火星电离层无线电掩星探测仿真研究

对中俄联合火星星-星电离层掩星技术体制进行了分析和介绍,采用三维射线追踪方法对电离层掩星事件的电波观测值进行了模拟计算,并利用模拟的掩星观测数据进行了电子密度廓线反演,结果说明仿真算法可靠.利用仿真的方法,分别对掩星电波相位观测误差和卫星轨道误差等带来的反演误差进行了个例计算和分析,结果得到:5%周的相位测量误差对白天电离层掩星探测结果的影响可以忽略,而夜间电子密度测量的绝对误差小于4×108 m-3;卫星轨道误差对掩星的主要影响是导致电离层高度抬升或下降.结果表明,中俄联合火星电离层掩星探测技术体制先进,可望获得高精度的电子密度廓线;其技术体制也可以用于月球电离层环境的探测.     

基于特征向量算法的Loran—C天波延迟估计的研究

提出了一种基于特征向量算法来估计Loran-C接收机天波延迟的信号处理新技术,为设计具有自适应调节最佳采样点的Loran-C接收机打下良好的基础.建立了基于频谱相除技术的信号模型,简要介绍了特征向量的谱估计算法.研究了此算法估计天波延迟的准确性,并与IFFT技术作了对比.仿真结果显示.特征向量算法比IFFT具有更高的分辨率和尖锐的波峰.最后,通过实测数据的实验验证了这些结论.     

德令哈13.7m望远镜重力变形研究

借助于数字摄影测量结果调整天线面板,使德令哈13.7 m望远镜在仰角52°时获得最佳反射面面形,从而使天线效率在观测仰角范围内得到整体优化.与之前基于经纬仪测量的面板调整结果相比,天线口径效率提高约1倍.依据不同俯仰姿态下的测量结果,得到了天线的重力变形模型,包括副面偏移和倾斜、主面焦距和面形偏差随仰角变化的规律.根据不同仰角的面形偏差测量数据反演反射面重力变形模型时,采用了数据拟合方法,这样可以减小测量误差对模型精度的影响.     

星地无线电双向时间比对模型及试验分析

星地时间同步是卫星导航系统的一个关键技术,是实现卫星导航定位的基础.针对星地时间同步问题,讨论了一种星地无线电双向时间比对方法,详细推导了该方法中星地上下行伪距的归算模型,给出了星地钟差的实用计算模型.该方法通过上下行伪距求差,消除了对流层延迟、卫星星历误差和地面站站址坐标误差等共有误差影响,与信号频率有关的电离层延迟也被很大程度地削弱,从而大大提高了时间比对精度.最后,利用实测数据进行了试验分析,结果表明:星地无线电双向时间比对精度能够达到约0.34ns,验证了理论方法和模型的正确性.     

GALILEO搜救定位处理的分布式数据融合方法

对遇险目标搜索救援的支持是GALILEO全球卫星导航系统的一项重要民用服务.文章介绍了GALILEO搜索救援子系统(SAR)定位的基本原理.在GALILEO SAR中测量量为时间信号与频率信号,文章详细地给出了两种测量信号的定位方法.基于多传感器信息融合技术,对搜索救援系统中不同测量信号进行综合状态估计.在仿真计算中,采用带噪声的模拟测量数据进行定位,数值计算的结果显示基于多传感器数据融合方法的综合状态估计是可靠的.     

电离层延时对低轨卫星频率传递的影响分析

利用低轨卫星,对受干扰区域的卫星导航接收机进行频率传递,是提升其性能的一种有效手段.而电离层延时误差是影响传递效果的重要因素.对基于低轨卫星的频率传递应用背景进行了介绍,分析了其基本原理,并着重分析了电离层延时的存在对频率传递的影响,提出利用站间差历元差的方法对电离层延时进行修正.最后,通过仿真对理论分析进行了验证.结果表明,通过站间差历元差的手段,对当前电离层变化值进行求解与预测,可以将电离层延时误差的变化控制在一定范围,满足频率传递的要求.     

类水星系外行星偏振特性研究

通过对不可分辨水星偏振相位曲线的研究了解类水星不可分辨系外行星的偏振特性,为用偏振探测手段寻找类水星系外行星提供有力的依据.通过贝叶斯非线性拟合得到水星测光相位曲线和偏振相位曲线,进而得到不可分辨水星的偏振相位曲线.从该曲线中得出以下结果: (1)水星在不可分辨情况下在可见光波段其偏振度的量级为10-12;(2)垂直于散射平面和平行于散射平面的最大偏振度相当,且它们所对应的相位角相对于可分辨情况下发生了明显的改变;(3)在相位角大于158°时不可分辨水星的偏振度几乎为零.     

电离层掩星反演的正则最大熵法

电离层掩星数据现已成为电离层观测数据的重要来源,对掩星数据的反演研究一直是掩星研究的热点.传统采用的改正TEC(1btal Electron Content)的Abel变换反演法为线性反演法,它会把测量误差带入反演结果中.为改善反演效果受测量误差的影响,引入两种非线性的反演方法一正则化和正则最大熵反演法.随后设计模拟试验,对3种方法进行验证、比较,得到正则最大熵反演法可以很好地减小测量误差的影响.     

65 m射电望远镜背架结构日照温度效应实验研究

借助精密工程测量手段,对65 m天线背架的日照温度效应进行了实验研究.在天线背架没计坐标系下分析实验数据,建立了日照温度变形模型,得出背架结构沿X方向变形系数为K_X=1.30×10^-5,沿Z方向变形系数为K_Z=-0.44×10^-5,沿Y方向变形偏向太阳照射一侧.根据实验数据建立的背架变形模型,模拟分析了65 m天线背架日照温度变形对面形精度的影响,得出环境温度变化1℃带来的面形精度（均方根值rms）影响分量约为0.09 mm.实验结果为65 m天线主动面调节提供了很有价值的参考数据.     

基于数字摄影测量技术的13.7m毫米波天线面形检测

将工业数字摄影测量技术首次应用于13.7 m毫米波射电望远镜天线的面形精度检测中.为克服现场条件的限制,在测量中使用环形轨道输送相机,采用无线传输的方式进行现场摄影.采用回光材料制作人工的标志,利用编码标志完成摄站的自动定向和同名点匹配,用光束法平差的方法解算点的3D坐标.利用CAD面形转换法和自由拟合法计算面形偏差,最终480个调整点的面形CAD拟合后的偏差调整到了0.083 mm.验证了摄影测量在射电天文天线测量中的可行性和优越性.     

Observation and Research of the Transits of Extrasolar Planets

In order to make more accurate estimates of the physical parameters of extrasolar planets, the observation and research on the phenomena of transits of the 7 known stars with the planetary systems TrES-1, TrES-3, XO-2, WASP-1, WASP-2, WASP-3 and HAT-P-7 are carried out with the 1-m reflecting telescope at Shandong University Weihai Astronomical Observatory/Weihai Municipal Astronomical Observatory. The fundamental conditions of the observation and data processing are introduced, and the transit light curves as well as the parameters of some planets derived from them are given. At the same time, when the results are summarized and analyzed, the prospects for the more in-depth and detailed researches which will be further carried out are also described.     

基于CSST多色测光的时序测光精度分析

中国巡天空间望远镜(Chinese Survey Space Telescope, CSST)是中国的首个大型空间光学望远镜, 将对包括系外行星探测在内的诸多科学目标开展研究, 有望取得前沿科学进展. 时序测光精度是CSST重要的性能指标, 受到物理噪声和仪器噪声的影响, 需要通过数值模拟对其分析和评估. 模拟基于目前公布的CSST主要技术参数, 建立了时序的恒星信号和噪声模型, 以CSST的i波段为例, 分析凝视观测模式下的测光精度. 通过数值仿真, 展示了孔径测光中各项噪声的贡献, 特别是由指向抖动和像素响应不均匀性导致的抖动噪声. 模拟结果还给出了测光孔径的推荐范围. 为了获得更高的信噪比, 可以减小仪器抖动振幅和像素不均匀性, 或者采用参考星较差测光的方式. 结果为CSST后续的时序测光精度与不同指标参数的相关性分析、系外行星探测能力评估以及测光数据处理提供了模拟数据的支撑.     

Virial treatment of the speed of sound in cold, dense atmospheres and application to Titan

The speed of sound in a gas can be used to identify its composition, as has been done on the Earth. We show that, unlike in terrestrial applications, the third virial coefficient cannot be neglected in cold and dense atmospheres. We derive a model for the speed of sound of pure gases and gas mixtures at low temperatures and high pressures, based on the virial equation. After comparing the results of our model to measured data, we apply our model to the atmosphere of Titan. The difference between our third-order virial expansion and the commonly used second-order expansion is significant, showing that the third virial coefficient needs to be taken into account when accurate speed-of-sound measurements are used to derive atmospheric properties under Titan conditions.     

天语计划——寻找第二个太阳系及探索动态宇宙

像木星和土星这样的冷巨行星对类地行星的形成和宜居性起到了关键作用, 因此, 对像太阳系这样具有多个冷巨行星的系统的搜寻具有重要意义. Kepler以及TESS (Transiting Exoplanet Survey Satellite)太空望远镜成功地通过凌星的方法发现了大量短周期行星, 然而这些巡天项目的观测基线不足以发现更长周期的行星. 为此, 天语计划将部署两台1m望远镜(天语一号和天语二号),用于结合天语和其他计划的数据通过凌星法来发现冷巨行星及其他行星, 并最终发现类太阳系. 天语一号具有约10平方度的视场以及高速CMOS (complementary metal-oxide-semiconductor)科学相机, 将对超过1000万颗恒星每小时进行一次高精度测光采样, 并通过天语二号的多波段测光、光谱仪以及高分辨率成像对天语一号发现的候选行星进行确认. 天语望远镜将放置于海拔约4000m的中国青海冷湖, 是目前中国境内最好观测台址之一. 天语对亮于14等星的测光精度为0.1%, 对亮于18等星的测光精度优于1%, 天语预计在5yr内将在类太阳周期发现超过300颗凌星行星,其中包括约17颗冷巨行星. 基于系统轨道共面以及孪生地球发生率为10%的假设, 天语预计将发现1--2个类太阳系, 并可被未来的地球2.0计划所证实. 此外,天语还将通过多种巡天观测模式测量从亚秒到周时标的光变, 探测不同时标的时域现象, 包括超新星早期光变、稀有变星和双星、潮汐瓦解事件、Be星、彗星活动以及系外小行星等.这些发现不仅将深化我们对宇宙的理解, 还将为公众科学和科普提供重要平台.     

A Research on the Imaging Strategy and Imaging Simulation of Toutatis in the Chang’e-2 Flyby Mission

For the Chang’e-2 extended mission of asteroid exploration, the illumination conditions for imaging the asteroid Toutatis are calculated in this paper according to the orbital parameters of both the Chang’e-2 detector and the asteroid, as well as the incident angles of sunlight. On this basis, it is suggested to take photographs after flyby, and the orientation of the camera's optical axis in the coordinate system deflned by Earth's mean equator and equinox at J2000.0 is proposed to be (118.02°, 22.03°). Based on the shape model of Toutatis determined by the foreign radar data, the orientation of the asteroid in the inertial space is calculated at the rendezvous time. Using the Oren-Nayar diffuse-reflection model and the relative positions among the sun, the asteroid, and the detector, together with the cameras orientation, the imaging simulations are performed on the starry sky background respectively at the distances of 300 km, 500 km, and 1000 km from the asteroid after flyby. The results of simulations are verified further by the optical images of Toutatis obtained in the mission.     

Transit timing effects due to an exomoon – II

In our previous paper, we evaluated the transit duration variation (TDV) effect for a co-aligned planet-moon system at an orbital inclination of   i = 90°  . Here, we will consider the effect for the more general case of   i ≤ 90°  and an exomoon inclined from the planet-star plane by Euler rotation angles  α, β  and γ. We find that the TDV signal has two major components, one due to the velocity variation effect described in our first paper and one new component due to transit impact parameter variation. By evaluating the dominant terms, we find the two effects are additive for prograde exomoon orbits, and deductive for retrograde orbits. This asymmetry could allow for future determination of the orbital sense of motion. We re-evaluate the ratio of TDV and transit timing variation effects, η, in the more general case of an inclined planetary orbit with a circular orbiting moon and find that it is still possible to directly determine the moon's orbital separation from just the ratio of the two amplitudes, as first proposed in our previous paper.     

Transit timing effects due to an exomoon

As the number of known exoplanets continues to grow, the question as to whether such bodies harbour satellite systems has become one of increasing interest. In this paper, we explore the transit timing effects that should be detectable due to an exomoon and predict a new observable. We first consider transit time variation (TTV), where we update the model to include the effects of orbital eccentricity. We draw two key conclusions.

• (i) 

  In order to maintain Hill stability, the orbital frequency of the exomoon will always be higher than the sampling frequency. Therefore, the period of the exomoon cannot be reliably determined from TTV, only a set of harmonic frequencies.
• (ii) 

  The TTV amplitude is  ∝ M _S a _S  where M _S is the exomoon mass and a _S is the semimajor axis of the moon's orbit. Therefore, M _S and a _S cannot be separately determined.

We go on to predict a new observable due to exomoons – transit duration variation (TDV). We derive the TDV amplitude and conclude that its amplitude is not only detectable, but the TDV signal will also provide two robust advantages.

• (i) 

  The TDV amplitude is  ∝ M _S a ^−1/2_S  and therefore the ratio of TDV to TTV allows for M _S and a _S to be separately determined.
• (ii) 

  TDV has a π/2 phase difference to the TTV signal, making it an excellent complementary technique.