基于实时精密单点定位技术的暴雨短临预报

提出了一种将实时精密单点定位(Precise Point Positioning, PPP)技术用于暴雨短临预报的新方法.该方法首先基于GPS连续运行参考站网(Continuously Operating Reference Stations, CORS)实时估计的精密卫星钟差完成PPP解算,再以实时获取的对流层延迟(Zenith Tropospheric Delay, ZTD)及其增量变化为依据进行暴雨短临预报.研究结果表明:一般雷暴天气来临之前的2~6 h,ZTD增量表现为先后突破±5 mm/5 min,且后续记录到的实际降水量大小与ZTD维持在高水平阶段的时间长短有较好的对应关系;就热带气旋而言,在强风作用下,ZTD增量变化表现的异常活跃和复杂,规律性较弱,但对短临预报强降雨仍有一定的指示作用.     

Deformation caused by the 2011 eastern Japan great earthquake monitored using the GPS single-epoch precise point positioning technique

Crustal deformation can provide constraints for studying earthquake rupture and shock wave transmission for the Mw9.0 eastern Japan great earthquake. Using the single-epoch precise point positioning (PPP) method and the appropriate positioning flow, we process GPS data from six IGS (International GNSS Service) sites (e.g., MIZU, TSK2, USUD, MTKA, AIRA and KSMV) located in Japan and obtain the positioning results with centimeter scale precision. The displacement time series of the six sites are analyzed using the least squares spectral analysis method to estimate deformations caused by the Mw9.0 mainshock and the Mw7.9 aftershock, and the cumulative displacements after 1 day. Mainshock displacements at station MIZU, the nearest site to the mainshock in the North (N), East (E), and Up (U) directions, are ?1.202 m, 2.180 m and ?0.104 m, respectively, and the cumulative deformations after 1 day are ?1.117 m, 2.071 m and ?0.072 m, respectively. The displacements at station KSMV, the nearest site to the Mw7.9 aftershock in the N, E and U directions, are ?0.032 m, 0.742 m and ?0.345 m, respectively. The other sites obviously experienced eastern movements and subsidence. The deformation vectors indicate that the horizontal displacements caused by the earthquake point to the epicenter and rupture. Elastic bounds evidently took place at all sites. The results indicate that the crustal movements and earthquake were part of a megathrust caused by the Pacific Plate sinking under the North American Plate to the northeast of Japan island arc.     

LEO GPS接收机仪器偏差估计

LEO GPS观测已成为空间电离层研究重要手段之一,通过GPS双频观测值获取的TEC则是电离层探测的一个重要参量,为获取高精度TEC需估计和消除GPS接收机仪器偏差（DCB）.本文旨在探索一种全新的LEO GPS接收机仪器偏差的估计方法：基于电离层球对称的假设,利用CHAMP和COSMIC原始GPS观测数据,采用几何映射函数,通过最小二乘解算出GPS接收机仪器偏差.结果表明：(1)2008年1月份期间,通过上述方法解算的仪器偏差都较稳定,相比COSMIC网上发布结果,标准偏差都在0.6 ns以内;（2）COSMIC（轨道高度大约800 km）仪器偏差估计结果优于CHAMP（轨道高度大约400 km）的结果,原因为：对于不同轨道高度LEO GPS仪器偏差估计,其较高轨道高度的电离层球对称假设影响较小.     

中国区域GPS单频点定位在不同类型磁暴主相期间定位性能分析

地磁暴期间,电离层可出现不同程度的扰动,显著影响GNSS导航系统性能.本文针对GNSS系统应用需求,全面分析了不同等级磁暴主相期间GPS单频点定位精度在中国区域(地磁中、低纬地区)的受扰情况.结果表明,定位误差极端值的出现概率与磁暴等级呈正相关,也与测站纬度相关(低纬一般高于高纬),定位精度在U(垂直)方向受影响程度明...     

对GPS接收机测试评估的探讨

随着GPS的广泛应用和GPS产业的迅速发展，GPS厂家众多，生产的接收机类型更是数以百计，整个GPS接收机市场可以说是鱼目混珠，识别困难；大多数购买者只能听信厂家的技术指标，如何对GPS接收机的性能进行测试评估的意义显得很重要，本文基于此对GPS接收机测试评估展开探讨和研究。     

精密单点定位整周模糊度快速固定

提出利用GPS参考网估计电离层延迟、卫星相位偏差的算法,用于实现区域内精密单点定位(Precise Point Positioning, PPP)的整周模糊度快速固定.利用站间距约为100~200 km的参考网进行实验,结果表明:电离层延迟的内插和外推精度均优于1 dm,卫星相位偏差估值的日内变化不超过0.2周;此外,单天内不同时刻始,固定PPP整周模糊度所需时长最多不超过10 min,且当模糊度成功固定后,三维位置解较之相应浮点解的精度改善优于80%.新算法可望解决PPP普遍存在的收敛时间过长问题,增强了PPP技术的实用性.     

精密单点定位整周模糊度快速固定

提出利用GPS参考网估计电离层延迟、卫星相位偏差的算法,用于实现区域内精密单点定位(Precise Point Positioning, PPP)的整周模糊度快速固定.利用站间距约为100~200 km的参考网进行实验,结果表明:电离层延迟的内插和外推精度均优于1 dm,卫星相位偏差估值的日内变化不超过0.2周;此外,单天内不同时刻始,固定PPP整周模糊度所需时长最多不超过10 min,且当模糊度成功固定后,三维位置解较之相应浮点解的精度改善优于80%.新算法可望解决PPP普遍存在的收敛时间过长问题,增强了PPP技术的实用性.     

COSMIC低轨卫星GPS接收机差分码偏差估计

GPS接收机差分码偏差（Differential Code Bias,DCB）是利用COSMIC低轨卫星观测值反演电离层总电子含量TEC的一项重要误差源.本文将COSMIC卫星轨道高度以上的电离层作为一个单层,采用球谐函数来参数化电离层TEC值,并利用最小二乘法同时估算电离层球谐系数和DCB参数.运用这种方法对2012年12月份的所有COSMIC卫星GPS接收机DCB进行了解算,并与COSMIC数据分析与档案中心CDAAC提供的产品进行了比较.实验结果表明：在2012年12月期间,估计的接收机DCB与CDAAC结果符合的较好,二者DCB变化趋势相近,DCB差值的RMS值在2 TECU以内,且最大绝对差值小于3 TECU;此外,本文计算的接收机DCB估计误差主要分布在0.2~0.4 TECU之间,具有较高的内符合精度.     

利用精密单点定位求解电离层延迟

近年来,高时空分辨率的全球导航卫星系统(GNSS)观测信号已成为电离层研究的重要资源.利用GNSS研究电离层,需首先将观测资料转换成包含电离层信息的可观测量(Ionospheric Observables,称之为"电离层观测值").目前,最常用的电离层观测值一般采用联合无几何影响组合的码和相位观测,利用相位平滑伪距方法计算得到(称之为"平滑电离层观测值"),但该过程易受平滑弧段长度和与测站有关的误差(如多路径效应和观测噪声)的影响.本文提出利用精密单点定位(Precise Point Positioning, PPP)提取电离层观测值(称之为"PPP电离层观测值",形式与平滑电离层观测值相同).与相位平滑伪距相比,IGS发布的卫星轨道、钟差产品可被PPP合理利用,从而有效减少了待估参数,使得电离层观测值的估计精度得到改善.基于短基线和零基线实验,通过考察两类电离层观测值的站间单差结果在各卫星弧段间的离散程度,验证了PPP电离层观测值的可靠性:以某两天的短基线实验结果为例,与测站有关的误差对PPP电离层观测值的影响分别为对平滑电离层观测值影响的44.4%和35.7%,表明PPP电离层观测值更利于高精度电离层建模、预报等研究.     

基于服务系统的实时精密单点定位技术及应用研究

讨论了实时精密单点定位的若干关键技术,着重研究了实时精密钟差估计算法;利用全球40个IGS跟踪站连续、实时的观测数据流进行实时精密卫星钟差估计,解算出的实时精密钟差与CODE事后精密钟差具有较好的一致性,二者互差的RMS优于0.2 ns.采用实时估计的卫星钟差和IGS发布的超快速精密卫星轨道进行实时精密单点定位模拟实验,结果表明：经过大约15~30 min初始化后,实时精密单点定位滤波收敛之后水平方向的定位精度优于5 cm,高程方向的精度优于10 cm,能满足在该精度级别的实时用户的定位需求.处理汶川地震期间震区的GPS观测数据,结果表明实时精密单点定位能够探测地震发生期间的地面同震位移.     

Quality assessment of onboard GPS receiver and its combination with DORIS and SLR for Haiyang 2A precise orbit determination

The GPS,DORIS,and SLR instruments are installed on Haiyang 2A(HY2A)altimetry satellite for Precise Orbit Determination(POD).Among these instruments,the codeless GPS receiver is the state-of-art Chinese indigenous onboard receiver,and it is the first one successfully used for Low Earth Orbit(LEO)satellite.Firstly,the contribution assesses the performance of the receiver through an analysis of data integrity,numbers of all tracked and valid measurements as well as multipath errors.The receiver generally shows good performance and quality despite a few flaws.For example,L2 observations are often missing in low elevations,particularly during the ascent of GPS satellites,and the multipath errors of P1 show a slightly abnormal pattern.Secondly,the PCO(Phase Center Offset)and PCV(Phase Center Variation)of the antenna of the GPS receiver are determined in this contribution.A significant leap for Z-component of PCO up to-1.2 cm has been found on 10 October 2011.Thirdly,the obtained PCO and PCV maps are used for GPS only POD solutions.The post-fit residuals of ionosphere-free phase combinations reduce almost 50%,and the radial orbit differences with respect to CNES(Centre National d’Etudes Spatiales)Precise Orbit Ephemeris(POEs)improve about 13.9%.The orbits are validated using the SLR data,and the RMS of SLR Observed minus Computed(O-C)residuals reduces from 17.5 to 15.9 mm.These improvements are with respect to the orbits determined without PCO and PCV.Fourthly,six types of solutions are determined for HY2A satellite using different combinations of GPS,DORIS,and SLR data.Statistics of SLR O-C residuals and cross-comparison of orbits obtained in the contribution and the CNES POEs indicate that the radial accuracy of these orbits is at the 1.0 cm level for HY2A orbit solutions,which is much better than the scientific requirements of this mission.It is noticed that the GPS observations dominate the achievable accuracy of POD,and the combination of multiple types of observations can reduce orbit errors caused by data gaps and maintain more stable and continuous orbits.     

Strong motion displacement waveforms using 10‐Hz precise point positioning GPS: an assessment based on free oscillation experiments

The recently developed precise point positioning (PPP) technique permits to compute instantaneous coordinates of a GPS station relatively to distant reference stations and waveforms of ground displacements during strong motions at the 1 Hz level. This is another application of GPS, different from the computation of static coseismic movements or of accurate monitoring of dynamic displacements of structures using a static receiver and a nearby moving receiver (DGPS). Recently, earthquake ground displacement waveforms using 10‐Hz GPS data have also been calculated, but no independent evidence to assess their quality exists. To overcome this problem, we evaluated the output of 10‐Hz PPP results on the basis of supervised learning experiments. Semistatic and dynamic displacements (damped harmonic oscillations) of known characteristics of the order of a few centimeter were produced and were recorded by GPS, an accelerometer, and a robotic total station. Time series of instantaneous displacements were analyzed using different PPP techniques and were compared with reference (true) values derived from DGPS and the other sensors. Our analysis revealed that the PPP‐derived coordinates are contaminated by long‐period noise but they can display the details of semistatic displacements, while their short‐period component describes well the pattern of waveforms and spectra (at least up to 4 Hz) of dynamic displacements, with up to 20 mm accuracy for isolated points. These results indicate that 10‐Hz PPP‐GPS is useful for earthquake engineering and can safely be used to reconstruct waveforms of deflections of the ground and of various points on structures during strong motions. Copyright © 2014 John Wiley & Sons, Ltd.     

Improving GPS positioning estimates during extreme weather situations by the help of fine-mesh numerical weather models

Space geodetic applications require to model troposphere delays as good as possible in order to achieve highly accurate positioning estimates. However, these models are not capable to consider complex refractivity fields which are likely to occur during extreme weather situations like typhoons, storms, heavy rain-fall, etc. Thus it has been investigated how positioning results can be improved if information from numerical weather models is taken into account. It will be demonstrated that positioning errors can be significantly reduced by the usage of ray-traced slant delays. Therefore, meso-scale and fine-mesh numerical weather models are utilized and their impact on the positioning results will be measured. The approach has been evaluated during a typhoon passage using global positioning service (GPS) observations of 72 receivers located around Tokyo, proving the usefulness of ray-traced slant delays for positioning applications. Thereby, it is possible reduce virtual station movements as well as improve station height repeatabilities by up to 30% w.r.t. standard processing techniques. Additionally the advantages and caveats of numerical weather models will be discussed and it will be shown how fine-mesh numerical weather models, which are restricted in their spatial extent, have to be handled in order to provide useful corrections.     

A new approach of single epoch GPS posi- tioning for landslide monitoring

Introduction China is a country with many landslides and debris flows. These disasters bring out a large amount of losses of life and property. It is significant to predict landslide incident by monitoring the deformations of these landslides. At past, triangulation and trilateration are traditional tools, but it is very difficult for them to realize real-time monitoring, and it is more dangerous for obser- vation workers when the deformation becomes larger. Because of many advantages such as…     

单站GPS测速在实时地震监测中的应用

本文提出一种利用单站GPS载波相位或多普勒观测数据,基于单站GPS测速法实时确定地震监测台站运动状态(速度)的新方法.针对2010年4月4日发生于墨西哥Baja California(32.259°N,115.287°W)北部的Mw7.2级EI-Mayor-Cucapah地震事件,选取震中邻近区域(200 km内)若干采样率为5 Hz的高频GPS观测站数据进行实验.结果表明:基于新方法所得测站速度结果能够很好地反映出地震期间监测台站的瞬时运动状态,测站P496和P744计算的速度结果与其并置强震仪观测结果具有很好的一致性.     

基于CORS网络的单频GPS实时精密单点定位新方法

利用单频接收机实现大范围、高精度快速实时定位是卫星大地测量研究的热点和难点问题之一.本文提出了一套基于连续运行参考站系统(CORS)的误差实时建模数据处理方法,设计并实现了一种新的GPS单频接收机实时精密单点定位服务方法.然后,利用山西省CORS网内一组实测动态数据,以及从湖北省CORS网和武汉市CORS网选取的一组实测静态数据进行测试,验证分析了所提出方法用于实时定位服务的可行性.结果表明:对于站间平均距离小于71 km的参考网,网内单频用户按照实时处理模式,在经过数秒钟的初始化后即可获得厘米级的动态精密单点定位结果.这为GPS单频接收机用户实现快速实时精密单点定位提供了一种可行的新方法.     

Swarm卫星星载接收机GPS信号中断统计特征分析

本文聚焦于欧空局Swarm卫星星载接收机在中纬地区出现的GPS信号中断事件, 利用其近9年(2014年1月至2022年9月)的观测数据, 详细统计了GPS信号中断事件发生的时空分布特征及与背景等离子体密度起伏的关系.研究结果表明Swarm卫星在其接收机锁相环带宽从0.75 Hz调整至1.0 Hz前后, GPS信号中断事件表现出不同的时空分布特征.在前一个时期, 2014年1月1日至2016年8月11日, GPS信号中断事件主要分布在低纬磁赤道附近和高纬极区附近, 少量中断事件分布在中国东部地区; 而在后一个时期, 2016年8月12日至2022年9月30日, GPS信号中断事件则出现在了所有的纬度, 同时表现出显著的经度差异.前一个时期内GPS信号中断事件表现出了明显的季节依赖, 而后一个时期内出现的GPS信号中断事件则出现了无季节特性的弥散状分布.该结果表明当Swarm星载接收机锁相环带宽调整至1.0 Hz时, 虽然提升了其应对电离层闪烁条件下多普勒频移的动态调整范围, 但同时也增加了接收机载波相位观测的热噪声, 进而导致接收机产生了一些随机的短时信号中断.除了上述不同, 两个时期内的GPS信号中断事件也表现出了一些共同特征, 比如信号中断事件主要均集中在GPS卫星相对于Swarm处于较低仰角(＜20°)的情况下; 同时这些事件主要发生在发射较早的Block ⅡR和Block ⅡA类型GPS卫星上, 暗示了随着发射年限的增加与星载设备的老化, GPS卫星的稳定性会逐渐降低.通过进一步对比分析Swarm卫星出现与未出现GPS信号中断轨道对应的原位电子密度观测数据, 发现GPS信号中断的轨道其对应的电子密度波动更剧烈, 表明背景等离子体密度的梯度强度是引起Swarm星载接收机在中纬地区出现GPS信号中断的重要原因.本文的研究结果对于星载接收机的设计优化, 特别是提升其在电离层闪烁条件下的稳定性有重要的参考意义.

     

基于GNSS网络的实时精密单点定位及精度分析

基于局域GNSS网络,以历元间、星间差分技术实时估计了GPS卫星相对钟差的历元间差值;针对所估计实时精密钟差的特征,推导了实时精密单点定位的估计模型.对所估计得到的相对钟差的历元间差值、实时定位结果分别进行了比较、分析.结果表明,相对钟差的历元间差值与IGS的最终星历相比其精度可以达到0.08 ns;每小时观测的实时静态定位结果在N、E、U三个方向的精度分别为1.47、3.62、4.09 cm.动态模式,实时结果在N、E、U三个方向的精度分别为2.63、3.82、5.20 cm.与采用IGS最终轨道和钟差解算的结果相比较,实时计算结果优于采用精密轨道和精密钟差计算结果.     

The impact of temporal ionospheric gradients in Northern Europe on relative GPS positioning

The effect of temporal ionospheric gradients on measured baselines was studied at mid and high latitudes. The experimental analysis was carried out from 14 to 17 July 2000 (day of year (DOY) from 196 to 199), which includes both quiet and stormy days for comparison purposes. Temporal ionospheric gradients caused by the geomagnetic storm affect the ambiguity resolution, resulting in unresolved ambiguities up to 61% for the time periods 21:00–24:00 UT on DOY 197 and 00:00–03:00 UT on DOY 198 for the Kiru-Soda and Kiru-Tro1 baselines (high-latitude, K_p>7). RMS of epoch by epoch coordinate residual change gradually increases from 1.45, 0.96 and 3.67 cm at 9:00–12:00 UT on DOY 197 to 1.79, 1.22 and 4.61 cm at 0:00–03:00 UT on DOY 198 (K_p>8) for the same baselines’ north, east and up coordinate components, respectively. There are no remarkable effects for the selected baselines in the mid-latitude region in both ambiguities and coordinate components.     

The response of TEC at quasi-conjugate point GPS stations during solar flares

Global Positioning System (GPS) derived total electron content (TEC) measurements were analyzed to investigate the ionospheric response during the X-class solar flare event that occurred on 5-6 December 2006 at geomagnetic conjugate stations: Syowa, Antarctica (SYOG) (GC: 69.00°S, 39.58°E; CGM: 66.08°S, 71.65°E) and árholt, Iceland (ARHO) (GC: 66.19°N, 342.89°E; CGM: 66.37°N, 71.48°E). Bernese GPS software was used to derive the TEC maps for both stations. The focus of this study is to determine the symmetry or asymmetry of TEC values which is an important parameter in the ionosphere at conjugate stations during these solar flare events. The results showed that during the first flares on 5 December, effects were more pronounced at SYOG than at ARHO. However, on 6 December, the TEC at ARHO showed a sudden spike during the flare with a different TEC variation at SYOG.