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1.
精密时钟单钟幂律谱系数的取值分析 总被引:3,自引:1,他引:2
精密时钟噪声可用五个幂律谱系数来表征其强弱。由于不存在实际可用的理想时钟作为参考,用以估计幂律谱系数的单钟噪声无法直接测出,而只能利用钟组内各钟之间的钟差。然而这是一个不适定问题.本文探讨了单钟幂律谱系数的取值范围与优化估计方法。 相似文献
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该文介绍了目前上海天文台正在研制的小型氢原子钟的监控系统。它可监控氢钟的工作情况,实现氢钟的自动启闭、参数自动检测、自动报警,可控制综合器的频率变化、微波腔温度、氢离子流的大小。 相似文献
4.
Failure time variation derived from R–S relation: the role of the static stress perturbation 下载免费PDF全文
In general, earthquake cycle related to earthquake faulting could include four major processes which could be described by (1) fault locking, (2) self-acceleration or nucleation (possible foreshocks), (3) coseismic slip, and (4) post-stress relaxation and afterslip. A sudden static stress change/perturbation in the surrounding crust can advance/delay the fault instability or failure time and modify earthquake rates. Based on a simple one-dimensional spring-slider block model with the combination of rate-and-state-dependent friction relation, in this study, we have approximately derived the simple analytical solutions of clock advance/delay of fault failures caused by a sudden static Coulomb stress change applied in the different temporal evolution periods during an earthquake faulting. The results have been used in the physics-based explanation of delayed characteristic earthquake in Parkfield region, California, in which the next characteristic earthquake of M 6.0 after 1966 occurred in 2004 instead of around 1988 according to its characteristic return period of 22 years. At the same time, the analytical solutions also indicate that the time advance/delay in Coulomb stress change derived by the dislocation model has a certain limitation and fundamental flaw. Furthermore, we discussed the essential difference between rate- and state-variable constitutive (R–S) model and Coulomb stress model used commonly in current earthquake triggering study, and demonstrated that, in fact, the Coulomb stress model could be involved in the R–S model. The results, we have obtained in this study, could be used in the development of time-dependent fault interaction model and the probability calculation related to the time-dependent and renewal earthquake prediction model. 相似文献
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Marek Ziebart Paul Cross Antony Sibthorpe Peter Arrowsmith Washington Ochieng Shaojun Feng Umar Bhatti Peter Niemann 《GPS Solutions》2007,11(4):227-237
The Galileo integrity chain depends on a number of key factors, one of which is contamination of the signal-in-space errors
with residual errors other than imperfect modelling of satellite orbits and clocks. A potential consequence of this is that
the user protection limit is driven not by the errors associated with the imperfect orbit and clock modelling, but by the
distortions induced by noise and bias in the integrity chain. These distortions increase the minimum bias the integrity chain
can guarantee to detect, which is reflected in the user protection limit. A contributor to this distortion is the inaccuracy
associated with the estimation of the offset between the Galileo sensor station (GSS) receiver clocks and the Galileo system
time (GST). This offset is termed the receiver clock synchronization error (CSE). This paper describes the research carried
out to determine both the CSE and its associated error using GPS data as captured with the Galileo System Test Bed Version
1 (GSTB-V1). In the study we simulate open access to a time datum using IGS data. Two methods are compared for determining
CSE and the corresponding uncertainty (noise) across a global network of tracking stations. The single-epoch single-station
method is an ‘averaging’ technique that uses a single epoch of data, and is carried out at individual sensor stations, without
recourse to the data from other stations. The global network solution method is also single epoch based, but uses the inversion
of a linearised model of the global system to solve for the CSE simultaneously at all GSS along with a number of other parameters
that would otherwise be absorbed into the CSE estimate in the averaging technique. To test the effectiveness of various configurations
in the two methods the estimated synchronisation errors across the GSS network (comprising 25 stations) are compared to the
same values as estimated by the International GPS Service (IGS) using a global tracking network of around 150 stations, as
well as precise orbit and satellite clock models determined by a combination of global analysis centres. The results show
that the averaging technique is vulnerable to unmodelled errors in the satellite clock offsets from system time, leading to
receiver CSE errors in the region of 12 ns (3.7 m), this value being largely driven by the satellite CSE errors. The global
network approach is capable of delivering CSE errors at the level of 1.5 ns (46 cm) depending on the number of parameters
in the linearised model. The International GNSS Service (IGS) receiver clock estimates were used as a truth model for comparative
assessment. 相似文献
7.
GPS 导航电文中时间参数的变化特点 总被引:2,自引:0,他引:2
GPS导航电包含有GPS卫星的位置参数和时间参数,是定位,定时用户都必须使用的,随着GPS的改进,导航电民有所变,GPS导航电中时间参数的变化特点及SA对卫星钟的影响是这里着重讨论的内容。 相似文献
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对自1991年以来,在上海天文台氢原子钟上使用的热敏电阻控温系统的几个相关问题进行了讨论与分析。该系统的控温精度可达±5%,粗测温度复制性优于±3‰。 相似文献
10.
With the increasingly high requirement of clock source accuracy for seismic data servers and equipment, the development of a multipurpose timing system is urgently needed in the seismic industry. We have developed low-cost timing equipment according to the actual earthquake industry situation. This set of timing equipment can provide a unified solution to the different environment and different earthquake instruments with different timing precision demands. 相似文献