地基红外太阳观测的背景辐射特性研究

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	地基红外太阳观测的背景辐射特性研究
其他题名	Research on background radiation characteristics of ground-based infrared solar observation
	赵志军
学位类型	博士
导师	刘忠
	2018
学位授予单位	中国科学院大学
学位授予地点	北京
学位专业	天文技术与方法
关键词	大气红外消光和辐射大气红外辐射涨落仪器红外辐射多元定标模型整机制冷
摘要	随着太阳物理的进一步发展，对红外太阳观测提出了更高分辨率（空间分辨率、时间分辨率、光谱分辨率）和更宽光谱范围（往长波红外发展）的要求，国内外纷纷建造大口径光学红外太阳望远镜。然而，如何更有效的发挥这些大口径望远镜在红外波段的观测性能，是当前不得不面对的现实问题。望远镜自身红外辐射的大小和台址大气红外消光、红外辐射及其涨落的强弱直接关系到大口径望远镜能否发挥其灵敏度优势。这就要求我们对地基红外太阳观测的背景辐射特性进行研究，一方面，研究红外仪器自发辐射的变化规律和可能的抑制方法；另一方面，实测不同地区的大气红外消光、红外辐射及其涨落，从中选出优秀的红外台址来放置大口径红外太阳望远镜。本论文从地基红外太阳观测需求出发，分析了地球大气对太阳红外辐射传输的影响，阐述了测量大气红外辐射和消光的必要性；对仪器的红外辐射特性和大气红外辐射特性及其实测方法进行了深入研究，仿真分析了仪器的红外辐射特性，基于此，研制了一台工作在3~5um波段低红外发射的辐射测量设备；对影响地基红外太阳观测的大气吸收、大气背景辐射及其涨落等大气辐射传输特性参数进行了实测，基于实测结果，分析了大气辐射和消光的时空变化特性及其对红外天文观测的影响。（1）通过Lowtran7大气辐射传输模型研究了地球大气对太阳红外辐射传输的影响，对大气消光（透过率）随海拔的变化规律进行了仿真，研究了不同气体分子对消光的贡献，海拔对消光的影响；然后，对太阳红外辐射在大气中的传输进行了仿真，讨论了被地球大气吸收后的日面及日冕红外辐射和地球大气红外辐射的强弱对比关系，指出测量大气红外辐射和消光对大口径红外太阳望远镜选址和地基红外太阳观测的必要性。（2）研制了一台用于大气辐射和消光特性测量的整机制冷设备，利用光学仿真软件Tracepro对仪器的红外辐射进行了仿真，分析了仪器辐射的变化规律，通过设计消光螺纹，仪器辐射降为1/5，当制冷到-40摄氏度时，仪器辐射可以降为常温（20摄氏度）的1/20；为了测量相对弱的大气红外辐射的涨落，考虑将仪器进行制冷；通过LBLRTM大气辐射传输模型对M'波段的大气辐射亮度进行计算，将计算结果表示成等效黑体温度，在Tracepro中对像面接收到的大气等效黑体辐射和光机结构的红外辐射进行了仿真，结果表明，在-40摄氏度时仪器辐射是大气辐射的23.6%，综合考虑光机系统的工作温度范围，将仪器制冷到-40摄氏度，控温精度±0.03摄氏度；设计了一套冷却水循环加两级半导体的三级制冷系统，对测量仪器进行整机制冷；设计了一套整机性能测试方法，测量所得单像元时噪声等效温差（NETD）为26.5mK，通过全靶面平均，系统NETD可以降为4.5mK，设备可用于大气红外辐射及其涨落的测量。（3）为了解决辐射测量一元定标方法动态范围不足的问题，提出了允许探测器曝光时间改变的二元定标模型；通过高低温实验，研究了二元模型随温度的变化规律，发现二元模型表征仪器辐射的系数随环境温度的变化符合Planck函数规律；基于此，提出引入环境温度作为第三个自变量的三元定标模型测量法，通过外场实验验证了三元模型用于大气辐射测量的有效性。实验数据表明，三元模型与实测数据拟合程度很高，相关系数为1.000，均方根误差（RMSE）为4.25个数字读数（adu）；模型参数a、b、d，95%置信度的相对不确定度均小于0.82%。三元模型定标测量法使用条件宽泛，既扩大了仪器动态范围，又不受环境温度变化影响；更重要的是，可省去现场定标，提高了测量精度和测试效率。（4）利用所提的三元定标模型对四个台址的大气红外辐射亮度进行了高精度测量，测量结果的精度优于4.4%，并比较了不同台址的昼夜大气红外辐射的差异；基于大气红外辐射传输方程和Kirchhoff定律，提出了一种通过测量不同天顶角大气辐射亮度来反演大气消光的方法，并通过LBLRTM辐射传输模型仿真验证了所提方法的可行性；将天顶角扫描观测方法用于大气辐射和消光空间变化的实测，结果表明，测量所在地，大气辐射从正天顶到60°天顶角增加了67%，大气透过率则降低了33%，大气辐射和消光的变化将严重影响地基红外观测。（5）对四个站点大气辐射的时间涨落进行了测量，并对比了测量结果；通过Allan方差法对采集到的大气辐射和黑体辐射的时间涨落进行分析，二者的Allan方差曲线表明在低频部分大气辐射的涨落远强于黑体的；给出了白天和夜间，不同台址Allan方差曲线对比，结果表明，不同台址之间Allan方差的差异可达3个数量级，同一台址昼夜之间Allan方差相差2~3个数量级，Allan方差曲线随时间变化规律也有差异，Allan方差结果可用于对红外台址进行评价；研究了观测视场内大气辐射涨落在空间上的相关性，结果表明视场内的辐射涨落是高度相关的；利用Allan方差法分析了大气辐射涨落对红外天文观测的斩波频率的影响，结果表明不同台址的最佳斩波频率有比较大的差异，最佳斩波频率越小则越适合红外太阳观测。本文测量与研究大气红外背景辐射所提出的测量仪器整机制冷方法、多元定标方法、天顶角扫描测大气消光的方法及大气辐射时间涨落的Allan方差分析法等对于大口径红外太阳望远镜选址及未来红外望远镜设计和观测模式选择都有重要的指导意义。
其他摘要	With the further development of solar physics, put forward higher resolution (spatial resolution, time resolution, spectral resolution) and broader spectral range (long wave infrared) solar telescope, many large ground-based optical and infrared solar telescopes was built nowadays in the world. Nevertheless, a practical problem is how to maximize the sensitivity of ground-based large infrared solar telescope, because the sensitivity of large infrared solar telescope is limited by the thermal radiation from the telescope and atmospheric infrared extinction and the fluctuation of atmospheric infrared radiation at the astronomy site. This will require us to research background radiation characteristics of ground-based infrared solar observation. On the one hand, researching the infrared radiation characteristics of the instrument; on the other hand, measuring atmospheric infrared extinction and atmospheric infrared radiation and radiation fluctuation of different sites, then finding excellent sites to place large aperture infrared solar telescopes.In this paper, based on the demand of ground-based infrared solar observation, the influence of the earth atmosphere on the solar infrared radiation is analyzed, and the necessity of measuring the infrared radiation and extinction of the atmosphere is expounded; conducts in-depth study on property of instrument and atmospheric infrared radiation and transmission and its measurement methods, the infrared radiation characteristic of instrument was simulated and an infrared radiation measuring equipment with low emissivity can work in 3~5um waveband was developed based on simulation results. Parameters of atmospheric infrared radiation and transmission influenced ground-based infrared solar observations, such as atmospheric absorption, atmospheric background radiation, atmospheric radiation fluctuations were measured.(1) The influence of earth atmosphere of solar infrared radiative transfer is studied with Lowtran7 atmospheric radiative model, the atmospheric extinction (transmittance) changes with altitude is simulated, the different contributions of gas molecules to extinction and effects of altitude on extinction are studied; and then, the characteristics of solar radiative transfer in the earth atmosphere are simulated, the relationship between transmitted solar infrared radiation through the atmosphere and infrared radiation of the earth's atmosphere are discussed, pointed out that the measurement of atmospheric infrared radiation and extinction on the site survey of large aperture infrared solar telescope and the ground-based infrared solar observation is necessary.(2) A refrigeration equipment for the measurement of atmospheric radiation and extinction characteristics has been developed, infrared radiation of instruments was simulated with Optical simulation software named Tracepro and changes rules of instrument radiation was analyzed, results show that extinction threads make instrument radiation down to 1/5 and radiation of instrument at -40 degrees Celsius is down to 1/20 of 20 degrees Celsius instrument. Because the fluctuation of atmospheric infrared radiation is faint target, considering the instrument for refrigeration; M' waveband radiance was calculated by LBLRTM and represented as temperature of equivalent blackbody, taking temperature of blackbody as target, then the infrared radiation of target and opto-mechanical structure of instrument at image surface was simulated by Tracepro, results show that the infrared radiation of -40 degrees Celsius instrument is 23.6% of atmospheric infrared radiation. Considering operating temperature of opto-mechanical system,the refrigeration temperature of instrument was set to -40 degrees Celsius and temperature control accuracy was ±0.03 degrees Celsius; three stages refrigeration system with one stage cooling water circulation and two stages semiconductor was developed for cooling the whole instrument. A method used in the performance test of entire instrument was designed, according to the results of test, noise equivalent temperature difference (NETD) is 26.5mK for single pixel, NETD of instrument can reduce to 4.5mK based on the average of all pixels, the instrument can be used for the measurement of atmospheric radiation and its fluctuation.(3) In order to solve the problem of deficient dynamic range of single variate calibration method for radiometric measurements, bivariate calibration model which allows to change exposure time was proposed; the temperature dependence of bivariate calibration model was investigated in high and low temperature controlled experiments, data of the temperature dependence of infrared radiation of the instrument fit well with Planck function. Thus trivariate calibration model was presented and tested in outfield experiments, results show that R-square is 1.000, root mean square error (RMSE) is 4.25 adu and the relevant uncertainties in 95% confidence degree of a, b and d, parameters of the trivariate calibration model, are all less than 0.82%. The benefit of this trivariate calibration model is that it can extend the dynamic response of the measuring instruments, and the precision of its measurement result is not affected by the variation of ambient temperature. Hence this model can be widely used and can achieve high-precision measurement result without in-situ calibration.(4) Atmospheric infrared radiance of four sites was measured precisely with trivariate calibration model, the precision is better than 4.4%, then difference of atmospheric radiation in four sites during both day and night; a method for measurement of atmospheric extinction by measuring atmospheric radiation with varying zenith angle was presented based on atmospheric infrared radiative transfer equation and Kirchhoff law, then the method was tested by the LBLRTM simulation; Spatial variation characteristics atmospheric radiation and extinction was measured through the method of radiation measurement with varying zenith angle, results show that atmospheric radiation increased by 67%, atmospheric transmittance decreased by 33% from zenith to 60° zenith angle at experimental location, ground-based observation will be seriously influenced by the variation of atmospheric radiation and extinction.(5) Time series of atmospheric infrared radiance of four sites were measured, measurement results were compared; Fluctuation characteristics of atmospheric and blackbody radiation were analyzed with Allan variance method, fluctuations of atmospheric radiation are much larger than fluctuations of blackbody in low frequency region according to Allan variance curve; Allan variance curves of four sites during both day and night were showed, results show that difference of 3 orders of magnitude between the Allan variances of four sites, difference of 2~3 orders of magnitude between day and night in the same site, the influences of time-dependent Allan variance change are different in different sites, Allan variance can be used to evaluate infrared site; Spatial correlation of atmospheric radiation fluctuations between different field of view of sky was researched, radiation fluctuations are strongly correlated in field of view; the effect of the radiation fluctuation on the chopping frequency of infrared astronomical observations was analyzed with Allan variance, results show that the best chopping frequency of different sites is quite different, the smaller the best chopping frequency is, the more suitable for infrared solar observation..The refrigeration method, multivariate calibration method, a method for measurement of atmospheric extinction by measuring atmospheric radiation with varying zenith angle and atmospheric radiation time fluctuation analysis with the Allan variance method proposed in this paper are significant for the site survey, design of large infrared solar telescopes and observational mode of telescopes.
学科领域	天文学
学科门类	理学 ; 理学::天文学
页数	95
语种	中文
文献类型	学位论文
条目标识符	http://ir.ynao.ac.cn/handle/114a53/25374
专题	天文技术实验室
作者单位	中国科学院云南天文台
第一作者单位	中国科学院云南天文台
推荐引用方式 GB/T 7714	赵志军. 地基红外太阳观测的背景辐射特性研究[D]. 北京. 中国科学院大学,2018.

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