改进CODE GIM的GNSS广播电离层模型评估方法

针对如何有效地对各类电离层模型在建模实现、模型精度、模型时效性等方面进行综合评估问题,该文提出一种基于改进CODE模型(CODE+模型)全球电离层图(GIM)的预报电离层精度评估方法,通过增加我国陆态网监测站数据,提高我国及周边地区的电离层建模精度,弥补了CODE GIM在我国及周边地区因观测数据少而精度受限的不足。通过试验分析表明,改进CODE GIM能够满足精度要求,且更好地与我国实际电离层情况相吻合;并以此为基准评估GNSS广播电离层精度,对比分析了GPS、BDS、Galileo电离层模型的精度,得到一些初步结论。     

GNSS data management and processing with the GPSTk

We organize complex problems in simple ways using a GNSS data management strategy based on “GNSS Data Structures” (GDS), coupled with the open source “GPS Toolkit” (GPSTk) suite. The code resulting from using the GDS and their associated “processing paradigm” is remarkably compact and easy to follow, yielding better code maintainability. Furthermore, the data abstraction allows flexible handling of concepts beyond mere data encapsulation, including programmable general solvers. An existing GPSTk class can be modified to achieve the goal. We briefly describe the “GDS paradigm” and show how the different GNSS data processing “objects” may be combined in a flexible way to develop data processing strategies such as Precise Point Positioning (PPP) and network-based PPP that computes satellite clock offsets on-the-fly.     

Reliability checking for GNSS baseline and network processing

Reliability analysis is inseparably connected with the formulation of failure scenarios, and common test statistics are based on specific assumptions. This is easily overlooked when processing observation differences. Poor failure identification performance and misleading pre-analysis results, mainly meaningless minimum detectable biases and external reliability measures, are the consequence. A reasonable failure scenario for use with differenced GNSS observations is formulated which takes into account that individual outliers in the original data affect more than one processed observation. The proper test statistics and reliability indicators are given for use with correlated observations and both batch processing and Kalman filtering. It is also shown that standardized residuals and redundancy numbers fail completely when used with double differenced observations.

GNSS非模型化误差处理理论与方法

正由于系统误差的时空复杂特性及认知有限,即使通过了差分和线性组合、经验模型改正及传统参数化吸收等方式,在GNSS观测值中仍然会有残余系统误差的存在,这些残余系统误差可称为非模型化误差。非模型化误差会对GNSS精密定位与导航产生负面作用。为突破现有GNSS应用的精度和可靠性,本文研究了GNSS非模型化误差的处理理论与方法,包括不同应用模式和观测环境下的处理策略,并建立随外界条件变化而自适应调整的非模型化误差处理流程。     

GNSS卫星精密定轨综述:现状、挑战与机遇

GNSS卫星精密轨道是高精度GNSS应用的基础与前提,GNSS卫星精密定轨技术也一直都是卫星导航领域的研究重点与热点。本文首先介绍了GNSS星座与跟踪数据概况,梳理了精密定轨函数模型、动力学模型及随机模型构建过程中的关键问题,归纳了低轨星载观测和星间链路观测等多源数据增强GNSS精密定轨的研究进展;然后,从应用的角度总结了当前GNSS精密轨道产品的基本状态,并进行了精度评估;最后,讨论了GNSS精密定轨在大网快速解算、多层次观测数据融合、太阳光压模型精化及高精度实时定轨等方面所面临的挑战,并展望了低轨星座、光钟、激光链路等新技术给GNSS精密定轨带来的机遇。     

Improved network-based single-epoch ambiguity resolution using centralized GNSS network processing

Network real-time kinematic (NRTK) positioning is today’s industry standard for high-precision applications. Once network ambiguities are fixed, the network engine processes simultaneous observations from a number of continuously operating reference stations to compute corrections for users operating within the network area. Users are treated as passive nodes of the network. However, if two-way communication is available, then users could transmit their observations to the central processing facility where the network can treat them as active nodes, densifying the existing network infrastructure. This multiple rover network (MRN) concept exploits the additional information provided by users in a GNSS network. One application is to use the shorter inter-receiver distances to improve the success rate of single-epoch ambiguity resolution. This is also the goal of the subset ambiguity resolution algorithm, which improves the single-epoch success rate by allowing a subset of ambiguities to be resolved. We present an enhanced processing strategy to complement centimeter-level single-epoch NRTK positioning. This approach combines a single-baseline and an MRN solution with the partial ambiguity resolution algorithm and is only possible for a centralized GNSS network architecture. The algorithm is tested against the standard network ambiguity resolution strategy of full-set ambiguity fixing with respect to the nearest reference station. A 24-h dataset from the Southern California Integrated GNSS network is used with a configuration of three reference stations and four users. The enhanced solution achieves a mean ambiguity resolution success rate of 83% over all four users and all epochs, compared to 32% for the conventional technique.     

GNSS非差非组合数据处理与PPP-RTK高精度定位

本文首先回顾了GNSS差分和组合数据处理的起源、特点和应用,并阐述了其在多频多模背景下的局限。然后,引出了非差非组合数据处理的诸多优势,介绍了构建满秩非差非组合函数模型的消秩亏方法。基于该方法,本文系统构建了系列非差非组合PPP-RTK模型,包括伪距加相位和仅用相位两大类。两类模型均考虑不同的大气约束而衍生出电离层加权、浮点和固定3种变体,且所有模型均顾及码分多址和频分多址两类系统。最后,本文测试分析了非差非组合PPP-RTK在无人船、无人机和农机应用中的动态定位性能。试验结果表明,3个场景下的模糊度首次固定时间均在10 s以内,模糊度固定成功率在96%以上,水平定位精度优于2 cm,高程定位精度优于5 cm。在Galileo+GPS+BDS三系统农机定位中,仅用相位PPP-RTK与伪距加相位PPP-RTK定位性能相当。与Galileo+GPS双系统定位相比,三系统PPP-RTK将模糊度首次固定时间从几百秒缩短至几秒,模糊度固定成功率从85%左右提升至99%以上,定位精度提升了30%左右。     

An enhanced strategy for GNSS data processing of massive networks

Although the computational burden of global navigation satellite systems (GNSS) data processing is nowadays already a big challenge, especially for huge networks, integrated processing of denser networks with data of multi-GNSS and multi-frequency is desired in the expectation of more accurate and reliable products. Based on the concept of carrier range, in this study, the precise point positioning with integer ambiguity resolution is engaged to obtain the integer ambiguities for converting carrier phases to carrier ranges. With such carrier ranges and pseudo-ranges, rigorous integrated processing is realized computational efficiently for the orbit and clock estimation using massive networks. The strategy is validated in terms of computational efficiency and product quality using data of the IGS network with about 460 stations. The experimental validation shows that the computation time of the new strategy increases gradually with the number of stations. It takes about 14 min for precise orbit and clock determination with 460 stations, while the current strategy needs about 82 min. The overlapping orbit RMS is reduced from 27.6 mm with 100 stations to 24.8 mm using the proposed strategy, and the RMS could be further reduced to 23.2 mm by including all 460 stations. Therefore, the new strategy could be applied to massive networks of multi-GNSS and multi-frequency receivers and possibly to achieve GNSS data products of higher quality.     

(Near-)real-time orbit determination for GNSS radio occultation processing

The processing of GPS radio occultation measurements for use in numerical weather predictions requires a precise orbit determination (POD) of the host satellite in near-real-time. Making use of data from the GRAS instrument on Metop-A, the performance of different GPS ephemeris products and processing concepts for near-real-time and real-time POD is compared. While previous analyses have focused on the achievable along-track velocity accuracy, this study contributes a systematic comparison of the resulting estimated bending angles. This enables a more rigorous trade-off of different orbit determination methodologies in relation to the end-user needs for atmospheric science products. It is demonstrated that near-real-time GPS orbit and clock products have reached a sufficient quality to determine the Metop-A along-track velocity with an accuracy of better than 0.05 mm/s that was formerly only accessible in post-processing. The resulting bending angles are shown to exhibit standard deviation and bias differences of less than 0.3 % compared with post-processed products up to altitudes of at least 40 km, which is notably better than 1 % accuracy typically assumed for numerical weather predictions in this height regime. Complementary to the analysis of ground-based processing schemes, the potential of autonomous on-board orbit determination is investigated for the first time. Using actual GRAS flight data, it is shown that a 0.5 m 3D rms position accuracy and a 0.2 mm/s along-track velocity accuracy can in fact be obtained in real-time with the currently available GPS broadcast ephemeris quality. Bending angles derived from the simulated real-time processing exhibit a minor performance degradation above tangent point heights of 40 km but negligible differences with respect to ground-based products below this altitude. Onboard orbit determination and, if desired, bending angle computation, can thus enable a further simplification of the ground segment in future radio occultation missions and contribute to reduced product latencies for radio occultation data assimilation in numerical weather predictions.     

云南及周边地区GNSS数据处理方法优化

采用麻省理工学院开发的GAMIT／GLOBK软件,将2015年-2016年全球347个IGS站观测数据分七个子网解算,得到一个固定的参考框架来解算云南及周边地区的35个全球卫星导航系统（GNSS）基准站的坐标,测站坐标均方根误差水平方向在0.7 mm以内,垂直方向在0.3 mm以内,水平方向的坐标重复性精度在5 mm以内,垂向坐标的重复性精度大多数在2.5 cm以内;与在ITRF2014下解算的测站坐标、基线长度、水平速度场结果对比表明:测站坐标存在系统误差,水平方向上的差异在8.5 mm以内,垂直方向上在3 cm以内;基线长度差异在2 mm以内,水平速度场在数值上存在毫米级的差异,方向上基本一致．      

Analysis of the first year of Earth rotation parameters with a sub-daily resolution gained at the CODE processing center of the IGS

 The solutions of the CODE Analysis Center submitted to the IGS, the International Global Position System (GPS) Service for Geodynamics, are based on three days of observation of about 80–100 stations of the IGS network. The Earth rotation parameters (ERPs) are assumed to vary linearly over the three days with respect to an a priori model. Continuity at the day boundaries as well as the continuity of the first derivatives are enforced by constraints. Since early April 1995 CODE has calculated a new ERP series with an increased time resolution of 2 hours. Again continuity is enforced at the 2-hours-interval boundaries. The analysis method is described, particularly how to deal with retrograde diurnal terms in the ERP series which may not be estimated with satellite geodetic methods. The results obtained from the first year of data covered by the time series (time interval from 4 April 1995 to 30 June 1996) are also discussed. The series is relatively homogeneous in the sense of the used orbit model and the a priori model for the ERPs. The largest source of excitation at daily and sub-daily periods is likely to be the effect of the ocean tides. There is good agreement between the present results and Topex/Poseidon ocean tide models, as well as with models based on Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) data. Non-oceanic periodic variations are also observed in the series. Their origin is most probably a consequence of the GPS solution strategy; other possible sources are the atmospheric tides. Received: 13 July 1999 / Accepted: 21 March 2000     

Assessment of local GNSS baselines at co-location sites

As one of the major contributors to the realisation of the International Terrestrial Reference System (ITRS), the Global Navigation Satellite Systems (GNSS) are prone to suffer from irregularities and discontinuities in time series. While often associated with hardware/software changes and the influence of the local environment, these discrepancies constitute a major threat for ITRS realisations. Co-located GNSS at fundamental sites, with two or more available instruments, provide the opportunity to mitigate their influence while improving the accuracy of estimated positions by examining data breaks, local biases, deformations, time-dependent variations and the comparison of GNSS baselines with existing local tie measurements. With the use of co-located GNSS data from a subset sites of the International GNSS Service network, this paper discusses a global multi-year analysis with the aim of delivering homogeneous time series of coordinates to analyse system-specific error sources in the local baselines. Results based on the comparison of different GNSS-based solutions with the local survey ties show discrepancies of up to 10 mm despite GNSS coordinate repeatabilities at the sub-mm level. The discrepancies are especially large for the solutions using the ionosphere-free linear combination and estimating tropospheric zenith delays, thus corresponding to the processing strategy used for global solutions. Snow on the antennas causes further problems and seasonal variations of the station coordinates. These demonstrate the need for a permanent high-quality monitoring of the effects present in the short GNSS baselines at fundamental sites.     

GNSS在线数据处理系统在工程控制网中的应用与分析

介绍目前几个主要的GNSS在线数据处理系统,着重利用其中5个GNSS在线数据处理系统对某工程控制网的观测数据进行多个方案的处理;对处理结果进行对比分析,检验其内符合精度;再利用框架和历元转换理论和方法,将多个系统处理获得的不同ITRF框架下2011即时历元的观测点坐标转换归算到CGCS2000坐标下进行对比,结果表明:GNSS在线数据处理系统完全能够满足工程控制网的数据处理、精度要求以及成果提交等需求。     

ITRF 2008与ITRF 2014的差异对GNSS数据处理的影响

针对全球导航卫星系统(GNSS)数据处理过程中旧的ITRF 2008参考框架现势性不足及新的ITRF2014框架在数据的数量与质量、参数模型、测站的分布合理性上均有提高等状况,该文以陆态网的最近两年的观测数据为例,对比分析了ITRF2008和ITRF2014框架下各测站的坐标、基线长度、水平速度场的差异,以期为当前高精度GNSS数据处理提供参考。实验表明:两个框架下的成果经基准转换后,测站在X、Y、Z方向的差异均为毫米级;基线差异平均在1 mm以内;水平速度场差值的最大值为5.75(mm·a~(-1)),最小值为-4.88(mm·a~(-1)),平均值为-0.45(mm·a~(-1)),方向上差值的平均值为0.02rad。目前两个框架的差异对一般工程应用基本上可以忽略,但对地震监测的陆态网来说,则必须考虑。     

基于CORS基准站的GNSS滑坡地质灾害监测数据处理策略分析

为充分发挥连续运行参考站(CORS)基准站在滑坡地质灾害监测领域的资源优势,分析了基于CORS基准站的变形监测数据处理策略,评估了观测值类型、解算时长、基线长度对监测精度的影响,给出了CORS基准站作为监测基准时可覆盖的范围,为推动CORS在变形监测的深度应用提供了重要的数据支撑.      

An investigation of GNSS atomic clock behavior at short time intervals

A technique for obtaining clock measurements from individual GNSS satellites at short time intervals is presented. The methodology developed in this study allows for accurate satellite clock stability analysis without an ultra-stable clock at the ground receiver. Variations in the carrier phase caused by the satellite clock are isolated using a combination of common GNSS carrier-phase processing techniques. Furthermore, the white phase variations caused by the thermal noise of the collection and processing equipment are statistically modeled and removed, allowing for analysis of clock performance at subsecond intervals. Allan deviation analyses of signals collected from GPS and GLONASS satellites reveal distinct intervals of clock noise for timescales less than 100 s. The clock data collected from GPS Block IIA, IIR, IIR-M, and GLONASS satellites reveal similar stability performance at time periods greater than 20 s. The GLONASS clock stability in the 0.6–10 s range, however, is significantly worse than GPS. Applications that rely on ultra-stable clock behavior from the GLONASS satellites at these timescales may therefore require high-rate corrections to estimate and remove oscillator-based errors in the carrier phase.     

Remote leveling of tide gauges using GNSS reflectometry: case study at Spring Bay,Australia

We further developed a new approach using GNSS reflectometry to determine the leveling connection between a tide gauge and a GNSS antenna. This approach includes the optimization of the unknown receiver bandwidth and the estimation of frequency changes in the signal-to-noise ratio (SNR) oscillation through an extended Kalman filter/smoother algorithm. We also corrected the geometric bending of the GNSS signals due to tropospheric refraction using local meteorological observations. Using 3 weeks of SNR data in Spring Bay, Australia, from a GNSS antenna placed sideways (i.e., ground plane orientated vertically and directed in azimuth toward the sea surface) to improve the SNR interference near the horizon, we obtained mean leveling differences of approximately 5 mm, with an RMS of approximately 3 cm level with respect to the nominal leveling from classical surveying techniques. SNR data from three different receiver manufacturers, coupled to the same antenna, provided similar leveling results. With a second antenna in the usual upright configuration, we obtained mean leveling differences of 1–2 cm and a RMS of about 10 cm. In the upright configuration, the leveling differences may include errors in the GNSS antenna phase center calibration, which are avoided in our technique but not in the classical surveying techniques. These results demonstrate the usefulness of the reflectometry technique to obtain precisely and remotely the leveling between a GNSS antenna and a tide gauge. In addition, this technique can be applied continuously, providing an independent and economical means to monitor the stability of the tide gauge zero.     

GNSS RTK技术下海洋平台桩腿动态变形监测及数据处理

海洋平台及其桩腿在长期使用中存在着波浪、海流、风荷载等环境激励作用下的动态响应。本文以海星达H32全能型GNSS RTK双频接收机为试验仪器,采用GPS+GLONASS+BDS三星系组合系统对位于渤海海域的埕岛油田某平台桩腿进行动态变形监测。结合Ensemble Empirical Mode Decomposition(EEMD)和Butterworth滤波方法的降噪特性,提出一种适用于海洋平台工作环境的新型混合滤波方法 MDB,并用Matlab软件编制的程序对GNSS RTK监测数据进行分析,得到桩腿测点的实时振动位移曲线。结果表明:GNSS RTK结合MDB滤波技术用于海洋平台桩腿动态变形监测是可行的;MDB滤波器能有效去除海洋平台振动信息的随机噪声和多路径误差;从去除多路径误差和随机噪声之后的海洋平台桩腿测点位移云图,可以非常清楚地看出桩腿在环境激励作用下水平方向产生的可逆位移轨迹,这对海洋平台结构健康监测、诊断和评估具有重要意义。