全球定位系统的新进展(讲座四)——信号内部时延及其对钟差的影响     

李征航  龚晓颖 《测绘信息与工程》2012,37(4):51-54

介绍了卫星信号内部时延的定义以及在GPS导航电文NAV和CNAV中所给出的各种时延差参数,推导了采用不同的卫星信号测距时应采用的各种卫星钟差模型。  相似文献   

E-601B型蒸发量常见误差分析     

钟启琴  李尚锦  陈红梅  崔宗鸿 《四川气象》2010,(1):69-71

根据E-601B型蒸发器人工测定蒸发量近10年的工作经验,分析了在实际工作巾引起蒸发量常见误差的原因、观测中的注意事项,对获取真实、准确、连续的蒸发量数据具有一定参考作用。  相似文献   

Theoretical Basis and Application of an Analogue- Dynamical Model in the Lorenz System   总被引：2，自引：0，他引：2  

REN Hongli  CHOU Jifan  HUANG Jianping  ZHANG Peiqun 《大气科学进展》2009,26(1):67-77

The theoretical basis and application of an analogue-dynamical model (ADM) in the Lorenz system is studied. The ADM can effectively combine statistical and dynamical methods in which the small disturbance of the current initial value superimposed on the historical analogue reference state can be regarded as a prediction objective. Primary analyses show that under the condition of appending disturbances in model parameters, the model errors of ADM are much smaller than those of the pure dynamical model (PDM). The characteristics of predictability on the ADM in the Lorenz system are analyzed in phase space by conducting case studies and global experiments. The results show that the ADM can quite effectively reduce prediction errors and prolong the valid time of the prediction in most situations in contrast to the PDM, but when model errors are considerably small, the latter will be superior to the former. To overcome such a problem, the multi-reference-state updating can be applied to introduce the information of multi-analogue and update analogue and can exhibit exciting performance in the ADM.  相似文献   

Characteristics of tropical Pacific SST predictability in coupled GCM forecasts using the NCEP CFS     

Emilia K. Jin  James L. Kinter III 《Climate Dynamics》2009,32(5):675-691

The limits of predictability of El Niño and the Southern Oscillation (ENSO) in coupled models are investigated based on retrospective forecasts of sea surface temperature (SST) made with the National Centers for Environmental Prediction (NCEP) coupled forecast system (CFS). The influence of initial uncertainties and model errors associated with coupled ENSO dynamics on forecast error growth are discussed. The total forecast error has maximum values in the equatorial Pacific and its growth is a strong function of season irrespective of lead time. The largest growth of systematic error of SST occurs mainly over the equatorial central and eastern Pacific and near the southeastern coast of the Americas associated with ENSO events. After subtracting the systematic error, the root-mean-square error of the retrospective forecast SST anomaly also shows a clear seasonal dependency associated with what is called spring barrier. The predictability with respect to ENSO phase shows that the phase locking of ENSO to the mean annual cycle has an influence on the seasonal dependence of skill, since the growth phase of ENSO events is more predictable than the decay phase. The overall characteristics of predictability in the coupled system are assessed by comparing the forecast error growth and the error growth between two model forecasts whose initial conditions are 1 month apart. For the ensemble mean, there is fast growth of error associated with initial uncertainties, becoming saturated within 2 months. The subsequent error growth follows the slow coupled mode related the model’s incorrect ENSO dynamics. As a result, the Lorenz curve of the ensemble mean NINO3 index does not grow, because the systematic error is identical to the same target month. In contrast, the errors of individual members grow as fast as forecast error due to the large instability of the coupled system. Because the model errors are so systematic, their influence on the forecast skill is investigated by analyzing the erroneous features in a long simulation. For the ENSO forecasts in CFS, a constant phase shift with respect to lead month is clear, using monthly forecast composite data. This feature is related to the typical ENSO behavior produced by the model that, unlike the observations, has a long life cycle with a JJA peak. Therefore, the systematic errors in the long run are reflected in the forecast skill as a major factor limiting predictability after the impact of initial uncertainties fades out.  相似文献   

一种发射车快速精确定位定向技术的研究     

白云超  张晓明  吕妍红  李魁  赵荣 《测绘科学》2009,34(2)

目前发射车的定位定向普遍采用GPS、惯导及寻北仪等测量方法或后方交汇解算方法。测量法易受干扰、精度低而且寻北时间长;而解算法没有研究经纬仪存在姿态倾角时测量点三维坐标及载体姿态角的求解问题。本文提出了一种新的导弹发射车快速精确定位定向的方法:首先利用捷联安装在车体上的光电探测器,分别探测地面上三个坐标位置已知的靶标,得到三组方位角和俯仰角,并结合车载导航设备给出的发射车概略坐标、姿态角信息解算出发射车更精确的坐标、姿态角。通过实验研究论证,表明此方法具有速度快、精度高、自动化及智能化程度高的特点,能够有效缩短发射车准备时间、提高导弹发射的反应速度。  相似文献   

我国深度基准面不统一所带来的问题与对策     

吴俊彦  韩范畴  成俊  孙国勇 《海洋测绘》2008,28(4):54-56

简述了深度基准面的概念，分析了海图深度基准面不统一造成的误差及其形成原因。针对海图深度基准面的使用现状，探讨了深度基准面不统一对海洋测绘成果应用的影响，提出了统一海图深度基准面的方案和建议。  相似文献   

On comparison of the Earth orientation parameters obtained from different VLBI networks and observing programs   总被引：1，自引：1，他引：0  

Z. Malkin 《Journal of Geodesy》2009,83(6):547-556

In this paper, a new geometry index of very long baseline interferometry (VLBI) observing networks, the volume of network V, is examined as an indicator of the errors in the Earth orientation parameters (EOP) obtained from VLBI observations. It has been shown that both EOP precision and accuracy can be well described by the power law σ = aV ^c in a wide range of the network size from domestic to global VLBI networks. In other words, as the network volume grows, the EOP errors become smaller following a power law. This should be taken into account for a proper comparison of EOP estimates obtained from different VLBI networks. Thus, performing correct EOP comparison allows us to investigate accurately finer factors affecting the EOP errors. In particular, it was found that the dependence of the EOP precision and accuracy on the recording data rate can also be described by a power law. One important conclusion is that the EOP accuracy depends primarily on the network geometry and to lesser extent on other factors, such as recording mode and data rate and scheduling parameters, whereas these factors have a stronger impact on the EOP precision.  相似文献   

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陈轲  归庆明  杨娜 《大地测量与地球动力学》2009,29(3):114-118

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一种Kalman滤波系统误差及其协方差矩阵的半参数估计方法   总被引：1，自引：0，他引：1  

曹轶之  隋立芬  范澎湃 《测绘科学》2009,34(2)

提出用半参数估计理论来解决系统误差对Kalman滤波解的影响问题。即用半参数模型中的非参数分量表达观测模型和动力学模型中未知的系统误差,在移动的窗口内,基于观测残差和状态向量预测残差拟合模型系统误差,进而修正相应的观测向量和状态预测向量的协方差矩阵,以消除系统误差对滤波的影响。同时这种方法还有明显的优点,就是在滤波过程中不需要对系统误差做任何假设。文中推导了基于正则核估计来解算导航系统半参数模型的相应公式,并根据一个模拟的算例,证明了算法的有效性。  相似文献   

Systematic errors in the medium range prediction of the Asian summer monsoon circulation     

U. C. Mohanty  K. J. Ramesh 《Journal of Earth System Science》1995,104(1):49-77

The present study describes an analysis of Asian summer monsoon forecasts with an operational general circulation model (GCM) of the European Centre for Medium Range Weather Forecasts (ECMWF), U.K. An attempt is made to examine the influence of improved treatment of physical processes on the reduction of systematic errors. As some of the major changes in the parameterization of physical processes, such as modification to the infrared radiation scheme, deep cumulus convection scheme, introduction of the shallow convection scheme etc., were introduced during 1985–88, a thorough systematic error analysis of the ECMWF monsoon forecasts is carried out for a period prior to the incorporation of such changes i.e. summer monsoon season (June–August) of 1984, and for the corresponding period after relevant changes were implemented (summer monsoon season of 1988). Monsoon forecasts of the ECMWF demonstrate an increasing trend of forecast skill after the implementation of the major changes in parameterizations of radiation, convection and land-surface processes. Further, the upper level flow is found to be more predictable than that of the lower level and wind forecasts display a better skill than temperature. Apart from this, a notable increase in the magnitudes of persistence error statistics indicates that the monsoon circulation in the analysed fields became more intense with the introduction of changes in the operational forecasting system. Although, considerable reduction in systematic errors of the Asian summer monsoon forecasts is observed (up to day-5) with the introduction of major changes in the treatment of physical processes, the nature of errors remain unchanged (by day-10). The forecast errors of temperature and moisture in the middle troposphere are also reduced due to the changes in treatment of longwave radiation. Moreover, the introduction of shallow convection helped it further by enhancing the vertical transports of heat and moisture from the lower troposphere. Though, the hydrological cycle in the operational forecasts appears to have enhanced with the major modifications and improvements to the physical parameterization schemes, certain regional peculiarities have developed in the simulated rainfall distribution over the monsoon region. Hence, this study suggests further attempts to improve the formulations of physical processes for further reduction of systematic forecast errors.  相似文献