不同对流层改正方法对 PPP 定位效果影响的对比分析

对流层延迟是影响精密单点定位效果的一项重要误差源,不同的对流层改正方法直接影响PPP的定位结果。对比分析采用UNB3模型、Saastamoinen模型、ZTD参数估计3种方法对PPP定位精度和收敛时间的影响。实验结果表明:3种模型平面改正精度和收敛时间基本一致。天顶方向改正精度UNB3模型与ZTD参数估计法基本相当,但两者优于Saastamoinen模型;收敛速度UNB3模型与Saastamoinen模型基本一致,ZTD参数估计法收敛速度较慢。     

一种区域实时对流层内插模型及其在PPP中的应用

利用反距离加权内插法,对基准站解算的天顶对流层延迟（ZTD）建立了区域实时ZTD模型,评估了该模型内插流动站对流层延迟对PPP定位精度和收敛时间的影响。试验表明：与传统ZTD采用参数估计的处理方法对比,二者解算得到的PPP精度在水平方向上效果相当,但在垂直方向上,模型内插对流层解算的定位精度提高约为5 cm,且能显著提高PPP收敛速度。说明应用本方法建立非气象参数的区域天顶对流层延迟模型能有效加快PPP的收敛速度,且提高定位精度。     

海道测量定位中对流层延迟差分估计技术研究

为削弱海上对流层延迟对高精度海道测量的影响,提出了一种基于差分改正思想的对流层延迟估计方法。首先,以Saastamoinen模型作为先验值,采用精密单点定位技术估算对流层改正量。将天顶延迟的剩余误差作为待定参数,用Kalman滤波估计对流层的残余量;然后,分别估计基准站和移动站的对流层延迟,作为差分计算的初值代入差分解算模型中,从而求得海上移动站的精确位置。实测数据表明,相对于常规动态解,基于对流层差分改正的定位技术改善了移动站的定位精度,其中,垂直方向的精度提高了17.6%。     

对流层参数估计策略对PPP精度影响分析

精密单点定位(Precise Point Position,PPP)技术是当今卫星导航定位领域的研究热点。该技术能够在全球范围内快速获取高精度框架坐标。针对精密单点定位中对流层参数估计问题,提出单参数模型、分段常参数模型和附加随机漫步过程约束的分段常参数模型中对流层参数估计策略,选取10个全球IGS测站进行精密单点定位实验。结果表明:对流层改正主要影响U方向的定位精度,且3种对流层参数估计策略均能够使定位精度U方向优于0.020m;但不同的对流层参数估计策略对定位精度有一定差异,其中单参数模型与分段常参数模型相比,U方向定位精度最大差异超过0.015m,而附加随机漫步过程约束的分段常参数模型与分段常参数模型定位精度相当。     

GPS定位中的对流层模型分析

系统地分析对流层延迟特性在GPS导航中造成的定位误差,并主要介绍目前卫星定位领域主要应用的一些对流层折射修正模型。基于霍普尔德模型和萨斯塔莫宁模型,提出一种在缺少实测气象参数条件下,使用的简单对流层延迟修正模型。利用Matlab仿真软件对静态和动态接收机实测数据进行分析。结果表明,无气象参数的简单修正模型可以消除70％左右的对流层影响,有效地提高GPS的定位精度。     

精密单点定位中对流层延迟改正模型分析

在精密单点定位中,通过有效的方法减小对流层误差源对定位精度的影响。其中Saastamoinen模型和Niell模型对减小对流层延迟误差效果较好。重点介绍了这两种模型,并通过实验分析了两种模型在精密单点定位中对对流层延迟误差的改正效果。实验结果以标准偏差和均方根的形式给出,说明了Saastamoinen模型与Niell模型对定位结果都有所改善,但Niell模型结果较好。     

GPS反演可水量中的三种对流层延迟模型精度分析

利用GAMIT/GLOBK软件解算bjfs、shao、wuhn、twtf四个IGS站的数据,分别运用Hopfield、Saastamoinen、EGNOS模型,计算出测站shao的GPS大气可降水量,并结合气象数据,对三种不同对流层延迟模型在GPS探测大气可降水量中的精度进行了分析。结果表明,Saastamoinen模型的精度略高于Hopfield模型的精度,EGNOS模型精度好于Hopfield和Saastamoinen模型,但在气象条件变化剧烈时,其精度不如实测地面气象数据的Hopfield和Saastamoinen模型。     

天线相位中心改正模型对PPP参数估计的影响

比较了IGS发布的相对天线相位中心改正模型与绝对天线相位中心改正模型,分析了两种不同模型对精密单点定位（PPP）参数估计的影响。结果表明,采用不同的天线相位中心改正模型,天顶对流层延迟（ZPD）的估值存在5mm左右的差异,接收机钟差参数存在3ns左右的差异,估计的测站坐标高程方向有1cm左右的差异。使用绝对天线相位中心模型估计得到的ZPD精度优于5mm,高程方向定位精度约为1cm,接收机钟差估计的精度达0.1ns。     

卫星导航系统中对流层改正模型分析

为了获取高精度的卫星导航系统时间, 需要对卫星导航系统信号传输过程中的各项误差进行修正, 对流层延迟是卫星导航系统精密定位的主要误差源之一。本文利用模型函数理论针对对流层延迟的误差修正进行比对分析研究, 分别介绍了对流层模型:Marini模型、霍普菲尔德(Hopfield)模型、萨斯塔莫宁(Saastamoinen)模型、勃兰克(Black)模型, 定量分析了温度、气压、湿度等气象参数及测站地理位置对各模型的影响程度, 系统分析了对流层延迟特性及其误差改正模型的精度, 并利用事后公布的IGS跟踪站的对流层时延改正数据对模型分析结果进行检验, 得出Black模型受测站高程及各气象参数变化影响最小, 且优于GPS接收机内部改正模型产生的对流层时延。     

三种对流层延迟模型的精度对比

针对不同对流层延迟模型的改正精度不同的问题,该文采用3个IGS站BJFS、SHAO、WUHN的2014年对流层天顶总延迟数据以及地面气象数据,对目前常用的3种对流层延迟模型:霍普菲尔德(Hopfield)、萨斯塔莫宁(Saastamoinen)、欧洲地球静止导航重叠服务(EGNOS)的精度进行了分析。结果表明:Saastamoinen和Hopfield模型的精度相当,EGNOS模型精度略差于其余两种模型,但能满足GNSS米级的定位要求;在气象条件变化剧烈时,EGNOS模型精度不如实测地面气象数据的Hopfield和Saastamoinen模块。     

Improving BeiDou real-time precise point positioning with numerical weather models

Precise positioning with the current Chinese BeiDou Navigation Satellite System is proven to be of comparable accuracy to the Global Positioning System, which is at centimeter level for the horizontal components and sub-decimeter level for the vertical component. But the BeiDou precise point positioning (PPP) shows its limitation in requiring a relatively long convergence time. In this study, we develop a numerical weather model (NWM) augmented PPP processing algorithm to improve BeiDou precise positioning. Tropospheric delay parameters, i.e., zenith delays, mapping functions, and horizontal delay gradients, derived from short-range forecasts from the Global Forecast System of the National Centers for Environmental Prediction (NCEP) are applied into BeiDou real-time PPP. Observational data from stations that are capable of tracking the BeiDou constellation from the International GNSS Service (IGS) Multi-GNSS Experiments network are processed, with the introduced NWM-augmented PPP and the standard PPP processing. The accuracy of tropospheric delays derived from NCEP is assessed against with the IGS final tropospheric delay products. The positioning results show that an improvement in convergence time up to 60.0 and 66.7% for the east and vertical components, respectively, can be achieved with the NWM-augmented PPP solution compared to the standard PPP solutions, while only slight improvement in the solution convergence can be found for the north component. A positioning accuracy of 5.7 and 5.9 cm for the east component is achieved with the standard PPP that estimates gradients and the one that estimates no gradients, respectively, in comparison to 3.5 cm of the NWM-augmented PPP, showing an improvement of 38.6 and 40.1%. Compared to the accuracy of 3.7 and 4.1 cm for the north component derived from the two standard PPP solutions, the one of the NWM-augmented PPP solution is improved to 2.0 cm, by about 45.9 and 51.2%. The positioning accuracy for the up component improves from 11.4 and 13.2 cm with the two standard PPP solutions to 8.0 cm with the NWM-augmented PPP solution, an improvement of 29.8 and 39.4%, respectively.     

偏航姿态对北斗精密单点定位的影响分析

当太阳相对于卫星轨道面的高度角较小时,北斗导航卫星将不会跟踪太阳位置,卫星姿态发生异常复杂的变化后一段时间内处于零偏模式。在此期间采用名义姿态将影响卫星天线相位中心偏差、相位缠绕等误差计算,进而使精密单点定位(PPP)参数估计和天顶对流层延迟估计出现偏差。研究表明,在北斗导航卫星处于零偏期间,采用名义姿态计算的相位缠绕、天线相位中心偏差中存在超过15cm的误差。在此期间的北斗卫星采用零偏姿态改正相位缠绕等误差,与采用名义姿态相比,动态PPP位置参数N、E、U的估计精度可以提高53.2%、54.2%、39.3%,静态PPP位置参数N、E、U的估计精度可以提高61.0%、72.3%、58.4%,天顶对流层延迟估计精度提高33.0%。     

Modeling tropospheric wet delays with national GNSS reference network in China for BeiDou precise point positioning

During past decades, precise point positioning (PPP) has been proven to be a well-known positioning technique for centimeter or decimeter level accuracy. However, it needs long convergence time to get high-accuracy positioning, which limits the prospects of PPP, especially in real-time applications. It is expected that the PPP convergence time can be reduced by introducing high-quality external information, such as ionospheric or tropospheric corrections. In this study, several methods for tropospheric wet delays modeling over wide areas are investigated. A new, improved model is developed, applicable in real-time applications in China. Based on the GPT2w model, a modified parameter of zenith wet delay exponential decay wrt. height is introduced in the modeling of the real-time tropospheric delay. The accuracy of this tropospheric model and GPT2w model in different seasons is evaluated with cross-validation, the root mean square of the zenith troposphere delay (ZTD) is 1.2 and 3.6 cm on average, respectively. On the other hand, this new model proves to be better than the tropospheric modeling based on water-vapor scale height; it can accurately express tropospheric delays up to 10 km altitude, which potentially has benefits in many real-time applications. With the high-accuracy ZTD model, the augmented PPP convergence performance for BeiDou navigation satellite system (BDS) and GPS is evaluated. It shows that the contribution of the high-quality ZTD model on PPP convergence performance has relation with the constellation geometry. As BDS constellation geometry is poorer than GPS, the improvement for BDS PPP is more significant than that for GPS PPP. Compared with standard real-time PPP, the convergence time is reduced by 2–7 and 20–50% for the augmented BDS PPP, while GPS PPP only improves about 6 and 18% (on average), in horizontal and vertical directions, respectively. When GPS and BDS are combined, the geometry is greatly improved, which is good enough to get a reliable PPP solution, the augmentation PPP improves insignificantly comparing with standard PPP.     

PPP/PPP-RTK新进展与北斗/GNSS PPP定位性能比较

首先简要回顾了精密单点定位（PPP）技术在最近几年的发展现状,重点总结了高采样率钟差实时快速估计、多系统组合PPP模糊度固定、多频GNSS PPP模型及其模糊度固定、PPP快速初始化、PPP-RTK等若干热点方向的最新研究进展。在此基础上,利用目前四大卫星导航系统（GPS、GLONASS、Galileo、北斗）最新的实际观测数据,全面比较分析了各系统及多系统组合PPP定位性能,重点给出了北斗二号+北斗三号PPP浮点解和固定解的定位精度、收敛时间和首次固定时间。结果表明：我国北斗导航卫星系统已经可以实现与其他导航卫星系统基本相当的PPP定位性能。北斗二号+北斗三号组合PPP的收敛时间/首次固定时间20~30 min;静态解的东、北、天方向定位精度在毫米到厘米级;动态解水平方向约5 cm,高程方向约7 cm;多系统组合可显著提高PPP定位精度、收敛时间和首次固定时间：固定解定位精度比浮点解在东、北、天方向分别提升了14.8%、12.0%和12.8%;相比单GPS,多系统组合PPP浮点解的收敛时间和固定解首次固定时间分别缩短了36.5%和40.4%。     

GPS inter-frequency clock bias modeling and prediction for real-time precise point positioning

To ensure the consistent use of the current GPS precise satellite clock products, the inter-frequency clock bias (IFCB) should be carefully considered for triple-frequency precise point positioning (PPP). It is beneficial to investigate the modeling of the IFCB for multi-frequency PPP, especially for real-time users suffering from difficulties in real-time IFCB estimations. Our analysis is based on datasets from 129 stations spanning a whole year. A harmonic analysis is performed for all single-day IFCB time series, and periodic IFCB variations with periods of 12, 8, 6, 4.8, 4 and 3 h are identified. An empirical model composed of a sixth-order harmonic function and a linear function is presented to describe daily variations in the IFCB, and the modeling accuracy is 4 mm. A least squares fit is adopted to estimate the single-day harmonic coefficients phase and amplitude. The prediction accuracy of the IFCB models degrades from 7.2 to 12.3 mm when the time span of prediction is increased from a day to a week. When using IFCB models of the previous day to obtain the IFCB correction values, the positioning accuracy of triple-frequency PPP is improved by 21, 11 and 16% over the triple-frequency PPP neglecting the IFCB in the post-processing mode in the east, north and up directions, respectively. As to the real-time triple-frequency PPP, the corresponding accuracy improvement is 24, 9 and 10% in the three directions, respectively.     

GPT／2模型用于 GPS 大气可降水汽反演的精度分析

气象参数(温度T、气压P)是GPS大气可降水汽(PWV)反演中必不可少的数据,也是PWV反演的重要误差源之一。文中主要对GPT/2(GPT、GPT2)模型用于PWV反演的精度进行验证和分析。基于非差精密单点定位(PPP)技术,选取SuomiNet网9个测站的观测数据,借助研制的PPP软件,分别采用GPT模型、改进的GPT2模型以及测站实测气象数据进行大气可降水汽(PWV)反演。以实测气象数据处理结果为参考,对两种模型解算的PWV进行了对比和精度分析。结果表明:改进的GPT2模型优于GPT模型,尤其是当测站的高程较大时,GPT2模型的稳定性更优、适用性更广;采用GPT2模型解算的PWV偏差均值小于±1.0mm,精度(RMS)优于±1.5mm。在缺少实测气象数据的情况下,利用GPT2模型数据仍然能够取得较为理想的PWV反演结果。     

BDS/GPS组合精密单点定位精度分析与评价

精密单点定位（precise point positioning,PPP）已经广泛应用于许多领域,如测绘、交通、导航、地震监测等。近些年来,随着卫星数量的增多,多系统组合呈现越来越明显的趋势。利用全球MGEX（Multi-GNSS Experiment）网数据研究了BDS（BeiDou navigation satellite system）/GPS（global positioning system）组合精密单点定位技术,并与BDS单系统和GPS单系统进行了对比。结果表明,在静态定位中,BDS PPP在E、N、U方向的均方根误差分别为4.35 cm、3.01 cm、6.40 cm;GPS PPP在E、N、U方向的均方根误差分别为1.21 cm、0.48 cm、1.79 cm;BDS/GPS组合PPP在E、N、U方向的均方根误差分别为1.21 cm、0.50 cm、1.87 cm。在动态定位中,BDS PPP外符合精度水平方向优于10 cm,高程方向优于15 cm;GPS PPP和BDS/GPS组合PPP的外符合精度水平方向均优于5 cm,高程方向均优于8 cm。另外,无论是在静态还是动态的PPP中,组合系统相对于单系统,能大大缩短收敛时间,减少定位结果抖动,尤其是相对于BDS PPP来说,优势更为明显。