基于O2(0-1)谱带反演气辉层转动温度的研究

Inversion of Rotational Temperature in Airglow Layer Based on O2(0-1) Atmospheric Band Spectrum

中间层与低热层区域(mesosphere and lower thermosphere,MLT)处于中性大气与电离层大气之间的过渡区域,也是中高层大气中一个重要的耦合区域。基于自主研发的中间层顶气辉光谱光度计(mesopause airglow spectral photometer,MASP),对其探测转动温度的反演方法进行了详细研究。MASP的整个探测系统包括光阑、消色差双胶合透镜、窄带干涉滤光片、镜头、制冷CCD探测器,元件之间通过黑色氧化铝套筒连接,利用金属支架和精密的卡环将套筒和CCD探测器固定在面包板上。外壳具有良好的隔热性能,并配有低功率半导体TEC空调,保证恒温在(23±0.5)℃。MASP的视场角为±13.6°,探测高度为94 km左右,观测视角投影在该高度上的天顶方向的区域直径约为44 km,探测目标为该区域内厚度约为3~6 km气辉层的平均温度。基于仪器的光学原理、气辉O 2(0-1)带的光谱特征以及标定后各项仪器参数,构建了正演模型,并从正演图像中计算出了合成光谱。给出了反演算法的详细流程,包括暗噪声、宇宙射线、月光图像和连续光谱背景杂散光的剔除方法,同时提供了实际观测合成光谱的计算方法,温度反演流程及其误差的评估。2018年9月开始在南京信息工程大学观测场平台进行连续观测,目前已经获得多组高质量的数据。文中的观测实例展示了2次完整夜间的观测个例,以及2018年10月间13组有效数据的平均值,其整体变化趋势显示观测温度分布在170~220 K之间,误差范围在±1.8~±4.3 K之间。通过与MSISE00经验模型的数据进行对比,温度趋势具有良好的一致性,从而验证了反演方法的有效性和准确性。MASP结构紧凑,性能稳定,后期易于维护,适用于多台站组网观测。

The Mesosphere and Lower Thermosphere(MLT)is a transitional region between the neutral atmosphere and the ionosphere,as well as an important coupling region where many dynamic processes including gravity waves,tidal waves and planetary waves are active.Based on the Mesopause Airglow Spectral Photometer(MASP),a novel instrument developed by our group,this work provides the inversion method in detail for deriving rotational temperature from the emission of the airglow O 2(0-1)band.MASP instrument consists of an aperture,a main achromatic doublet lens,a narrow-band interference filter,an imaging lens and a cooled CCD detector.The optical elements and CCD detector are connected by four black alumina sleeves which are fixed on the optical breadboard by means of several metal supports and precise clasps.The field of view(FOV)for MASP is±13.6°,and the detection target is a thin airglow layer at an altitude of about 94 km with a thickness of 3~6 km.Thus,the area of the zenith direction projected by the FOV at this altitude is about 44 km in diameter so that MASP is designed to detect the average temperature of this area.Based on the optical principle of MASP,the spectral characteristics of the airglow O 2(0-1)band and the instrument parameters by calibrations,we constructed the forward model to calculate synthetic spectrum from the forward image.We then describe the detailed process of the inversion algorithm,including the eliminations of dark noise,cosmic rays,moonlight images and background scattered signal of the continuous spectrum.In addition,the calculation method of the actual observed synthetic spectrum,the temperature inversion process and the evaluation of the error are provided respectively.The MASP has been conducting routine observations on the field platform of Nanjing University of Information Engineering since September 2018.At present,more than thirty nights of data have been obtained.The observation results in this paper show two whole night observation cases and the mean value averaged by 13 sets of valid data in October 2018.The general trend shows that the observed temperature ranges from 170 to 220 K,and the error ranges from(+1.8 K)to(+4.3 K).Compared with the data of the MSISE-00 empirical model,the temperature trend has a good consistency,which verifies the validity and accuracy of the inversion method.MASP has compact structure,stable performance and easy maintenance.It is thereforesuitable for multi-station networking observation.