远紫外光学遥感载荷在轨定标技术研究进展

Research Progress on On-Orbit Calibration Technology for Far Ultraviolet Payload

远紫外波段(115~200 nm)光学遥感是在卫星上获得空间环境参数,如O,N 2和O 2等中性大气原子分子柱密度及廓线分布、电离层电子密度TEC、电子密度廓线、等离子体含量、大气温度廓线、太阳EUV流量、能量粒子沉降等信息的重要探测技术,也是最具发展潜力的空间天气探测方法之一。定量获得这些物理参量的重要过程之一是载荷的辐射定标,包括发射前实验室定标和在轨定标。发射前定标给出载荷的原始定标系数,而在轨定标则给出仪器在轨运行一段时间后定标系数的变化。远紫外探测技术用于中高层大气、电离层、磁层、太阳活动等方面的研究从19世纪70年代就已经开始,以美国为代表的一些国家已将远紫外探测列入空间天气监测的长期规划,并且开展了大量的在轨定标技术研究,确保载荷数据的长期定量化应用。我国在本世纪初才开展远紫外波段载荷技术的研究,在轨定标技术基本属于空白。在轨定标方法包括基于外部标准辐射源定标、基于内部辐射标准源定标和替代定标三种。以国际上具有代表性的远紫外探测载荷为例,分析和总结这三种定标方法分别用于成像探测、光谱成像探测和光度计三种主要的探测类型仪器上的定标方案、在轨定标数据处理方法及处理结果。对多种类型载荷及不同定标源定标方法及结果分析表明,对于视场较大,且具备深空观测能力的远紫外波段成像仪器及成像光谱仪,首选外定标源法,即采用远紫外辐射相当稳定且已知光辐射强度的的紫外恒星作为辐射标准源,根据运行轨道进行定标模式合理设计,并结合实验室定标数据,实现在轨全视场定标;对于光度计类的单点探测仪器,由于视场限制,极少有恒星观测条件,故推荐采用替代定标方式,实现载荷在轨长期监测,但在定标数据的选取及时空匹配方面应详细分析,以提高定标精度;而利用内部标准源进行定标的方法,标准源本身的衰减问题是亟待解决的问题。

Far Ultraviolet wavelengths(FUV 115 to 200 nm)optical remote sensing detection on satellite is one of the most promising technologies on space weather.This technology can be effectively used to obtain some important space environment parameters,such as O,N 2,O 2 column density and profile distribution,total electron content(TEC)of ionosphere and electron density profile.It also yields valuable information on content of plasma,temperature profile of the atmosphere,solar EUV flux and energy particle.In the processes of obtaining these physical parameters quantitatively there is one key step—the radiation calibration,including pre-launch laboratory calibration and on-orbit calibration:the former gives original calibration coefficient of the load before launch;the latter checks the change of the calibration coefficient of the instrument’s on-orbit performance after a set period.In the West,FUV technology application to upper atmosphere,ionosphere,magnetosphere and solar activity started in the 1970s,and has been applied to the long-term Space Weather Program Strategic Plan by U.S.federal government.In China,this technology was carried out at the beginning of the 21 st century,and the in-flight calibration is still a research gap now.This paper introduces on-orbit calibration technologies for some representative far ultraviolet payload based on the external standard radiation source,internal radiation standard source and vicarious calibration,and then analyses the data processing method and the results on three kinds of FUV remote sensing:Imager,Spectrometer Imager and Photometer.The results suggest that the best on-orbit calibration method for imager or spectrometer imager is using UV stellar as an external radiation standard;the instrument can catch the known radiation from the stellar;using the radiation from the stellar and the spectral responsibility from the lab,the sensitivity of the instrument will be known as in-flight.The internal standard radiation source,like deuterium lamp,is not a good choice for in-flight calibration becauseradiation itself from lamp attenuates.On single-point detection instrument,like a photometer with limited visual field,the vicarious calibration is a good way to realize on-orbit calibration.During the process of calibration,data selecting and spatio-temporal matching should be cautiously conducted in order to enhance the calibration accuracy.