差分观测与伪距观测的定位精度

严格论证了在对空间或地面目标的定位中，利用伪距测量观测模型的几何因子大于用台站间一次差分观测模型的几何因子．此外，台站间完全差分测量观测的定位精度优于不完全测量情形的定位精度．这些结果给人们在实际工作中采取何种定位方式提供了可靠的理论依据．

一种基于位置信号线性拟合差分滤波器串联的二阶差分角加速度观测器

角加速度闭环能增加伺服控制系统的刚度,提高系统鲁棒性,但位置信号的二阶差分运算会放大高频噪声幅值,限制了加速度闭环在实际控制中的应用。首先,对三种基于多项式曲线拟合的角加速度观测器性能进行了分析,结果表明二次多项式角加速度观测器具有最优的综合性能;其次,为了抑制噪声,提出了一种基于位置信号线性拟合的串联二阶差分角加速度观测器,从截止频率、白噪声放大倍数和延时时间三个方面对其性能进行了分析,并与二次多项式角加速度观测器进行了对比,仿真和实验均验证了该方法具有更好的噪声抑制能力。

基于三差观测值的卡尔曼滤波算法研究与实现

作为一种全新的动态变形监测方法,GPS具有独特的优越性,它克服了传统的动态变形监测方法精度、实时、同步无法保证的缺陷,且提高了精度和实时性。本文基于载波相位三差观测值,采用卡尔曼滤波的数据处理方法,详细推导了利用GPS观测值实现动态变形监测的数学模型。

Research of the wave measurement using GPS absolute velocity estimation technology

This paper analyzed the existing methods of wave measurement, and described the advantages of GPS applied in measuring the wave. The equations of absolute velocity estimation were discussed, focusing on two methods with Doppler shill. The error sources and their effect on velocity estimation were analyzed. Then, some tests were carried on to simulate dynamic velocity determination using static data Based on the high-frequency carrier-phase derived Doppler observations, the velocity has been estimated to the precision of 1 cm/s or so, even to the mm/s level. And with the receiver generated Doppler measurements, the precision can reach 3 - 15 cm/s.

GPS二次差数据分析

根据在加拿大国家研究院(NRC),美国国家标准局(NBS)和美国海军天文台(USNO)之间通过不同GPS卫星和不同跟踪时间的共视测量数据,计算和分析了"一般二次差"和"时刻间二次差"观测量.借助于一些有意义的结果,人们可以加深对GPS各项误差源的认识.本文提出了利用单通道接收机得到"卫星间二次差"的"伪同步"方法,并建议了一种把两台站间所有时间比对共视测量数据结合在一起的无偏差权平均计算方法.

Feasibility of central loop TEM method for prospecting multilayer water-fi lled goaf

With deep mining of coal mines, prospecting multilayer water-filled goaf has become a new content that results from geophysical exploration in coalfields. The central loop transient electromagnetic （TEM） method is favorable for prospecting conductive layers because of the coupling relationship between its field structure and formation. However, the shielding effect of conductive overburden would not only require a longer observation time when prospecting the same depth but also weaken the anomalous response of underlying layers. Through direct time domain numerical simulation and horizontal layered earth forward modeling, this paper estimates the length of observation time required to prospect the target, and the distinguishable criterion of multilayer water-filled goal is presented with observation error according to the effect of noise on observation data. The observed emf curves from Dazigou Coal Mine, Shanxi Province can distinguish multilayer water-filled goaf. In quantitative inversion interpretation of observed curves, using electric logging data as initial parameters restrains the equivalence caused by coal formation thin layers. The deduced three-layer and two-layer water-filled goals are confirmed by the drilling hole. The result suggests that when observation time is long enough and with the anomalous situation of underlying layers being greater than the observation error, the use of the central loop TEM method to orosoect a multilaver water-filled goaf is feasible.

Generalized Square Conservative Multistep Finite Difference Scheme Incorporating Historical Observations

In this paper,a multistep finite difference scheme has been proposed,whose coefficients are determined taking into consideration compatibility and generalized quadratic conservation,as well as incorporating historical observation data.The schemes have three advantages:high-order accuracy in time,generalized square conservation,and smart use of historical observations.Numerical tests based on the one-dimensional linear advection equations suggest that reasonable consideration of accuracy,square conservation,and inclusion of historical observations is critical for good performance of a finite difference scheme.

Comprehensive Study on the Estimation of the Variance Components of Traverse Nets

This paper advances a new simplified formula for estimating variance components ,sums up the basic law to calculate the weights of observed values and a circulation method using the increaments of weights when estimating the variance components of traverse nets,advances the charicteristic roots method to estimate the variance components of traveres nets and presents a practical method to make two real and symmetric matrices two diagonal ones.

Algorithm for Harmonic Tidal Analysis along T/P Tracks： Taking Differences of Observed Sea Surface Heights at Adjacent Points as Observations

An algorithm （differential mode） is presented for the improvement of harmonic tidal analysis along T/P tracks, in which the differences between the observed sea surface heights at adjacent points are taken as observations. Also, the observation equations are constrained with the results of the crossover analysis; the parameter estimations are performed at 0.1° latitude intervals by the least squares. Cycle 10 to 330 T/P altimeter data covering the China Sea and the Northwest Pacific Ocean （2°-50° N,105°-150° E） are adopted for a refined along-track harmonic tidal analysis, and harmonic constants of 12 constituents in 8 474 points are obtained, which indicates that the algorithm can efficiently remove non-tidal effects in the altimeter observations, and improve the precision of tide parameters. Moreover, parameters along altimetry tracks represent a smoother distribution than those obtained by traditional algorithms. The root mean squares of the fitting errors between the tidal height model and the observations reduce from 11 cm to 1.3 cm.

顾及系统噪声和观测噪声的分级自适应信息滤波算法

高精度的载体动态导航与定位不仅需要对载体异常扰动和观测异常有良好控制,还需要对状态方程系统噪声及观测噪声的时变特性有准确认识和处理。首先针对包含系统噪声的动力学模型和包含时变观测噪声的导航系统,提出一种基于信息滤波形式的分级自适应滤波算法。然后针对系统噪声的渐变性和突变性,增加了遗忘因子和二段自适应因子,提高了对突变噪声估计的稳定性;顾及观测噪声的时变特性,采用传感器间差分和观测数据历元差分法估计观测噪声协方差。最后进行了仿真实验和深海拖体实验,结果表明,该算法不仅可以有效地估计系统噪声,还能准确地估计时变观测噪声的协方差阵,提高水下载体动态参数的估计精度。

Three-Step Difference Scheme for Solving Nonlinear Time-Evolution Partial Differential Equations

In this paper, a special three-step difference scheme is applied to the solution of nonlinear time-evolution equations, whose coefficients are determined according to accuracy constraints, necessary conditions of square conservation, and historical observation information under the linear supposition. As in the linear case, the schemes also have obvious superiority in overall performance in the nonlinear case compared with traditional finite difference schemes, e.g., the leapfrog(LF) scheme and the complete square conservation difference(CSCD) scheme that do not use historical observations in determining their coefficients, and the retrospective time integration(RTI) scheme that does not consider compatibility and square conservation. Ideal numerical experiments using the one-dimensional nonlinear advection equation with an exact solution show that this three-step scheme minimizes its root mean square error(RMSE) during the first 2500 integration steps when no shock waves occur in the exact solution, while the RTI scheme outperforms the LF scheme and CSCD scheme only in the first 1000 steps and then becomes the worst in terms of RMSE up to the 2500th step. It is concluded that reasonable consideration of accuracy, square conservation, and historical observations is also critical for good performance of a finite difference scheme for solving nonlinear equations.

多模GNSS精密卫星钟差估计与分析

对基于历元间差分相位和非差伪距观测值的混合差分卫星钟差估计方法进行了改进,实现了多模全球导航卫星系统（Global Navigation Satellite System,GNSS）卫星钟差联合快速估计。选择了全球分布的50个跟踪站进行实验,对卫星钟差精度进行了分析和精密单点定位（Precise Point Positioning,PPP）验证。结果表明：多模卫星钟差与武汉大学提供的最终精密卫星钟差互差优于0.2ns,精密单点定位结果与武汉大学发布的最终精密卫星轨道和钟差产品的定位精度相当。

Relative position determination of a lunar rover using the biased differential phase delay of same-beam VLBI

When only data transmission signals with a bandwidth of 1 MHz exist in the rover, the position can be obtained using the differential group delay data of the same-beam very long baseline interferometry (VLBI). The relative position between a lunar rover and a lander can be determined with an error of several hundreds of meters. When the guidance information of the rover is used to determine relative position, the rover's wheel skid behavior and integral movement may influence the accuracy of the determined position. This paper proposes a new method for accurately determining relative position. The differential group delay and biased differential phase delay are obtained from the same-beam VLBI observation, while the modified biased differential phase delay is obtained using the statistic mean value of the differential group delay and the biased phase delay as basis. The small bias in the modified biased phase delay is estimated together with other parameters when the relative position of the rover is calculated. The effectiveness of the proposed method is confirmed using the same-beam VLBI observation data of SELENE. The radio sources onboard the rover and the lander are designed for same-beam VLBI observations. The results of the simulations of the differential delay of the same-beam VLBI observation between the rover and the lander show that the differential delay is sensitive to relative position. An approach to solving the relative position and a strategy for tracking are also introduced. When the lunar topography data near the rover are used and the observations are scheduled properly, the determined relative position of the rover may be nearly as accurate as that solved using differential phase delay data.

An effective genetic algorithm to VDA with discontinuous “on-off” switches

With more and more improvements of atmosphere or ocean models,a growing number of physical processes in the form of parameterization are incorporated into the models,which,on the one hand,makes the models capable of describing the at-mospheric or oceanic movement more precisely,and on the other hand,introduces non-smoothness in the form of "on-off" switches into the models."On-off" switches enhance the nonlinearity of the models and finally result in the loss of the effec-tiveness of variational data assimilation(VDA) based on the conventional adjoint method(ADJ).This study,in virtue of the optimization ability of a genetic algorithm(GA) for non-smooth problems,presents a new GA(referred to as GA NEW) to solve the problems of the VDA with discontinuous "on-off" processes.In the GA-NEW,adaptive selection and mutation oper-ators,blend crossover operator,and elitist strategy are combined in application.In order to verify the effectiveness and feasi-bility of the GA NEW in VDA,an idealized model of partial differential equation with discontinuous "on-off" switches in the forcing term is adopted as the governing equation.By comparison with the ADJ,it is shown that the GA NEW in VDA is more effective and can yield better assimilation retrievals.In addition,VDA experiments demonstrate that the performance of a GA is greatly related to the configuration of genetic operators(selection,crossover and mutation operators) and much better results may be attained with more proper genetic operations.Furthermore,the robustness of the GA NEW to observational noise,model errors and observation density is investigated,and the results show that the GA NEW has stronger robustness than the ADJ with respect to all the three observation noises,model errors,and sparse observation.

Combining GPS carrier phase and Doppler observations for precise velocity determination

The truncation error and propagation error are analyzed for velocity determination through differential GPS carrier phase observations,and an approach for the choice of the best number of points for the central difference method is developed.In order to overcome the disadvantages of existing GPS velocity determination methods,a new velocity determination algorithm is presented,based on combining carrier phase and Doppler observations.The basic idea is that two types of observation are combined by adding their normal equations,and their weights are evaluated by strict Helmet variance-components estimation.In order to control the influence of outliers,a bifactor equivalent weights strategy is adopted.To validate this method,GPS data of the airborne gravimetry campaign MEXAGE2001 is tested.The results show that the precision and reliability of velocity determination are obviously improved by using the proposed method.