Helioseismic andMagnetic Imager(HMI)and Atmospheric Imaging Assembly(AIA)onboard the Solar Dynamics Observatory(SDO)mission are used.Our results show that the normal KLL method is appropriate for in-flight flat-field calibration of WST and implementing a transmissive diffuser is applicable for SCI.For the in-flight flat-field calibration of SDI,we recommend the KLL method with off-pointing images with defocused resolution of around 18′′,and use the local correlation tracking(LCT)algorithm instead of limb-fitting to determine the relative displacements between different images.