共查询到20条相似文献，搜索用时 140 毫秒
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时间尺度是通过综合众多精密时钟得到的。时间尺度的计算目前主要采用类ALGOS算法 ,这类算法的缺点是权值没有准确反映精密时钟噪声参数以及不能使五种噪声分量同时达到优化综合和不能形成实时的时间尺度。从精密时钟综合的优化算法原理出发 ,探讨了精密时钟噪声参数的估计、精密时钟噪声中噪声分量的分解等问题的解决方法 ,并由此提出了较优化的时间尺度算法 (精密时钟综合算法 ) ,还提出了对现有算法的改进意见。 相似文献
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激光时间传递技术的进展 总被引：4，自引：0，他引：4
激光时间传递技术是通过激光脉冲在空间的传播来实现地面与卫星时钟或地球上远距离两地时钟的同步，它具有很高的准确度和稳定度。一些国家已经成功进行了激光时间传递的试验，结果证明利用激光进行时钟之间的同步是有效可行的。介绍国内外已有的激光时间传递试验的情况和结果，重点介绍美国地面与机载原子钟之间的激光时间比对，以及法国的LASSO(LAser Synchronization from Stationary Orbit)和T2L2(Time Transfer by Laser Link)计划。 相似文献
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为保证正在调试中的低试中的低纬子午环的定时需要,我们研制了一套具有较高性能的ＧＰＳ精密守时系统,由ＧＰＳ、１ＭＣ频率源和一台自己研制的时钟提供精确到１ｍｓ的信号,用ＧＰＳ的秒信号时钟进行同步,由计算机完成时钟信号的全自动采集。系统的完成克服了由于钟房撤消而带来的定时的困难。为低纬子午环的顺利运动提供了较好的保障,同时也可适用于其它需要此类定时功能的观测场合。 相似文献
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基于VLBI资料的ERP高频变化求解方法的研究 总被引：1，自引：0，他引：1
在天测与测地VLBI资料分析软件CALC／SOLVE中，对地球自转参数(ERP)高频变化的解算采用了附加约束的连续分段线性拟合方法，即要求在两个历元节点之间ERP变化率小于某事先约定值，并要求ERP在历元节点上连续．实测资料分析表明，当资料点密度较低时，引入约束条件和要求连续均有助于提高解的稳定性，但也人为降低了解的客观性，使各历元节点ERP解算结果之间相关．为此，基于CALC／SOLVE的用户偏导功能，实现了ERP高频变化的直接求解模块，不附加约束，也不要求连续．实测资料分析表明对ERP高频变化的直接求解模式更为可取．对于长时段VLBI资料的ERP高频变化求解，需要考虑岁差和章动模型偏差(天极偏移)的影响，编写相应的求解模块，并成功实现了1979至2003年长时段ERP高频变化求解．比较表明，在考虑了岁差章动模型偏差的影响时能够显著提高解的精度．为此，在基于VLBI资料解算ERP高频变化时，建议采用直接求解模式，并考虑岁差章动模型偏差的影响． 相似文献
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V.I. Karpman B.I. Meerson A.B. Mikhailovsky O.A. Pokhotelov 《Planetary and Space Science》1977,25(6):573-585
Expressions for the ULF wave growth rates are obtained by consistent study of the bounce and drift motions of geomagnetically trapped particles. Different cases depending on the relative values of bounce, drift and wave frequencies are examined. It is shown that the growth (damping) rate as a function of wave frequency has an oscillatory character with maxima associated with an averaged bounce frequency. The instability conditions are investigated. For wave frequencies exceeding the Larmor drift frequency, the instability appears if the derivative function with respect to the energy is positive over a sufficient period. If, however, the wave frequency is less than an effective Larmor drift frequency, the instability is possible even if this derivative is negative everywhere. 相似文献
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V. N. Melnik A. A. Konovalenko V. V. Dorovskyy H. O. Rucker E. P. Abranin V. N. Lisachenko A. Lecacheux 《Solar physics》2005,231(1-2):143-155
The results of observations of solar decametric drift pair bursts are presented. These observations were carried out during
a Type III burst storm on July 11–21, 2002, with the decameter radio telescope UTR-2, equipped with new back-end facilities.
High time and frequency resolution of the back-end allowed us to obtain new information about the structure and properties
of these bursts. The statistical analysis of more than 700 bursts observed on 13–15 July was performed separately for “forward”
and “reverse” drift pair bursts. Such an extensive amount of these kind of bursts has never been processed before. It should
be pointed out that “forward” and “reverse” drift pair bursts have a set of similar parameters, such as time delay between
the burst elements, duration of an element, and instant bandwidth of an element. Nevertheless some of their parameters are
different. So, the absolute average value of frequency drift rate for “forward” bursts is 0.8 MHz s−1, while for “reverse” ones it is 2 MHz s−1. The obtained functional dependencies “drift rate vs. frequency” and “flux density vs. frequency” were found to be different
from the current knowledge. We also report about the observation of unusual variants of drift pairs, in particular, of “hook”
bursts and bursts with fine time and frequency structure. A possible mechanism of drift pairs generation is proposed, according
to which this emission may originate from the interaction of Langmuir waves with the magnetosonic waves having equal phase
and group velocities. 相似文献
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附有周期项的预报模型及其在GPS卫星钟差预报中的应用研究 总被引：5，自引：0，他引：5
为了有效进行GPS卫星钟差预报和更好地反映卫星钟差特性,除了考虑卫星原子钟频移、频漂和频漂率等物理性质外,还应考虑到卫星钟差的周期性变化特点.在二次多项式模型基础上,增加了周期项因素,构造了新的预报模型.选取部分GPS卫星铯钟(Cs.clock)和铷钟(Rb.clock)钟差资料,根据钟差变化趋势分3种情况,按不同时间长度进行钟差预报分析,并与二次多项式模型的预报结果比较分析,大量数据分析表明:附有周期项的二次多项式模型预报精度优于二次多项式模型,铷钟预报精度略优于铯钟. 相似文献
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A unified theory of low frequency instabilities in a two component (cold and hot) finite-β magnetospheric plasma is suggested. It is shown that the low frequency oscillations comprise two wave modes : compressional Alfvén and drift mirror mode. No significant coupling between them is found in the long-wave approximation. Instabilities due to spontaneous excitation of these oscillations are considered. It is found that the temperature anisotropy significantly influences the instability growth rate at low frequency. A new instability due to the temperature anisotropy and density gradient appears when the frequency of compressional Alfvén waves is close to the drift mirror mode frequency. The theoretical predictions are compared in detail with the Pc5 event of 27 October 1978 observed simultaneously by the GEOS 2 satellite and the STARE radar facility. It is shown that the experimental results can be interpreted in terms of a compressional Alfvén wave driven by the drift anisotropy instability. 相似文献
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The 13 pairs of type III bursts with the bidirectional drift structures recorded with the spectrograph in the frequency ranges of 230–300 MHz and 625–1500 MHz at the Yunnan Observatory and 2600–3800 MHz at the Beijing National Astronomical Observatories are analyzed in this present article and the outstanding characteristics of these events are obtained. These bursts respectively reveal that the separatrix frequency between the bursts with positive and negative drifts comes between 250 MHz and 3420 MHz, with a gap being between 0.6 MHz and 110 MHz; the duration is 53 ms–1880 ms and the frequency drift rate is between 45 MHz/s and 56000 MHz/s. The drift rate at metric wavelengths is relatively low, only a few decades of MHz while it is comparatively high at microwave wavelengths, reaching 56000 MHz/s. The qualitative explanation of these events is given in this paper. 相似文献
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An empirical model has been developed to reproduce the drift of the spectrum recorded by the EIS on Hinode using instrumental temperatures and relative motion of the spacecraft. The EIS spectrum shows an artificial drift in wavelength
dimension in sync with the revolution of the spacecraft, which is caused by temperature variations inside the spectrometer.
The drift amounts to 70 km s−1 in Doppler velocity and introduces difficulties in velocity measurements. An artificial neural network is incorporated to
establish a relationship between the instrumental temperatures and the spectral drift. This empirical model reproduces observed
spectrum shift with an rms error of 4.4 km s−1. This procedure is robust and applicable to any spectrum obtained with EIS, regardless of the observing field. In addition,
spectral curvatures and spatial offset in the north – south direction are determined to compensate for instrumental effects. 相似文献
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W. K. Yip 《Solar physics》1973,30(2):513-526
The radio emissions caused by electron streams in a non-isothermal plasma are studied quantitatively. It is proposed that conversion of the stream-excited plasma waves into electromagnetic waves by scattering on the thermal fluctuations at nonisothermal sonic oscillation frequency is the origin of the emission of the split-pair burst near the plasma frequency. The occurrence of the split-pair bursts near the second harmonic of the plasma frequency can be due to combination scattering of the stream-excited plasma waves by electron density fluctuations which are produced by the scattered plasma waves. With a streamer model in which the electron densities are two times those in Newkirk's model, both the observed frequency splitting and the rate of drift of the split pair can be explained as the result of plasma radiation caused by a stream of 10 keV electrons. A tentative model for the split-pair emission is suggested. 相似文献
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本文研究了寻常波和非常波在线性传播条件下，对快速毫秒级spike的时延、频漂和偏振逆转的影响．计算表明，在（20－40）×Baumbach－Alien的电子密度分布下，由于传播产生的时延，偏振逆转等约为30－300ms，这与观测结果在量级上是一致的．这说明在快速活动中传播效应是一个重要的因素． 相似文献
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On April 21, 2002, a broadband solar radio burst was observed at about 01:00 – 03:00 UT with the digital spectrometers of
National Astronomical Observatories of China (NAOC). Also many fiber bursts superposed on the continuum bursts were detected
in the frequency range of 2.6 – 3.8 GHz during the time interval. After data processing, some parameters of the fibers such
as frequency drift rate, duration, bandwidth, and relative bandwidth were determined. The mean value of the frequency drift
was in the range of 42.3 – 87.4 MHz s−1 (negative). A theoretical interpretation for the fibers was presented based upon a model of the velocity of Alfvén solitons.
In this model, the source of the fiber emission was considered as the ducting of the solitons within the magnetic-mirror loop.
Then the magnetic field strength of the fiber source was estimated to be about 130 ≤ B0 ≤ 270 G. Also a comparison of the magnetic field estimation was made with another model of whistler group velocity. 相似文献