火星探测器行星际定轨两种数据处理方案比较

计算了由于形状、姿态和表面性质不准确导致火星探测器行星际定轨存在较大光压模型误差时,两种不同定轨方案(方案1只估计光压系数,方案2同时估计光压系数和随机加速度)对光压模型误差的补偿效果.在方案2中建立了高斯马尔科夫模型表征光压模型导致的加速度误差,并选取了合适的随机模型参数.仿真分析表明方案2可以有效补偿光压模型误差,...     

伪随机脉冲估计及其在简化动力学定轨中的应用

研究了简化动力学定轨方法中伪随机脉冲的定义、特征及估计的数学模型。结合CHAMP星栽GPS实测数据，讨论了不同力学模型及观测值情况下的随机脉冲的估计，并分析了随机脉冲在不同情形下的大小变化及其对定轨精度的调节作用。结果表明，随机脉冲的大小和使用的力学模型、是否估计经验参数及使用的观测值精度有关系。在力学模型误差较大的情况下，随机脉冲的设置能有效地补偿和吸收模型误差，从而提高定轨精度。     

低轨卫星精密定轨中重力场模型误差的补偿

分析了不同重力场对低轨卫星运动影响的特征，并基于CHAMP卫星和GRACE卫星的真实轨道，利用轨道积分和轨道拟舍的方法，研究了线性分段加速度、周期性分段加速度以厦虚拟随机脉冲加速度在精密定轨中对重力场模型误差的补偿效果。     

BERNESE光压模型参数的统计分析

BERNESE Extended CODE Orbit Model(ECOM)光压模型是GPS精密定轨中广泛采用的一种光压模型,本文首先介绍了该光压模型构造,并分析了该模型对三种不同类型GPS卫星的适用性。为定性了解ECOM光压模型中各参数对精密定轨的影响,采用附加参数统计检验方法对九个模型参数定性进行了评价。本文结果说明,采用ECOM模型时,实际估计八个参数较为合理。     

经验加速度补偿对HY-2A卫星精密定轨的影响

针对HY-2A卫星定轨中存在系统误差的问题,该文提出了加入经验加速度补偿系统误差。为了获得HY-2A卫星的高精度轨道,采用星载DORIS距离变率数据探索了经验加速度对定轨精度的影响。探讨了1d、3d和7d作为经验加速度周期的定轨精度差异,分析了3d作为经验加速度周期时在径向、法向和切向3个方向设置经验加速度对定轨精度的不同影响。研究结果表明:HY-2A卫星在径向和切向不存在系统误差,而在法向存在系统误差,因而在法向设置经验加速度进行力学模型补偿能够取得较好的定轨结果;3d作为经验加速度的补偿周期较为合适,不仅能够减少解算参数个数,缩短计算时间,而且径向定轨精度可达到1.00cm,满足HY-2A卫星精密定轨需求。     

北斗三号卫星经验型太阳光压模型分析与精化

太阳光压摄动作为在轨导航卫星受到的最大的非保守力,是卫星精密定轨的重要误差源。ECOM模型、ECOM2模型,这两种经验型光压模型被广泛应用于导航卫星定轨。然而,ECOM模型和ECOM2模型分别是针对GPS和GLONASS卫星设计的,并不完全适用于我国北斗三号(BDS-3)卫星。针对五参数ECOM模型在BDS-3卫星低太阳高度角时期轨道不连续性增大的问题,本文提出在 D方向引入一阶周期项来吸收未被模型化光压加速度。结果表明,引入一阶余弦周期项 D_c,能将低太阳高度角时期CAST卫星的切向、法向、径向重叠轨道误差分别减小约60%、52%、29%。针对ECOM2模型中 D_2c和 D₀、D_2s和 B_s之间存在的强相关性,本文提出了不估计 D_2c参数的八参数ECOM2模型和不估计 D_2c与 D_2s的七参数ECOM2模型。结果表明,相较九参数ECOM2模型,不估计 D_2c参数的八参数ECOM2模型能够将CAST卫星和SECM卫星径向重叠轨道误差分别减少约18%和27%。在此基础上,继续移除 D_2s后(七参数ECOM2),径向重叠轨道误差可进一步减小5.2%~8.5%。综合考察重叠轨道精度和SLR检核精度,不顾及 D_2c和 D_2s的七参数ECOM2模型表现最佳。CAST卫星和SECM卫星重叠轨道切向、法向、径向精度分别为5.0、3.4、1.4 cm和5.4、3.5、1.5 cm;SLR检核残差标准差分别为3.1~3.2 cm、4.4~4.7 cm。     

不同经验太阳光压模型对于北斗卫星定轨的适用性分析

当前的北斗卫星导航系统尚缺乏合适的太阳光压模型,由GPS的ECOM模型衍生而来的多种经验光压模型常被用于北斗定轨中。从观测值残差、轨道内、外符精度以及外推精度等方面比较分析了目前常用的4种经验光压模型对于北斗卫星定轨的适用性。结果表明,不同(类型)卫星适用不同的经验光压模型,但总体来看,9参数模型的适用性最差,而5参数和7参数模型的适用性相对较好。     

基于加速度数据的GPS定轨

未来的空间重力任务都会配备一台或者更多的加速度计。为了合理使用这些观测值,在数据处理之前加速度应对测量予以校正。本文中用加速度数据替代大气阻力和光压等非万有引力模型进行GPS精密定轨中。文中仍然使用经验加速度数据以弥补保守力模型的缺陷,并用经在轨校正的加速度观测值验证利用力模型确定的加速度。沿轨方向的符合程度较好。在太阳活动的高峰期,加入加速度数据的优势是非常明显的。模型化的加速度和经验加速度不能提供在此期间观测数据的高频扰动。处理了GRACE和CHAMP的长期观测数据。GRACE的平均轨道与高质量的JPL参考轨道在几厘米的程度上是符合的,比使用力模型的结果好,利用SLR的残差分析也可以得出这一结论。使用这种技术确定的每天的校正因子有微小的变化。估计过程中不包括经验加速度时,径向和法向的校正因子离散程度较大,轨道符合在分米级水平。     

新太阳光压模型在GNSS定轨中的应用

太阳光压摄动是影响卫星定轨中重要的误差源,在GNSS导航卫星精密定轨过程中使用最为广泛的光压模型为ECOM模型。为了探究几种ECOM模型及其适用性,该文以超快速星历为起算轨道,分析对比经典ECOM-1模型与最新13参数ECOMC模型对GPS/BDS卫星轨道的影响。结果显示:相较于ECOM-1模型,ECOMC模型在GPS定轨中精度有所提升,特别体现在径向精度提升,单天与三天弧段在径向的解算精度分别提升了12.73%和24.74%;在BDS定轨中,采用ECOMC模型,部分GEO卫星在径向方向单天精度有12.38%的提升,而对于IGSO与MEO卫星二者精度差异不大;分析可得,由于星体结构不对称引起卫星在沿太阳-卫星方向作用的偶数阶短周期谐波扰动,引入卫星-太阳方向偶数阶项的参数估计可提升卫星径向精度。     

基本导航模式下BDS-3卫星地影期间的定轨精度分析

2015年以来陆续发射入轨的北斗全球卫星导航系统(简称北斗三号系统,BeiDou global navigation satellite system,BDS-3)卫星,其姿态控制增加了连续动态偏置模式,为研究BDS-3卫星在地影期间的定轨精度提供了条件。首先利用ECOM (empirical CODE(Center for Orbit Determination in Europe) orbit model)系列模型评估了BDS-3卫星的光压摄动建模精度和定轨精度,同时以轨道重叠弧段精度、用户等效距离误差(user equivalent range error,UERE)、卫星激光测距(satellite laser ranging, SLR)残差和定位精度为指标,对基本导航模式下BDS-3卫星的定轨精度进行了评估。然后基于北斗60余天的实测数据进行了实验,结果表明,BDS-3卫星克服了区域系统卫星在姿态控制模式转换期间定轨精度下降的问题,其定轨精度与动态偏置期间定轨和预报精度相当,仅下降2～3 cm,定位精度下降1 cm,这与目前北斗的定轨精度和定位精度相比,可以忽略。进一步的分析表明,采用ECOM 5参数光压模型,连续动偏期间的轨道重叠弧段精度为0.26 m,预报2 h的UERE均方根降低至1.22 m,SLR残差的均方根小于0.31 m,大大提升了北斗系统的可用性。     

Evaluation of GPS orbit prediction strategies for the IGS Ultra-rapid products

The International GNSS Service (IGS) provides Ultra-rapid GPS & GLONASS orbits every 6 h. Each product is composed of 24 h of observed orbits with predicted orbits for the next 24 h. We have studied how the orbit prediction performance varies as a function of the arc length of the fitted observed orbits and the parameterization strategy used to estimate the empirical solar radiation pressure (SRP) effects. To focus on the dynamical aspects of the problem, nearly ideal conditions have been adopted by using IGS Rapid orbits and known earth rotation parameters (ERPs) as observations. Performance was gauged by comparison with Rapid orbits as truth by examining WRMS and median orbit differences over the first 6-h and the full 24-h prediction intervals, as well as the stability of the Helmert frame alignment parameters. Two versions of the extended SRP orbit model developed by the Centre for Orbit Determination in Europe (CODE) were tested. Adjusting all nine SRPs (offsets plus once-per-revolution sines and cosines in each satellite-centered frame direction) for each satellite shows smaller mean sub-daily, scale, and origin translation differences. On the other hand, eliminating the four once-per-revolution SRP parameters in the sun-ward and the solar panel axis directions yields orbit predictions that are much more rotationally stable. We found that observed arc lengths of 40–45 h produce the most stable and accurate predictions during 2010. A combined strategy of rotationally aligning the 9 SRP results to the 5 SRP frame should give optimal predictions with about 13 mm mean WRMS residuals over the first 6 h and 50 mm over 24 h. Actual Ultra-rapid performance will be degraded due to the unavoidable rotational errors from ERP predictions.     

相位解缠的CKF局部多项式系数递推估计法

为从含噪干涉相位数据中估计出解缠相位,本文提出相位解缠的CKF局部多项式系数递推估计法。利用基于修正矩阵束模型的局部相位梯度估计算法(AMPM)来获取多项式系数中的梯度信息,在此基础上获得局部多项式系数初始值(即状态变量初值),最后利用容积卡尔曼滤波(CKF)算法递推估计多项式系数状态估计值,从而获得解缠相位。可根据干涉图条纹密度以及相位噪声情况,分别采用逐行(或逐列)扫描方式或质量图引导策略引导容积卡尔曼滤波器解缠干涉图缠绕像元。模拟样例与实测数据试验结果表明,与其他同类方法相比,本文算法能从噪声干涉图中获得更高的解缠精度。     

Using external tropospheric corrections to improve GNSS positioning of hot-air balloon

High accurate global navigation satellite systems (GNSS) require to correct a signal delay caused by the troposphere. The delay can be estimated along with other unknowns or introduced from external models. We assess the impact of the recently developed augmentation tropospheric model on real-time kinematic precise point positioning (PPP). The model is based on numerical weather forecast and thus reflects the actual state of weather conditions. Using the G-Nut/Geb software, we processed GNSS and meteorological data collected during the experiment using a hot-air balloon flying up to an altitude of 2000 m. We studied the impacts of random walk noise setting of zenith total delay (ZTD) on estimated parameters and the mutual correlations, the use of external tropospheric corrections, the use of data from a single or dual GNSS constellation and the use of Kalman filter and backward smoothing processing methods. We observed a significant negative correlation of the estimated rover height and ZTD which depends on constraining ZTD estimates. Such correlation caused a degraded performance of both parameters when estimated simultaneously, in particular for a single GNSS constellation. The impact of ZTD constraining reached up to 50-cm differences in the rover height. Introducing external tropospheric corrections improved the PPP solution regarding: (1) shortened convergence, (2) better overall robustness, particularly, in case of degraded satellite geometry, (3) less adjusted parameters with lower correlations. The numerical weather model-driven PPP resulted in 9–12- and 5–6-cm uncertainties in the rover altitude using the Kalman filter and the backward smoothing, respectively. Compared to standard PPP, it indicates better performance by a factor of 1–2 depending on the availability of GNSS constellations, the troposphere constraining and the processing strategy.     

CODE’s five-system orbit and clock solution—the challenges of multi-GNSS data analysis

This article describes the processing strategy and the validation results of CODE’s MGEX (COM) orbit and satellite clock solution, including the satellite systems GPS, GLONASS, Galileo, BeiDou, and QZSS. The validation with orbit misclosures and SLR residuals shows that the orbits of the new systems Galileo, BeiDou, and QZSS are affected by modelling deficiencies with impact on the orbit scale (e.g., antenna calibration, Earth albedo, and transmitter antenna thrust). Another weakness is the attitude and solar radiation pressure (SRP) modelling of satellites moving in the orbit normal mode—which is not yet correctly considered in the COM solution. Due to these issues, we consider the current state COM solution as preliminary. We, however, use the long-time series of COM products for identifying the challenges and for the assessment of model-improvements. The latter is demonstrated on the example of the solar radiation pressure (SRP) model, which has been replaced by a more generalized model. The SLR validation shows that the new SRP model significantly improves the orbit determination of Galileo and QZSS satellites at times when the satellite’s attitude is maintained by yaw-steering. The impact of this orbit improvement is also visible in the estimated satellite clocks—demonstrating the potential use of the new generation satellite clocks for orbit validation. Finally, we point out further challenges and open issues affecting multi-GNSS data processing that deserves dedicated studies.     

北斗卫星太阳光压解析模型建立及应用

光压模型是导航卫星高精度定轨、定位的基础。目前关于北斗卫星光压摄动模型的研究并不少见,但基于卫星物理参数的综合解析模型建立与应用公开可见的论述并不多见。不同于其他保守和非保守摄动力,光压辐射与卫星本身参数状态密切相关,具有明显的个体差异性。本文基于光压辐射的物理机理、北斗卫星物理参数、姿态控制模式等,建立光压摄动综合解析模型,以精密星历和激光测距数据为基准,验证了综合解析模型能够获得分米级的精密定轨精度。在此基础上,根据卫星角动量守恒和在轨遥测参数变化,分析了综合解析模型和在轨实际干扰力的差值,提出了在综合解析模型基础上增加常数经验修正项Da、Ya的方法,以北斗C08、C10星为例,分别可获得0.078、0.084 m的SLR检核精度,相比于利用CODE经验改进模型,精度分别提高0.021、0.045 m。     

基于正则化的地表反射特性参数反演方法

区域和全球尺度下研究气候变化,需要准确描述大气边界层处下垫面地表的光反射特性。为此,提出基于正则化的约束反演方法,其核心在于正则化参数的选取。通过L曲线拐点位置的确定,求出最合适的正则化约束参数,以稳定陆表反射特性参数的定量反演。京津唐地区数值反演试验与熵减分析结果表明,可见光红通道和近红外通道的信息指数分别为11.682 2和10.072 6;基于L曲线的地物反射特性正则化反演前后,两个通道的平均信息指数增量分别为0.440 0和0.354 6,最大增量为2.467 2和2.290 5。L曲线正则化方法的优势在于其不依赖于地表参数的先验知识,可有效解决卫星观测信息不足时地表参数的反演问题。     

一种无须变换参考星的GNSS单基线卡尔曼滤波算法

处理单基线全球导航卫星系统观测数据可获取位置、时间、大气延迟等信息,其应用包括相对定位、时频传递等。为实现实时性,常采用卡尔曼滤波递归地估计各类参数;为确保可靠性,还需形成一组独立的双差模糊度,并将其正确地固定为整数。实践中,滤波函数模型较常采用双差观测方程(即双差滤波模型)。若在当前历元原先的参考星不再可视时,双差滤波模型则需要定义新的参考星,并"映射"双差模糊度预报值以确保滤波连续。此外,双差滤波模型所计算的接收机相位钟差估值吸收了对应于参考星的站间单差模糊度,因此当参考星变换后可能会发生"整周跳跃"。在仍将双差模糊度作为一类可估参数的前提下,本文推导出以站间单差观测方程为滤波函数模型的算法(单差滤波模型),并证明了其与双差滤波模型具备理论上的等价性和实施上的差异性。与双差滤波模型相比,单差滤波模型不再需要"映射"双差模糊度预报值等运算,从而具备了更高的计算效率和灵活性;单差滤波模型所提供的接收机相位钟差估值也不受"整周跳跃"的影响,因此特别有利于频率传递应用。     

Systematic biases in DORIS-derived geocenter time series related to solar radiation pressure mis-modeling

As any satellite geodesy technique, DORIS can monitor geocenter variations associated to mass changes within the Earth–Atmosphere–Continental hydrosphere–Oceans system. However, especially for the Z-component, corresponding to a translation of the Earth along its rotation axis, the estimated geocenter is usually affected by large systematic errors of unknown cause. By reprocessing old DORIS data, and by analyzing single satellite solutions in the frequency domain, we show that some of these errors are satellite-dependent and related to the current DORIS orbit determination strategy. In particular, a better handling of solar pressure radiation effects on SPOT-2 and TOPEX satellites is proposed which removes a large part of such artifacts. By empirically multiplying the current solar pressure model with a single coefficient (1.03 for TOPEX/Poseidon after 1993.57, and 0.96 before; and 1.08 for SPOT-2) estimated over a long time period, we can improve the measurement noise of the Z-geocenter component from 47.5 to 30.4 mm for the RMS and from 35 to 6 mm for the amplitude of the annual signal. However, the estimated SRP coefficient for SPOT-2 presents greater temporal variability, indicating that a new, dedicated solar radiation pressure model is still needed for precise geodetic applications. In addition, for the TOPEX satellite, a clear discontinuity of unknown cause is also detected on July 27, 1993.