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1.
The campaigns of the programme of international cooperation, called MERIT, for the determination of the earth rotation parameters are reviewed, especially about the difficulties to infer results about polar motion from such short intervals of observations. It is pointed out the need to employ the same models and standards in order to facilitate the comparison of data obtained by classical and modern techniques.  相似文献   

2.
由于空间大地观测数据传输耗时及处理过程复杂, 导致极移测量值的获取存在时延, 无法满足对高精度的极移预报值有重大需求的应用领域. 针对极移复杂的时变特性, 提出一种基于奇异谱分析(singular spectrum analysis, SSA)的预报方法. 首先用SSA分离提取极移时序中的高频组分与低频组分; 其次建立最小二乘(least square, LS)外推与自回归(AutoreGressive, AR)模型对极移高频和低频组分进行组合预报. 结果表明, SSA方法能够准确地分离和提取极移低频和高频组分, 对低频和高频组分组合预报可以显著改善极移的中长期(30--365d)预报精度, 与国际地球自转和参考系服务局(International Earth Rotation and Reference Systems Service, IERS)提供的A公报中的极移预报值相比, SSA方法对极移PMX分量(本初子午线方向)和PMY分量(西90$^\circ$子午线方向)的中长期预报精度改进最高分别可达45.97%和62.44%. 研究结果验证了SSA方法对极移中长期预报改进的有效性.  相似文献   

3.
极移的变化与多种激发息息相关,这些激发包括大气表面压力和大气风、海底压力和洋流、陆地水分布以及气候变暖导致的海平面变化,并且可以通过有效角动量函数来估计.在极移预报中,通过刘维尔方程融合有效角动量函数,并利用最小二乘与自回归组合的方法进行拟合及外推,同时,对自回归模型的可调节参数设置更多的选择,在不同的极移预报阶段,对于不同分量的预报匹配更优的参数,有效地提高了极移的预报精度.在441次1–90 d的极移预报实验中,短中期的预报改善更为明显,在1–6 d和7–30 d的极移X预报结果中,分别有56.9%和53.5%优于国际地球自转服务(International Earth Rotation Service, IERS)的预报;在1–6 d和7–30 d的极移Y预报结果中,分别有66.5%和59.7%优于IERS的预报.整体上,极移Y的预报精度比极移X的预报精度有更多的提升,以IERS的地球定向参数(Earth Orientation Parameters, EOP)产品EOP 14C04 (IAU2000A)为参考,极移X预报在第1 d、第5 d的MAE (Mean Absolute...  相似文献   

4.
大气对地球自转参数（ERP）的高频激发   总被引：4，自引：0，他引：4  
谢伯全  郑大伟 《天文学报》1996,37(2):113-123
本文采用１９８３—１９９２年期间由空间大地测量技术观测和归算的地球自转参数（ＥＲＰ）序列，以及由全球气象资料归算的大气角动量（ＡＡＭ）序列，分析和研究了大气对地球自转参数的日长变化（ＬＯＤ）和极移（ｘ和ｙ）在一个月时间尺度以内的高频激发作用，得到的主要结果如下：１大气对ＬＯＤ分量高频潮汐的估计值存在着影响，但是，潮汐形变参数ｋ／ｃ随时间和频率的变化却是受非大气因素的扰动引起的．２．大气可以解释３０天以下ＬＯＤ非潮汐的大部分变化．３．极移分量３０天以内的高频变化也主要由大气激发．ｘ分量与大气的相关性要强于ｙ分量，而且更为稳定，主要表现为平均时间尺度约为２７天的波动，大气对这个波动的贡献可达７０％．  相似文献   

5.
针对目前极移最小二乘(Least Square, LS)+自回归(AutoRegressive, AR)预报模型的单一数据选取方案, 提出分别考虑LS模型数据量和AR残差数据量的组合数据模式, 并对极移预报时单一数据和组合数据预报结果精度进行分析, 探讨模型输入数据量对极移预报精度的影响. 结果表明, 模型输入数据量的变化对极移预报结果影响较大. 采用组合数据预报的方式相比较于单一数据量预报方式精度更高, 特别是针对30--360 d跨度内的中长期预报, 组合数据量的极移预报精度可比单一数据量预报精度有较大改善. 结论证明组合数据在极移预报时具有一定的优势, 可为以后极移预报数据量选取提供一定的借鉴参考意义.  相似文献   

6.
孙付平  赵铭 《天文学进展》1995,13(2):132-142
简要阐述了用空间大地测量方法测量和研究现代板块运动的理论、方法和进展。简单介绍了测定原理和实测现状，以及用实测资料建立板块运动模型的理论和方法；重点讨论了板块运动在最近十几年的研究进展；对目前存在的问题及未来的发展作了简要评述。  相似文献   

7.
The work studies the Chandler component of polar motion, obtained from variations in the Pulkovo latitude over 170 years (1840–2009). To extend the time series of variations in the Pulkovo latitude back into the past until 1840, we used the first Pulkov observations on the basis of the Reynolds transit instrument in the prime vertical and on the basis of large vertical Ertel circle. We employed different methods of analysis of nonstationary time series, such as wavelet analysis, methods of bandpass filtering, singular spectral analysis, and Fourier and Hilbert transforms. Changes in the Pulkovo latitude from 1904–2006, as inferred from ZTF-135 observations and as calculated from international data, were compared. It was shown that time changes in the amplitude and phase of Chandler polar motion can be studied based on long-term observation time series of latitude at a single observatory, even if these observation records have gaps. We were the first to study the changes in the Chandler wobble for that long time series of variations in the Pulkovo latitude with the help of different methods. The long observation record and the methods of analysis of nonstationary time series had allowed us to identify two similar structures, both well apparent during the periods of 1845–1925 and 1925–2005 in the time variations of phase and amplitude. The presence of this structure indicates that low-frequency regularities may be present in the Chandler polar motion, and one of the manifestations of this may be the well known feature in the region of 1925. The superimposed epoch method was used to estimate the period of variations in the amplitude with a simultaneous change of phase of this oscillation, which was found to be 80 years. In addition, advantages of singular spectral analysis for studying the long-period time series with involved structure are demonstrated.  相似文献   

8.
D. Boutin  J. Arkani-Hamed 《Icarus》2006,181(1):13-25
We use the mapping-phase high-altitude magnetic measurements provided by Mars Global Surveyor (MGS) between March 1999 and April 2003 to model nine relatively isolated magnetic anomalies of Mars. Each anomaly is modeled with an elliptical prism. Each component of the observed magnetic field is modeled independently using an elliptical prism in order to assess the reliability of the results and suppress non-crustal and nearby crustal source contaminations. The paleomagnetic pole positions are obtained from the magnetization vectors of the model source bodies. We clean the data by removing the bad tracks and then divide the entire data into two sets that are measured at different times. Applying covariance analysis in the Fourier domain to two maps of the same magnetic component that are derived from the two sets provides a means to extract the most common features of the maps. The quality of a model is evaluated and only good models are used in the final geophysical interpretation. Most poles that come from good models cluster in the Tharsis region, suggesting that Mars experienced polar motion since the magnetic source bodies were magnetized.  相似文献   

9.
The aim of this article is to draw attention to the priority of the well-known astronomer and geophysicist, member of the Academy of Sciences of Ukraine A.Ya. Orlov (1880–1954) in the determination of the following parameters describing the secular motion of the earth’s poles: speed (4 mas/year) and direction (69° west). These results (1954) are based on the astronomical observations from 1900 to 1950 with zenith telescopes at international latitude stations. Orlov is well known in the world astronomical community as the founder of the Poltava Gravimetric Observatory, the Main Astronomical Observatory, and the national research school of global geodynamics. However, his pioneering work on secular polar motion is little known worldwide. At present, Orlov’s estimates for secular polar motion have been verified by century-long observations (1900–2012) obtained with different telescopes at many observatories worldwide and by different, both astronomical and space-based, methods (LLS, VLBI, GNSS, etc.).  相似文献   

10.
We compute the weak stability boundary in the planar circular restricted three-body problem starting from the algorithmic definition, and its generalization by García and Gómez. In addition, we consider a new set of primaries, Sun–Jupiter, to replace the case of Earth–Moon considered in previous studies. Numerical enhancements are described and compared to previous methods. This includes defining the equations of motion in polar coordinates and a modified numerical scheme for the derivation of both stable sets and their boundaries. These enhancements decrease the computational time. New results are obtained by considering the Sun–Jupiter case which we compare to the Earth–Moon case.  相似文献   

11.
This paper describes methods for combining independent observations of polar motion into a single time series, and applies these methods to satellite laser ranging, Doppler, and astrometric polar motion data taken over the period 1981--1983. The polar motion data are treated as complex valued time series, yielding one estimate of the noise level for each series, rather than a separate estimate for X and Y components. Estimates of the noise level which take advantage of the existence of simultaneous observations are preferred. Linear combination of the data may be performed in both the time and the frequency domain, and examples of each are present. The results of analyzing three years of observations show little difference between the Allan and conventional variance. Present day Doppler determinations do not show marked improvement compared to classical astrometric results. Thus, the astrometric observations are still useful.  相似文献   

12.
Satellite orbital perturbations due to many rotations of the planet-fixed reference frame are calculated by a general analytical method. For the International Terrestrial Reference Frame (ITRF) the effects of the Earth irregular rotation, precession, nutation, and polar motion are considered. Gravity coefficients of the Earth potential expansion are expressed in an inertial Celestial Reference Frame (CRF) as functions of the set of standard constant coefficients derived in the ITRF and of the rotation angles between the CRF and ITRF. The analytical motion theory uses time dependent gravity coefficients, and the Lagrange motion equations are integrated in the CRF, as it is done by numerical methods. Comparison of the proposed analytical method with a numerical one is presented. Motion of the ETALON-1 geodetic satellite perturbed by the geopotential (36*36) and by the full effects of the Earth irregular rotation, precession, nutation and polar motion is predicted. The r.m.s. difference between the satellite's coordinates calculated by both methods over a year interval is 2 cm. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

13.
A new analytical method for calculating satellite orbital perturbations due to different disturbing forces is developed. It is based on the Poincaré method of small parameter but takes advantages of modern high-performance computers and of the tools of computer algebra. All perturbations proportional up to and including the 5th-order of small parameters are obtained. The method can precisely calculate the effects of all geodynamical forces on satellite motion given by the most up-to-date IAU and IERS models, such as non-central Earth gravity potential, precession and nutation of the geoequator, polar motion and irregularities in the Earth's rotation, effect of ocean and solid Earth tides, pole tide, and secular variations of gravity coefficients.Numerical tests prove the method's accuracy to be equivalent to 1–2 cm when calculating positions of high altitude geodetic satellites (like ETALON), and/or of GLONASS navigational spacecraft. The accuracy is stable over 1 year at least and comparable to that of the best tracking measurements of satellites.Positions of low altitude geodynamical satellites (like STARLETTE) by the analytical method are calculated to an accuracy of about 70cm over a month's interval. The method is developed for future use in GLONASS/GPS on-board ephemeris computation where it can improve the current scheme of their flight control.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

14.
The light variability is one of the main characteristics of blazar objects. Because of the complexity of their light curves, the present periodicity analysis methods are not yet perfect. Based on the modern spectral estimate theory, this paper has described in details the principles of the maximum entropy spectral estimate and autoregressive (AR) spectral estimate, analyzed the effect of the order number selection on the resultant model. Applying these methods to the periodicity analysis of the quasar 3C 279 and BL Lac object OJ 287, their light periods are obtained to be 7.14 and 11.76 yr, respectively. As is verified by experiments, the AR spectral estimate has a high resolution and is a rather good periodicity analysis method. Finally, the items noteworthy for the application of these spectrum estimation methods to the periodicity analysis of the light variations of blazars are mentioned.  相似文献   

15.
Jafar Arkani-Hamed 《Icarus》2009,204(2):489-498
We investigate the polar wander of Mars in the last ∼4.2 Ga. We identify two sets of basins from the 20 giant impact basins reported by Frey [Frey, H., 2008. Geophys. Res. Lett. 35, L13203] which trace great circles on Mars, and propose that the great circles were the prevailing equators of Mars at the impact times. Monte Carlo tests are conducted to demonstrate that the two sets of basins are most likely not created by random impacts. Also, fitting 63,771 planes to randomly selected sets of 5, 6, or 7 basins indicated that the identified two sets are unique. We propose three different positions for the rotation pole of Mars, besides the present one. Accordingly, Tharsis bulge was initially formed at ∼50 N and moved toward the equator while rotating counterclockwise due to the influence of the two newly forming volcanic constructs, Alba Patera and Elysium Rise. The formation of the giant impact basins, subsequent mass concentrations (mascons) in Argyre, Isidis, and Utopia basins, and surface masses of volcanic mountains such as Ascraeus, Pavonis, Arsia and Olympus, caused further polar wander which rotated Tharsis bulge clockwise to arrive at its present location. The extensive polar motion of Mars during 4.2-3.9 Ga implies a weak lithosphere on a global scale, deduced from a total of 72,000 polar wander models driven by Tharsis bulge, Alba Patera and Elysium Rise as the major mass perturbations. Different compensation states, 0-100%, are examined for each of the surface loads, and nine different thicknesses are considered for an elastic lithosphere. The lithosphere must have been very weak, with an elastic thickness of less than 5 km, if the polar wander was driven by these mass perturbations.  相似文献   

16.
针对大口径、高性能射电望远镜天线受到的随机及时变风扰的问题, 利用自回归滑动平均模型预测望远镜周围风速, 提前计算风致结构变形量, 同时为望远镜伺服控制系统提供足够执行时间来降低风扰影响. 基于新疆奇台110m口径全向可动射电望远镜(QiTai Telescope, QTT)台址风场数据特征, 通过赤池信息准则和贝叶斯信息准则辨识模型阶次, 利用最大似然法估计模型参数, 分析模型残差特性以检验自回归滑动平均模型的有效性. 通过计算不同季度预测数据与测试数据偏差得到预测模型的精度, 夏季平均绝对误差为0.133mcdots-1, 秋季平均绝对误差为0.162mcdots-1, 冬季平均绝对误差为0.287mcdots-1. 整体来看, 基于QTT台址不同季度风速数据建立的自回归滑动平均模型预测误差较小, 满足射电望远镜风扰控制系统的需求, 能为大口径射电望远镜风扰控制提供必要数据支撑.  相似文献   

17.
In this paper we discuss the influence of the triaxiality of a celestialbody on its free rotation, i.e. in absence of any external gravitationalperturbation. We compare the results obtained through two different analytical formalisms, one established from Andoyer variables by usingHamiltonian theory, the other one from Euler's variables by usingLagrangian equations. We also give a very accurate formulation of thepolar motion (polhody) in the case of a small amplitude of this motion.Then, we carry out a numerical integration of the problem, with aRunge–Kutta–Felberg algorithm, and for the two kinds of methods above, that we apply to three different celestial bodies considered as rigid : the Earth, Mars, and Eros. The reason of this choice is that each of this body corresponds to a more or less triaxial shape.In the case of the Earth and Mars we show the good agreement betweenanalytical and numerical determinations of the polar motion, and theamplitude of the effect related to the triaxial shape of the body, whichis far from being negligible, with some influence on the polhody of theorder of 10 cm for the Earth, and 1 m for Mars. In the case of Eros, weuse recent output data given by the NEAR probe, to determine in detailthe nature of its free rotational motion, characterized by the presence ofimportant oscillations for the Euler angles due to the particularly largetriaxial shape of the asteroid.  相似文献   

18.
A reasonable and quantitative result on the variation of polar wobble excited by the oceans is not available at present. Numerous researches have shown that atmospheric motion is the greatest excitation source for the seasonal variations in the polar wobble and that oceanic motion is one of the main remaining excitation sources. The excitation of variation in the annual polar wobble caused by oceans from 1992 to 2004 both globally and in latitude dependence, have been studied in depth by means of the new generation of SODA oceanic data assimilation (SODA-1.4.2 and SODA-1.4.3) and the ECCO oceanic data assimilation. The result shows that the variation in the seasonal polar wobble excited by the SODA oceans is very close to that of the residual after the action of the atmosphere and land water is deducted from the geodesic excitation function for a large part of the investigated time interval, and that there is overall agreement between the two as regards the annual amplitude and phase. In addition, in comparison with the result of early SODA-Bata 7, the new generation of SODA oceanic excitation has achieved obvious improvements. The latitude distributions of the excitations of the annual polar wobble by the SODA and ECCO oceans are consistent in the Greenwich direction, while having obvious differences in the direction of 90° E.  相似文献   

19.
This review is essentially a bibliography. In the first part, work done locally on period-finding methods is discussed. Some of the topics referred to are: periodogram significance testing, identification of non-sinusoidal periodicities, and computational shortcuts useful for calculating periodograms of large data sets. A number of aspects of period-finding in ray astronomy are briefly mentioned: these include various test statistics for the presence of a periodicity, the influence of oversampling on significance levels, estimation of the pulse shape, and the specification of a flux limit in the case of a non-detection. The second part of the review deals with the analysis of stochastic astronomical time series. Topics dealt with are ARMA modelling, Kalman filtering, problems associated with O-C analyses, and continuous time ARMA modelling. Two aspects of bivariate astronomical time series are touched on, namely time domain transfer function modelling and the estimation of the lag between two irregularly observed series.  相似文献   

20.
The global oceans play important roles in exciting the annual polar motion besides the atmosphere. However,it is still unclear about how large the regional oceans contribute to the annual polar motion. We investigate systemically the contributions of the Pacific,Atlantic and Indian Oceans to the excitation of the annual polar motion,based on the output data of ocean current velocity field and ocean bottom pressure field from "Estimating the Circulation and Climate of the Ocean (ECCO)" ocean circulation model over the period 1993-2005. The result shows that due to its particular location and shape,the Atlantic Ocean makes a less significant contribution to the x-component of the annual polar motion excitation than the Pacific and Indian Oceans,while all these three oceans contribute to the y-component of the annual polar motion excitation to some extent.  相似文献   

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