共查询到20条相似文献，搜索用时 31 毫秒
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The forecasting technique of the target tracking based on the short arcs at single station is an important way to guarantee that high-precision photoelectric theodolites can normally track and capture the targets in unconventional environments. We construct the tracking prediction algorithm based on nonlinear filter, which can provide the guiding data for the closed loop tracking under normal circumstances. At the same time we also construct the target prediction algorithm based on the nonlinear transformation, without valid observational data, which can provide a track guidance for the theodolite and ensure that the targets will not be lost. It is demonstrated that the nonlinear filtering is more effective than the EKF (extended Kalman filter) in the tracking prediction algorithm of the short arcs at single station. The results indicate that the nonlinear filter designed in this paper can be used as the guiding algorithm for the optical tracking equipments. And its guiding accuracy is in the same order of magnitude of the theodolite's random measurement accuracy. When the systematic error of the equipments reaches 50″, the accuracy can achieve 20″ for predictions in 60 s. This still satisfies the requirement of the field of view of the tracking equipments. 相似文献
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An Improved Grey Model and Its Application Research on the Prediction of Real-time GPS Satellite Clock Errors 总被引：2，自引：0，他引：2
In the work on the real-time GPS precise point positioning, the realtime and reliable prediction of the satellite clock error is one of the keys to the realization of the GPS real-time high accuracy point positioning. The satelliteborne GPS atomic clock has high frequency, is very sensitive and extremely easy to be influenced by the outside world and its own factors. Therefore, it is very difficult for one to know well its complicated and detailed law of change, with these attributes being in accordance with the characteristics of the theory of grey system. Thus, it is considered that the process of variation of the clock error is regarded as a grey system. On the basis of the exploration of the limitations of the quadratic polynomial and grey model satellite clock error predictions, the research on the real-time prediction of the GPS satellite clock error by taking advantage of the improved grey model is proposed. Finally, the materials of the GPS satellite clock error of 3 different time intervals are used to make the accuracy analysis of the clock error prediction of different sampling intervals, to study the relation between the grey model exponential coefficient and the prediction accuracy and to make the analysis of the comparison of the prediction accuracy with that of the quadratic polynomial method. The general relation between the different types of satellite clock errors and the model exponential coefficients is summarized and compared with the IGS final clock error ephemeris product to test and verify the feasibility and availability of the improved prediction model proposed in the present article so as to provide the higher-accuracy satellite clock error products for the real-time GPS dynamic precise point positioning. 相似文献
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The meteor radar response function is an important tool for analyzing meteor backscatter observed by radar systems. We extend previous work on the development of the response function to include a non-uniform meteor ionization profile, provided by meteor ablation theory, in contrast to what has been assumed in the past. This has the advantage that the height distribution of meteors expected to be observed by a radar meteor system may be accurately modeled. Such modeling leads to meteor height distributions that have implications for the composition of those meteoroids ablating at high altitudes which may be observed by “non-traditional” meteor radars operating at MF/HF. The response function is then employed to investigate meteor backscatter observed by narrow beam MST radars which in recent years have been used increasingly to observe meteors. 相似文献
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A technique of cross-correlation for the determination of stellar positions is proposed. It is a technique suitable for the recording of stellar positions on transit instruments, photoelectric astrolabes, and also on the meridian circles with reversed observing method. An advantage of this process is that there is no hypothesis required for the modelling image profile, and for the noise. It is closer to unbiased estimation. Results by this new method on a transit instrument are presented. For the brighter stars, there is no great difference in accuracy between the median position and the cross-correlation value according to the results. 相似文献
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We develop a theory for radar signal scattering by anisotropic Langmuir turbulence in the solar corona due to a t+l ⇄ t process. Langmuir turbulence is assumed to be generated within a cone by a narrow type III burst electron beam. Using wave-kinetic
theory we obtain expressions for the frequency shift, scattering cross-section of the turbulence, coefficient of absorption
(due to scattering) and optical depth. On the basis of those expressions we give some estimates for an echo spectrum. We show
that the minimum radar echo frequency shift is determined by the minimal phase velocity of the Langmuir waves, the maximum
shift is determined by the electron beam velocity, but in any case it can not exceed −wt/2 (decay) and wt (coalescence), where
wt is the frequency of a radar signal. The angular characteristics of the scattered signal differ dramatically for the cases
of coalescence and decay. The signal is scattered into a narrow cone high above the specular reflection point (wp ≪ wt), but
in the vicinity of wp ∼ wt/2 the red-shifted echo is scattered isotropically, while the blue-shifted echo is scattered into
a even narrower cone. We show that absorption (due to scattering) increases with increasing radar frequency. The dependence
of the absorption on the local plasma frequency is strongly determined by the Langmuir turbulence spectrum. Our theory shows
that the role of the nonlinear scattering process t+l ⇄ t is essential and that such process can be used for radar studies of the spectral energy density of anisotropic Langmuir turbulence. 相似文献
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Numerical methods are usually used for the computation of ephemerides with perturbations for the precise orbital determination of an artificial satellite. But their numerical stability will be encountered in a long arc. In this case the use the improved Encke special perturbation methods has been suggested. The results of this paper show that Encke's method does indeed have a certain effectiveness, but cannot yet completely resolve the numerical stability, and the more efficient method is to use the energy integral or its variational relation to control the growth of the along-track error in general numerical calculations so that the aim of stabilization can be achieved. 相似文献
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北美防空司令部(North American Aerospace Defense Command, NORAD)发布的双行根数(Two Line Element, TLE)是广大航天工作者最常用的轨道根数,与其对应的轨道模型是SGP4/SDP4 (Simplified General Perturbation Version 4/Simplified Deep-space Perturbation Version 4)解析模型.由于TLE中并没有包含相应的轨道精度信息,编目轨道的应用范围受到很大的限制.基于Space-Track网站发布的历史TLE数据和配套的SGP4/SDP4动力学模型,采用定轨标预报的方法统计并生成了大量目标轨道的预报误差,通过对预报轨道的时间区间划分给出了每个目标的预报误差随预报时间变化的拟合系数,并进一步对不同类型轨道预报误差的演化规律和特征进行了分类讨论,给出了4种轨道类型目标的轨道预报误差随时间演化的平均解析模型,为拓展双行根数的应用提供有价值的参考. 相似文献
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即将用于新疆奇台110 m射电望远镜(Qi Tai radio Telescope,QTT)的促动器需在-40~60℃范围内满足±15μm的精度要求。由于在无任何补偿的情况下,热误差可以达到约400μm,因此需要建立热误差模型,以预测促动器位移随温度的变化规律,并在此基础上进行位移主动控制补偿,从而保证促动器在给定温度下能满足定位精度的要求。首先,结合模型基本要求与显著性检验,从促动器上的16个温度测量点中优选出一个最适合模型建立的点;然后,采用灰色预测理论建立促动器的热误差模型;最后,根据实际情况对该模型进行修正。研究表明:创新地采用统计学与工程实践相结合的方式选取测温点,建立的热误差模型可以指导促动器的位移主动控制补偿,从而使促动器在要求的-40~60℃范围内达到±15μm±4μm的定位精度。 相似文献
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本文介绍了预报水(金)星凌日的计算方法和凌日图的绘制方法,建立了一套完整的预报程序。作为该程序的一个简单应用,我们结合DE200历表及美国海军天文台提供的岁差章动程序,给出了1999年水星凌日的预报结果。 相似文献
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C. Burigana P. Natoli N. Vittorio N. Mandolesi M. Bersanelli 《Experimental Astronomy》2001,12(2):87-106
In-flight measurements of the shape of the antenna main beam is a crucial input to the data analysis pipeline of each high
resolution Cosmic Microwave Background (CMB) anisotropy experiment. We study the main beam reconstruction achievable by the
PLANCK Low Frequency Instrument (LFI) through the observation of external planets. Although were strict our analysis to the
30 GHz LFI channel, the method can be easily extended to all the PLANCK frequency channels and to other CMB anisotropy experiments.
We show that it is possible to fit the time ordered data from the external planets (mainly Jupiter and Saturn) to obtain an
accurate, robust, simple and fast reconstruction of the main beam properties under very general conditions, almost independently
of the calibration accuracy. In addition, we find that a bivariate Gaussian approximation of main beam shapes represents a
significant improvement with respect to asymmetric representation. The impact of the most relevant systematic effects is also
addressed. We demonstrate that by combining the recovery of the maximum signal at the planet transit with accurate in-flight
calibration, it is possible to measure the intrinsic planet temperatures at millimetric wavelengths with < 1% accuracy. This
work is based on PLANCK-LFI activities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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The order of magnitude of the error is investigated for a first-order von Zeipel theory of satellite orbits in an axisymmetric force field, i.e., first-order long period and short-period effects are included along with second order secular rates. The treatment is valid for zero eccentricity and/or inclination. In the case where initial position and velocity vectors are known, the in-track position error over time intervals of order 1/J
2 is kept at 0(J
2
2), like the other position errors and velocity errors, by calibration of the mean motion with the aid of the energy integral. The results are specifically applicable to accuracy comparisons of the Brouwer orbit prediction method with numerical integration. A modified calibration is presented for the general asymmetric force field which includes tesseral harmonics. 相似文献
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针对目前流星雷达测距误差大的问题，本文提出了提高流星雷达测距精度的新方法，即提高采样速率，用相关分析确定回波脉冲参考点的方法。该方法使流星雷达的测距精度提高一个数量级，测距误差降到±１４ｍ，使流星雷达不仅可以用来观测研究流星，还可用于监测飞机、火箭的飞行等，扩大流星雷达的应用。 相似文献
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We discuss a new method for measuring the coordinates of meteor shower radiants from meteor radar data. The method uses a high accuracy of radar goniometer measurements of one of the angular coordinates for meteor radiants and collective properties of incident meteor showers. It is based on a computer technology of searching for the coordinates of radiants using the intersections of meteor position lines on the celestial sphere and filtering nonrandom combinations of these intersections. The method allows the following: to detect meteor showers with a rate of more than 5 per day of observations and to separate meteor groups from different meteor showers with different radiants and velocities. The method makes it possible to increase the angular resolution from 10° × 10° achieved with a quasi-tomographic technique to 2° × 2°, with a prospect of a further increase in the accuracy through the individual reduction of separated meteor groups. We use the reduction of one-day-long observations during maximum activity of the Geminids meteor shower in 1993 to illustrate the potentialities of the method. We show an example of detecting a weak meteor shower that was active during December 1993. 相似文献
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The Jicamarca Radio Observatory (JRO) two-dimensional square array radar system operating at ~ 6-m wavelength was used to study the Moon and low Earth orbit satellites using the Range-Doppler inverse synthetic aperture radar technique also known as Delay-Doppler imaging. The radar data was collected on Oct 21, 2015. A circularly polarized coded pulse was transmitted from a quarter-array antenna segment during lunar transit over JRO. Dual-linear polarization receive systems were employed on two quarter-array segments and on two 1/64th array modules giving the longest possible baselines across the transit path. A Range-Doppler mapping technique that uses the rotational motion of the targets and an autofocusing motion and ionospheric delay compensation technique has been implemented to generate the two-dimensional maps of the point-target (Satellite) and range-spread target (Moon). A review of our technique and the maps obtained from these observations is presented herein. Range-Doppler maps of the Moon and satellites are instructive with regards to possible further improvement of the technique, especially regarding ionospheric compensation. 相似文献
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中高轨卫星广播星历精度分析 总被引：17，自引：0，他引：17
GPS广播星历参数具有物理意义明确、参数少、精度高等优点,可以考虑将它应用于其他卫星导航系统。但是GPS系统的卫星构成比较单一,而其他卫星导航系统可能包含中地球轨道 (MEO)、倾斜地球同步轨道(IGSO)和地球静止轨道(GEO)等多种不同类型的中高轨卫星。分析了采用GPS广播星历参数时,MEO、IGSO和GEO卫星的广播星历拟合精度,特别讨论了轨道倾角接近于0的GEO卫星的广播星历拟合精度,并给出了相应的改进措施。计算表明,对于 MEO卫星,2 h的广播星历拟合精度(三维位置)可达厘米级;对于IGSO卫星和轨道倾角较大的GEO卫星,4 h的广播星历拟合精度约为0．1 m,径向位置误差在厘米量级;而对于轨道倾角接近于0的GEO卫星,若不采取特殊措施,由于轨道倾角和升交点经度统计相关,其广播星历拟合精度很差,为此提出了一种坐标转换方法。采用此方法后的广播星历拟合精度可达0．1 m,径向位置误差为厘米量级。 相似文献
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MEI Geng-jun XIANG Bin-bin WANG Na WANG Zhao-jun 《Chinese Astronomy and Astrophysics》2021,45(2):236-251
The pointing accuracy of a radio telescope is usually less than one-tenth of its antenna beam width. For large-aperture antennas at the short-centimeter band or millimeter-wave band, the pointing accuracy must be as high as several arc seconds. Therefore, for large-diameter and high-frequency reflector antennas, the pointing problem has become an important focal point to realize the antenna performance. Among many structural subsystem factors that affect the antenna pointing accuracy, there has been only less study on the factor of main reflector deformation. Based on the structural characteristics of the antenna, a reflector space coordinate system is established in this paper. And based on the space coordinates of the main reflector surface points after deformation, a non-linear least squares fitting method with 3 degrees of freedom is proposed to accurately predict the antenna pointing. Finally, the space geometric relationship is used to strictly derive the precise adjustments on the elevation and azimuth in order for correcting the antenna pointing error, and the indirect relationship between the main reflector deformation and the pointing error is constructed. This has certain guiding significance for improving the pointing accuracy of large radio antennas. 相似文献
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连线干涉测量(Connected Element Interferometry, CEI)是一种全天时全天候的被动测角技术, 已用于空间目标的跟踪监视. 地球静止轨道(Geostationary Earth Orbit, GEO)卫星需要频繁机动以保持轨位或完成其他任务, 其机动后的快速轨道恢复能力对于监视预警极为重要. 针对基于CEI的GEO短弧定轨和预报, 分析了定轨算法的形亏和数亏, 在附加先验轨道约束的短弧定轨基础上, 提出了轨道半长轴初值的自适应优化方法. 利用亚太七号卫星的CEI仿真和实测数据进行了短弧定轨和预报, 实验结果表明, 采用优化后的半长轴初值, 30min短弧定轨和10min预报的卫星位置分量精度均优于4km, 能够满足非合作GEO目标机动后快速轨道恢复的需求. 相似文献
20.
射电天线指向精度通常要求小于主波束宽度的1/10, 对于短厘米波段或毫米波段的大口径反射面天线, 指向精度要求高达几个角秒, 对于天线性能目标的实现是个巨大的挑战, 因此对于大口径高频段的反射面天线来说指向问题成为天线性能实现的重要关注焦点. 在众多影响天线指向精度的结构子系统因素中, 对主反射面变形因素的研究很少. 文章结合天线的结构特点建立了反射面空间坐标系统, 并基于变形后主面点的空间坐标值, 提出了3自由度下的非线性最小二乘吻合的方法去精准预测天线指向. 最后利用空间几何关系严格推导出了服务于天线指向误差修正的俯仰和方位的精确调整量, 从而构建了主面变形同指向误差之间的间接关系, 这对大型射电天线指向精度的提升具有一定的指导意义. 相似文献