日冕区太阳风对深空电波传播影响的研究

发布时间：2018-05-25 01:47

本文选题：上合期间 + 深空通信　；参考：《哈尔滨工业大学》2017年博士论文

【摘要】：作为传输探测信息的唯一载体,深空通信是人类开展深空探测活动的重要手段。连接深空探测器和地球观测站间的无线电波在上合期间会穿过太阳日冕区,该区域高浓度、强不规则性的太阳风湍涡等离子体会引起无线电波的衰减和链路通信质量的下降,甚至引发通信中断,进而对深空探测的正常开展造成严重的影响。因此,构建可靠的深空通信网是未来深空探测的重要保障,而如何准确计算日冕区太阳风对无线电波的影响已成为深空通信中亟需解决的问题。目前,对这一课题的研究主要集中于以下两方面,一方面,考虑日径距离(太阳到无线链路的垂直距离)大于4Rsun时,背景太阳风对沿直线传播的无线电波的吸收预测模型。另一方面,考虑各向同性湍涡媒质折射指数变化所引起的电波信号随机起伏变化,给出幅度起伏、相位起伏和到达角起伏的预测模型。然而,随深空探测活动的增多,日冕区太阳风对日径距离小于4Rsun时的电波吸收和各向异性湍涡下太阳闪烁的影响变得更为严重,并已成为制约未来深空通信发展的技术瓶颈。如何准确预测日冕区太阳风对深空无线电波的影响将成为深空通信发展的关键。因此,无论是对4Rsun内电波衰减的预测,还是对各向异性湍涡下太阳闪烁的预测都是深空通信的基础性和前瞻性课题,并已成为深空电波传播领域的热点研究问题。本文以日冕区背景太阳风和随机起伏太阳风对电波传播影响为目标,针对已有工作不足之处,以随机媒质中电波传播理论为出发点,探索日冕区太阳风对电波吸收的准确预测模型,在考虑太阳风湍涡各向异性特点的基础上,进一步研究太阳闪烁对无线电波幅度、相位和到达角起伏的影响,并系统阐述日冕区太阳风对电波传播的影响机理,从而为未来深空探测中上合期间深空通信的正常开展提供研究思路。论文首先建立了日冕区链路方向电子含量变化模型,在此基础上,具体分析日冕区太阳风对穿过其中无线电波相位、传播时间、信号频率和极化特性的影响,并研究近日点处太阳风等离子体薄层对无线电波的反射率、透射率和吸收率。针对日径距离小于4Rsun时,背景太阳风对电波吸收的影响,论文提出一种考虑太阳磁场变化的相对介电常数计算方法,并分别给出无线电波在左极化和右极化模式下的修正衰减预测模型,最后,结合WKB近似理论分析提出预测模型与传统模型的对比结果,此外利用提出的衰减预测模型,论文进一步给出不同日径距离下的电波衰减值。考虑弱太阳闪烁下太阳风湍涡不规则性对无线电波幅度起伏的影响,论文分析了上合期间链路几何模型和湍涡媒质起伏特性。在此基础上,依据“泰勒冻结理论”将太阳风湍涡假设成缓慢变化的随机媒质,并利用Rytov近似理论给出幅度起伏预测模型和弱太阳闪烁下的闪烁指数预测模型。研究发现,日冕区背景参数对幅度起伏有较为复杂的影响,且闪烁指数随日径距离的减小而增大。考虑到太阳风湍涡受太阳磁场影响具有各向异性的特点并随日径距离的增大趋于各向同性,论文进一步分析了各向异性和各向同性模型下的闪烁指数性能。研究结果表明,提出的闪烁指数预测模型与实测数据较为吻合,且其预测精度远大于其他预测模型。针对上合期间无线电波受太阳闪烁影响所产生的相位起伏问题,论文系统地分析了上合期间链路几何模型及太阳风湍涡谱特性,并研究了太阳风速度、湍涡外尺度和湍涡谱指数对相位起伏的影响,利用几何光学法论文给出了相位起伏的预测模型,以及相位起伏方差和相位起伏功率谱的计算模型。此后,论文重点讨论了日冕区背景参数对相位起伏的影响及各参数的综合影响。与实测数据的对比结果表明,提出预测模型具有较高的预测精度。考虑在较大日径距离范围时太阳风湍涡具有各向同性的特点,论文基于Rytov近似理论和各向同性的湍涡谱模型推导了各向同性模型下的到达角起伏预测模型。为评估天线口径平滑效应的影响,提出模型将Airy函数替换为高斯函数,并进一步推导到达角起伏的功率谱模型。针对无线电波穿过各向异性日冕区湍涡的情形,论文从工程角度分析了到达角起伏与相位起伏的关系,并利用几何光学法下的相位起伏模型推导给出到达角起伏预测模型。在此过程中,论文通过Booker电子密度谱考虑了各向异性太阳风湍涡的影响。利用上述推导得到的到达角起伏预测模型,论文分析了日冕区背景参数对到达角起伏的影响,并对比分析两种预测模型的预测精度。在此基础上,论文进一步分析了无线电波工作频率和天线口径对链路增益的影响。
[Abstract]:As the only carrier for transmission detection information, deep space communication is an important means for human to carry out deep space exploration activities. The radio waves connecting deep space detectors and earth observation stations will pass through the solar coronal area during the up period. The high concentration, strong irregularity of the solar wind eddy plasma experience causes the attenuation and chain of radio waves in this region. The decline of the quality of the road communication, even the interruption of communication, has a serious effect on the normal development of deep space exploration. Therefore, the construction of a reliable deep space communication network is an important guarantee for the future deep space detection, and how to accurately calculate the influence of the solar wind on the radio waves in the corona area has become an urgent problem in the deep space communication. The research on this subject is mainly focused on the following two aspects. On the one hand, considering the absorption prediction model of the background solar wind to the radio waves propagating along the straight line when the diurnal distance (the vertical distance of the sun to the wireless link) is greater than 4Rsun. On the other hand, the wave signal caused by the refraction index changes of the isotropic turbulent medium is taken into account. The prediction model of amplitude fluctuation, phase fluctuation and arrival angle fluctuation is given. However, with the increase of deep space exploration activity, the solar wind in the coronal region has more serious influence on the wave absorption and the anisotropy under the anisotropic turbulent vortex, which has become a technical bottleneck for the development of the future deep space communication. How to accurately predict the influence of solar wind in coronal region on deep space radio waves will be the key to the development of deep space communications. Therefore, both the prediction of the attenuation in the 4Rsun and the prediction of the solar scintillation under the anisotropic eddy are both basic and forward-looking topics in the deep space communication, and have become a hot spot in the field of deep space radio transmission. In this paper, this paper aims at the influence of the solar wind and random fluctuating solar wind on the wave propagation in coronal region. In view of the shortcomings of the existing work, the accurate prediction model of the solar wind absorption in the coronal region is explored, based on the theory of the wave propagation in the random medium, and the anisotropy of the solar wind eddy is considered. The influence of the solar scintillation on the amplitude, phase and arrival angle fluctuation of the radio wave is further studied, and the influence mechanism of the solar wind on the wave propagation in the coronal region is systematically expounded, so as to provide the research ideas for the normal development of the deep space communication during the sounding of the deep space in the future. On this basis, the influence of solar wind on the phase, propagation time, signal frequency and polarization characteristics of the radio waves through the coronal region is analyzed, and the reflectance, transmittance and absorption of the solar wind plasma thin layer at the perihelion are studied. The background solar wind is absorbed by the solar wind when the solar wind is less than 4Rsun. The paper presents a method for calculating the relative dielectric constant of the solar magnetic field, and gives the modified Attenuation Prediction Model of the radio waves in the left and right polarization modes. Finally, the comparison results of the prediction model with the traditional model are presented with the WKB approximation theory. In addition, the proposed Attenuation Prediction model is used. This paper further gives the attenuation values of the radio waves under different diurnal distances. Considering the influence of the irregularity of the solar wind vortex under the weak solar scintillation on the amplitude fluctuation of the radio waves, the paper analyses the geometric model of the link and the undulating characteristics of the turbulent eddy medium during the up period. On this basis, the solar wind eddy is assumed to be slow on the basis of the "Taylor freezing theory". The amplitude fluctuation prediction model and the scintillation index prediction model under the weak sun flicker are given by the Rytov approximation theory. It is found that the background parameters of the coronal region have a more complex effect on the amplitude fluctuation, and the scintillation index increases with the decrease of the diurnal distance. It has anisotropic characteristics and tends to isotropy with the increase of diurnal distance. The paper further analyzes the performance of the scintillation index under anisotropic and isotropic model. The results show that the proposed model is more consistent with the measured data, and its prediction precision is far greater than that of other prediction models. The problem of phase fluctuation caused by the solar scintillation is caused by the linear wave. This paper systematically analyzes the geometric model of the link and the spectral characteristics of the solar wind turbulence, and studies the influence of the solar wind velocity, the outer scale of the turbulent vortex and the spectral index of the turbulence on the phase fluctuation, and the prediction model of the phase fluctuation is given by the geometrical optics method. The calculation model of the phase fluctuation variance and phase fluctuation power spectrum. After that, the paper focuses on the influence of the coronal background parameters on the phase fluctuation and the comprehensive influence of the parameters. The comparison with the measured data shows that the prediction model has a higher prediction accuracy. Based on the Rytov approximation theory and the isotropic turbulent eddy spectrum model, the paper derives the prediction model of the arrival angle fluctuation under the isotropic model. In order to evaluate the effect of the antenna aperture smoothing, the model is put forward to replace the Airy function as Gauss's function, and to further deduce the power spectrum model of the angular fluctuation. The relationship between the arrival angle fluctuation and the phase fluctuation is analyzed from the engineering angle, and the prediction model of the arrival angle fluctuation is derived from the phase fluctuation model under the geometric optics method. In this process, the paper considers the shadow of the anisotropic solar wind eddy through the Booker electron density spectrum. In this paper, the influence of the background parameters on the arrival angle fluctuation of the coronal region is analyzed and the prediction accuracy of the two prediction models is analyzed. On this basis, the influence of the frequency of radio wave and the aperture of the antenna to the link gain is further analyzed.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：V443.1;P353.8

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