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先进多孔径视宁度廓线仪(A-MASP)由两台小望远镜组成,通过望远镜观测太阳表面的米粒结构进行日间湍流廓线测量.两台望远镜之间的相对指向误差可以通过改进的湍流廓线测量公式消除.数值仿真研究表明,使用消除抖动的湍流廓线计算公式后,发现A-MASP对地表附近的湍流不敏感.当两台望远镜距离为0.4 m时,无法测量400 m以下的湍流.在A-MASP中,采样高度的不均匀分布会造成测量结果的失真,可通过等效采样高度的计算方法,对该失真进行修正.通过100层相位屏对大气湍流的仿真,结果表明当望远镜距离不同时,湍流廓线测量的结果各有侧重.当距离较近时(0.4 m),A-MASP对0.4–5 km的湍流廓线测量精度较高.当距离为1.2 m和2.0 m时,对5 km以上的湍流廓线测量较准确. 相似文献
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射电天文信号非常微弱,电磁环境对射电望远镜观测至关重要,通常可以利用地形、建立无线电宁静区、进行电磁屏蔽与防护等手段来减小电磁干扰.然而,仍有一些干扰难以屏蔽.故提出了一种基于自适应滤波的干扰消除方法,可用于复杂噪声环境中天文信号的提取.该方法借助自适应横向滤波器,采用最小均方(Least Mean Square, LMS)误差算法,以系统误差和收敛性为评判标准,通过改变步长与阶数对滤波效果进行优化,仿真结果显示该滤波器能在保证算法收敛的前提下有效提取信号.为了检验该算法的有效性,选取了新疆天文台南山26 m射电望远镜和Parkes 64 m射电望远镜记录的观测数据,采用设计的滤波器分别对不同的实测数据进行测试,验证了该滤波器的有效性.理论分析与实验结果一致表明该方法能有效消除天文观测中的干扰信号,具有一定的实用性. 相似文献
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多径效应对接收机环路影响的仿真研究 总被引：1，自引：0，他引：1
为了研究和减小卫星导航接收机中的多径误差的影响,从理论上对多径效应引起的码相位和载波相位误差进行了分析,完成了Matlab下相应的仿真,为进一步消除多径误差奠定了基础. 相似文献
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GIM在LEO卫星单频GPS定轨中的应用 总被引：1，自引：0，他引：1
电离层延迟误差是单频GPS(Global Positioning System)数据最主要的误差源,为提高基于单频GPS数据的LEO(Low Earth Orbiting)卫星定轨精度,必须消除/减弱GPS观测数据中电离层延迟影响.研究了全球电离层模型GIM(Global IonosphericMaps)在基于单频GPS伪距数据的低轨卫星运动学和动力学定轨中的应用,并通过估算电离层尺度因子的方法消除C/A码伪距观测量中电离层延迟影响.由于LEO卫星星载GPS信号受电离层延迟影响与卫星轨道高度相关,选取了轨道高度在300～800 km的CHAMP(CHAllenging Mini-satellite Payload)、GRACE(Gravity Recovery AndClimate Experiment)、TerraSAR-X及SAC-C等LEO卫星C/A码伪距观测量作为试算数据.CHAMP等卫星实测数据计算结果表明:以JPL(Jet Propulsion Laboratory)发布的GIM模型作为背景模型,通过电离层比例因子法能很好地消除C/A码伪距观测量中电离层延迟影响,提高LEO卫星运动学和动力学定轨精度,其中,CHAMP卫星轨道最低,受电离层延迟影响最严重,定轨精度提高最显著,分别为55.6%和47.6%;SAC-C卫星轨道高度最高,受电离层延迟影响最小,相应的定轨精度提高幅度也最低,分别为47.8%和38.2%. 相似文献
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嫦娥一号卫星搭载的干涉成像光谱仪(Interference Imaging Spectrometer, IIM)用于获得月表元素的含量. IIM光谱左右色调不均一, 影响元素制图精度, 因此有必要对其进行平场校正, 消除探测器各像元的光谱响应不一致对图像产生的影响. 在嫦娥一号卫星在轨运行1 yr期间(2007年10月至2008年10月), 干涉成像光谱仪共获得576轨数据, 之前已有学者进行过平场校正, 但是校正结果不能适用于月表所有地区. 结合了2008年11月和12月获得的130轨数据, 采用基于光谱特征的反射率归一化方法, 通过选取大量太阳矢量与卫星轨道面夹角beta对称的轨道中的均一平坦、无曝光过度地区的光谱数据, 对其平均求得平均行, 利用平均行求得校正因子实现平场校正. 对比校正前后光谱图像和反射率曲线, 月球不同地形的色调不均一现象和条纹均得到有效的消除, 这将有利于后续元素的反演和实际应用. 相似文献
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卡西尼号探测器携带了光学成像科学子系统(ISS: Imaging Science Subsystem), 在2004--2017年间拍摄了一些土星内卫星的图像. 部分图像中土星内卫星非常靠近土星环, 观测对象受土星环散射光影响导致测量精度差, 甚至无法测量. 由此提出一种适用于这类图像的背景消除算法, 可对受土星光环散射光影响的土星内卫星进行测量. 归算了7颗近环内卫星(土卫十(Janus)、土卫十一(Epimetheus)、土卫十五(Atlas)、土卫十六(Prometheus)、土卫十七(Pandora)、土卫三十二(Methone)和土卫四十九(Anthe))的70张ISS图像, 并与不消除散射光的方法进行了比较. 结果显示, 该方法至少可以提高43%的精度. 和喷气推进实验室的土星卫星历表\lk SAT415相比, 测量得到的赤经和赤纬方向的残差均值分别为0.72km和2.26km, 标准差分别为10.99km和11.36km. 相似文献
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《天文研究与技术》2017,(3)
射电天文观测数据受无线电的影响日益严重。因此,射频干扰(Radio Frequency Interference,RFI)消除已经成为信号处理流程中不可或缺的一步。考虑了自适应阵列信号处理中的移动干扰源的消除问题,对于阵列天线望远镜而言,射频干扰消除可以通过采样协方差矩阵在空域实施处理。在很多应用场景中,可得到的零点深度受限于协方差矩阵的估计误差,进而影响干扰子空间的估计精度。方法应用了一种多项式模型以跟踪阵列协方差矩阵随时间的变化,消除干扰子空间的估计误差,提高干扰消除性能。最后通过仿真对比了传统的子空间投影(Subspace Projection,SP)算法和基于多项式模型的子空间投影(Polynomialaugmented Subspace Projection,PSP)算法,仿真结果证明了所提方法的有效性。 相似文献
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Ⅱ型光电等高仪 总被引：1，自引：0，他引：1
我国于1972年制成Ⅰ型光电等高仪,1974年又制成Ⅱ型光电等高仪.新仪器的特点如下:(1)借助熔石英角镜组和汞地平、一架望远镜和固定的玻璃记录栅、三个光电倍增管及其交流放大器和一架计时仪,此仪器能无人差地测定星过等高圈时刻.(2)真空的 R-C 望远镜的口径为20厘米,焦距2.4米.(3)有水平入射窗的真空镜筒能消除天文折射、大气色散及镜筒内的反常折射.真空镜筒还为光学系统及汞面提供了一个稳定的环境.(4)此仪器设有快、慢传动电机和自动方位跟踪机构.(5)为消除周围物体的热影响,此仪器安放在观测室楼上,而控制台、电器设备和操作者都在楼下.自1974年10月起,此仪器已在上海天文台进行了常规观测.获得的优良观测结果将在以后发表. 相似文献
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A technique to detect man-made interference in the visibility data of the Mauritius Radio Telescope (MRT) has been developed.
This technique is based on the understanding that the interference is generally ‘spiky’ in nature and has Fourier components
beyond the maximum frequency which can arise from the radio sky and can therefore be identified. We take the sum of magnitudes
of visibilities on all the baselines measured at a given time to improve detectability. This is then high-pass filtered to
get a time series from which the contribution of the sky is removed. Interference is detected in the high-pass data using
an iterative scheme. In each iteration, interference with amplitudes beyond a certain threshold is detected. These points
are then removed from the original time series and the resulting data are high-pass filtered and the process repeated. We
have also studied the statistics of the strength, numbers, time of occurrence and duration of the interference at the MRT.
The statistics indicate that most often the interference excision can be carried out while post-integrating the visibilities
by giving a zero weight to the interference points. 相似文献
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Yang Ting-gao Tong Ming-lei Zhao Cheng-shi Gao Yu-ping 《Chinese Astronomy and Astrophysics》2019,43(1):93-100
The X-ray timing data for the Crab pulsar obtained by the Chinese X-ray pulsar navigation test satellite are processed and analyzed. The method to build the integrated and standard X-ray pulse profiles of the Crab pulsar by using the X-ray pulsar observation data and the satellite orbit data is described. The principle and algorithm for determining the pulsar's pulse time of arrival (toa) in the frequency domain are briefly introduced. The pulsar's pulse time of arrival is calculated by using the timing data of 50 min integration for each set of observational data. By the comparison between the observed Crab pulsar's pulse time of arrival at the solar system barycenter and that predicted with the Crab pulsar ephemeris, it is found that the timing accuracy is about 14 μs after the systematic error is removed by a quadratic polynomial fitting. 相似文献
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The Gegenschein is viewed by the Solar Mass Ejection Imager (SMEI), which has provided near-full-sky broadband visible-light photometric maps for over 5 years. These have an angular resolution of about 0.5° and differential photometric stability of about 1% throughout this time. When individual bright stars are removed from the maps and an empirical sidereal background subtracted, the residue is dominated by the zodiacal light. The unprecedented sky coverage and duration of these measurements enables a definitive characterization of the Gegenschein. This article describes the analysis method for these data, presents a movie with time of the Gegenschein brightness distribution, determines empirical formulae describing its average shape, and discusses its variation with time. These measurements unambiguously confirm previous reports that the Gegenschein surface-brightness distribution has a decided peak in the antisolar point, which rises above a broader background. 相似文献
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Zsolt Kővári Katalin Oláh János Bartus Klaus G. Strassmeier Thomas Granzer 《Astrophysics and Space Science》2006,304(1-4):55-57
The photometric light modulation of ζ Andromedae originates from the distorted geometry of the primary, and additionally, from spots of which parameters (temperature, size, location) are variable in time. We present spot modelling results for six two-colour light curves which show that spots preferably appear on the stellar surface towards the companion star and opposite to it, where the distortion also causes dimming. Therefore, simple fitting of the measured data for the ellipticity effect does not yield correct result. Instead, ellipticity calculated from exact stellar parameters should be removed from the data to get reliable spotted light curves. 相似文献
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The gravity field of Venus has been modeled by a spherical harmonic expansion of the potential to degree and order seven. The estimates of these coefficients were obtained by combining information from 43 short arcs (4 hr) of line-of-sight Doppler data centered at periapsis. The data arcs were distributed in longitude and time over more than two circulations of Venus by the Pioneer Venus Orbiter subperiapsis point which was confined to the band of latitudes from 14°N to 17°N. Convergence of the solution has been assured by iterating upon the initial estimate. All estimates were performed with zero a priori information on the gravity coefficients. Since the altitude of periapsis for most of the orbits was within the sensible Venusian atmosphere, drag effects on the estimated harmonics have been removed using an exponential atmosphere density model. Estimates of the mass parameter (GM) of Venus using this dataset are also evaluated. 相似文献
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Haraldur Pll Gunnlaugsson 《Planetary and Space Science》2000,48(15):1491-1504
The paper presents the results of a new analysis of the data from the Magnetic Properties Experiment onboard the Mars Pathfinder Spacecraft. The spectral data from the extended visible region of material adhering to the magnets are presented as well as the time dependence of dust accumulation to the magnets. A new model is developed to estimate the magnetic properties of the accumulated dust. It is found that the optical reflection spectra of the magnetic dust differ slightly from the reflection of ground soil/dust in the vicinity of the lander. Several possible hypotheses are given to account for this difference. Magnetic dust has been removed from the magnets at least twice during the 80 sol mission by wind gusts, and it is suggested that this happens in a manner similar to sand blasting. A lower limit for the saturation magnetisation of the most magnetic particles is found to be 5 Am2/kg. 相似文献
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A fractal analysis using the classical Hurst method has been applied to artificial data, simulated sunspot magnetic field data, and to data acquired with NASA/Marshall Space Flight Center's vector magnetograph. The main goals of this study are to quantify the complexity of an active region and to determine if significant changes in complexity are associated with flare activity. We tested the analysis using three basic types of two-dimensional synthetic data: (1) data composed of gaussians with various types of superimposed features, (2) random data, and (3) synthetic sunspots created from a basic, simple configuration on which are placed increasingly smaller structures. Our results confirm that the Hurst method of analysis is sensitive to the presence of large-scale structures within a two-dimensional image. When the large-scale structure has been removed, the value of the Hurst exponent is inversely proportional to increasing complexity in the image. The Hurst exponent of magnetograph data with the large-scale structure of the sunspot removed, shows a tantalizing variation in the shear parameter five minutes prior to a flare. 相似文献
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H. Baumgardt † 《Monthly notices of the Royal Astronomical Society》2001,325(4):1323-1331
We report results of collisional N -body simulations aimed at studying the N dependence of the dynamical evolution of star clusters. Our clusters consist of equal-mass stars and are in virial equilibrium. Clusters moving in external tidal fields and clusters limited by a cut-off radius are simulated. Our main focus is to study the dependence of the lifetimes of the clusters on the number of cluster stars and the chosen escape condition.
We find that star clusters in external tidal fields exhibit a scaling problem in the sense that their lifetimes do not scale with the relaxation time. Isolated clusters show a similar problem if stars are removed only after their distance to the cluster centre exceeds a certain cut-off radius. If stars are removed immediately after their energy exceeds the energy necessary for escape, the scaling problem disappears.
We show that some stars that gain the energy necessary for escape are scattered to lower energies before they can leave the cluster. As the efficiency of this process decreases with increasing particle number, it causes the lifetimes not to scale with the relaxation time. Analytic formulae are derived for the scaling of the lifetimes in the different cases. 相似文献
We find that star clusters in external tidal fields exhibit a scaling problem in the sense that their lifetimes do not scale with the relaxation time. Isolated clusters show a similar problem if stars are removed only after their distance to the cluster centre exceeds a certain cut-off radius. If stars are removed immediately after their energy exceeds the energy necessary for escape, the scaling problem disappears.
We show that some stars that gain the energy necessary for escape are scattered to lower energies before they can leave the cluster. As the efficiency of this process decreases with increasing particle number, it causes the lifetimes not to scale with the relaxation time. Analytic formulae are derived for the scaling of the lifetimes in the different cases. 相似文献
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A mixture of periodic and chaotic components makes the detection of chaos difficult. The periodic components are sought in the solar UV time series by the Maximum Entropy Method and are removed by a digital notch filter. The filtered output is subjected to investigation for chaotic behavior by three different techniques. (1) Fixed-size method for attractor dimension determination; (2) sensitive initial dependence via prediction error; (3) trajectory direction estimation. All the investigation points to the existence of a chaotic attractor of fractional dimension. 相似文献