Trans-ionospheric GPS signal delay gradients observed over mid-latitude Europe during the geomagnetic storms of October–November 2003

Ionospheric disturbances are known to have adverse effects on the satellite-based communication and navigation. One particular type of ionospheric effects, observed during major geomagnetic storms and threatening the integrity performance of both ground-based and space-based GNSS augmentation systems, is the sharp increase/decrease in the ionospheric delay that propagates in horizontal direction, thus called for convenience ‘moving ionospheric wall’. This paper presents preliminary results from researching such anomalous ionospheric delay gradients at European middle latitudes during the storm events of 29 October 2003 and 20 November 2003. For the purpose, 30-s GPS data from the Belgian permanent network was used for calculating and analysing the slant ionospheric delay and total electron content values. It has been found that, during these two particular storm events, substantial gradients did occur in Europe although they were not so pronounced as in the American sector.     

WAAS系统中电离层折射校正的新方法及计算结果

电离层介质的色散性是影响电磁波信号进行卫星导航定位精度的重要因素之一.配合北斗二代分系绩研制任务,提出了一种新的电离层折射校正算法,并利用2000年7月1日到3日的双频GPS观测数据对6个用户站进行试算,进一步将试算所得均方根误差和电离层网格算法得到的误差进行比较.结果表明,对于中纬区域的用户站,估算的TEC误差约为0.5 m左右;而低纬用户误差相对增大,为1 m左右.文中给出的算法与电离层网格模型所提供的精度相差不多,在未来中国自主的卫星增强系统中采用新方法进行电离层进行修正是可行的及有效的.      

Monitoring of long-term land subsidence from 2003 to 2017 in coastal area of Semarang,Indonesia by SBAS DInSAR analyses using Envisat-ASAR,ALOS-PALSAR,and Sentinel-1A SAR data

Land subsidence is a critical issue that large cities located in coastal areas, such as Semarang, Indonesia, must address. The monitoring of land subsidence is vital for predicting and mitigating the disasters that such subsidence may cause. Therefore, an economical and effective monitoring method, which can continuously provide accurate measurements over extensive areas, is highly required. Differential Interferometry Synthetic Aperture Radar (DInSAR) has the potential to be a powerful technique that can meet the above demands. Actually, DInSAR has been applied to monitor the subsidence in Semarang, but it was for a limited period before 2012.In order to clarify the transition of the long-term subsidence behavior in Semarang, the Small Baseline Subset (SBAS) method, which is one type of time-series DInSAR, is employed in this research. The sets of data of Envisat-ASAR (2003–2007), ALOS-PALSAR (2007–2011), and Sentinel-1A (2015–2017) are employed for the analyses. Then, the validity of the SBAS results is discussed from the viewpoints of both spatial distribution and temporal transition using GPS displacement measurement results and the geological conditions of the ground.On the other hand, as the lifespan of SAR satellites is commonly designed to be around 5–7?years, an appropriate method, which can connect the subsidence provided independently by the unlinked time-series data sets of the three different SAR satellite data, is required. This study uses the Hyperbolic Method (HM) to connect the above unlinked SBAS results. The HM is often used to fit the monitored subsidence in practice as a geotechnical engineering tool. Using this method, 14?years of the temporal behavior of the subsidence in Semarang is evaluated.It is found that the transition of the subsidence is different depending on the location, and that the subsidence rate is still increasing in the north and northeast parts of the coastal area. This study shows that SBAS DInSAR can be a useful tool for long-term continuous subsidence monitoring.     

Design of BDS-3 integrity monitoring and preliminary analysis of its performance

With the improvement in the service accuracy and expansion of the application scope of satellite navigation systems, users now have high demands for system integrity that are directly related to navigation safety. As a crucial index to measure the reliability of satellite navigation systems, integrity is the ability of the system to send an alarm when an abnormity occurs. The new-generation Beidou Navigation Satellite System (BDS-3) prioritized the upgrading of system integrity as an important objective in system construction. Because the system provides both basic navigation and satellite-based augmentation system (SBAS) services by the operational control system, BDS-3 adopts an integrated integrity monitoring and processing strategy that applies satellite autonomous integrity monitoring and ground-based integrity monitoring for both the basic navigation service and SBAS navigation service. BDS-3 also uses an improved and refined integrity parameter system to provide slow, fast and real-time integrity parameters for basic navigation, and provide SBAS-provided integrity information messages in accordance with Radio Technical Commission for Aeronautics (RTCA) specification and dual frequency, multi-constellation (DFMC) specification to support the SBAS signal frequency, single constellation operation and DFMC operation respectively. The performance of BDS-3 system integrity monitoring is preliminarily verified during on-orbit testing in different states, including normal operation, satellite clock failure and satellite ephemeris failure. The results show that satellite autonomous integrity monitoring, ground-based integrity monitoring and satellite-based augmentation all correctly work within the system. Satellite autonomous integrity monitoring can detect satellite clock failure but not satellite orbit failure. However, ground-based integrity monitoring can detect both. Moreover, the satellite-based augmentation integrity system monitors the differential range error after satellite ephemeris and clock error corrections based on user requirements. Compared to the near minute-level time-to-alert capability of ground-based integrity monitoring, satellite autonomous integrity monitoring reduces the system alert time to less than 4 s. With a combined satellite-ground monitoring strategy and the implementation of different monitoring technologies, the BDS-3 integrity of service has been considerably improved.     

Beidou wide-area augmentation system clock error correction and performance verification

On December 27, 2018, the Beidou-3 System (BDS-3) has completed the deployment of 18 Medium Earth Orbit (MEO) satellites combined as a space constellation. In addition to the augmentation information for the new system signals B1C and B2a, the BDS-3 is compatible with the three augmentation information broadcast by the BDS-2 system for B1I and B3I signals: equivalent clock error correction, User Differential Ranging Error (UDRE) and Grid Ionosphere Vertical Error (GIVE). In this paper, the observation data of Beidou monitoring network are used to analyze the pseudo-range observation quality of the smooth transition signals B1I and B3I of BDS-2 and BDS-3. At the same time, the relationship between the equivalent clock error correction and the prediction error of the satellite clock is analyzed by using the Two-Way Satellite Time and Frequency Transfer (TWSTFT) data. The results show that the correlation between the equivalent clock error correction and the monitored clock error by using the TWSTFT data is greater than 60%. We calculate the UDRE by using the equivalent clock error correction. The results show that the satellite equivalent clock error correction can improve the accuracy of User Equivalent Range Error (UERE) by about 50%. This paper also compares the positioning accuracy of the BDS-2 satellites with the BDS-2 satellites combined BDS-3 satellites. The results show that the three-dimensional positioning accuracy is improved by about 30% after the BDS-3 satellites are added.     

空间信号完好性监测技术研究

星基增强导航系统(SBAS)通过向用户提供用户差分距离误差(UDRE:User Differential RangeError),来保证广播星历和星钟改正数的精度。本文设计了UDRE的一种改进算法,建立卫星导航系统星钟和星历误差的状态方程和量测方程,进行卡尔曼滤波计算星历与星钟误差改正数与改正精度,通过滤波误差估计精度矩阵计算UDRE,并做了相应的仿真分析和比较,结果表明:改进算法能够对UDRE做出更好的估计来满足星历及钟差改正误差相对应的伪距误差的置信限值。     

NeQuick G model based scale factor determination for using SBAS ionosphere corrections at low earth orbit

A space-based augmentation system (SBAS) provides real-time correction data for global navigation satellite system (GNSS) users near ground. In order to use the SBAS ionosphere correction for low Earth orbit (LEO) satellites, the correction should be scaled down for the LEO altitude. This scale factor varies with ionosphere distribution and it is hard to determine the value at LEO in real time. We propose a real-time scale factor determination method by using Galileo GNSS’s NeQuick G model. A LEO satellite GPS data and SBAS data received on ground were used to evaluate the performance of the NeQuick G derived variable scale factor. The NeQuick G derived scale factor shows a significant accuracy improvement over NeQuick G model or pre-determined constant scale factor. It improves a vertical positioning accuracy of the LEO satellite. The error mean reductions of the vertical positioning over NeQuick G and the constant scale factor are 31.5% and 11.7%, respectively.     

WAAS卫星播发电文一致性分析

星基增强系统(SBAS)是在传统GNSS的基础上为了进一步满足民航用户对卫星导航系统越来越高的精度、完好性、连续性和可用性需求而应运而生.目前全球已建立起了多个SBAS系统,其中提供服务时间最长的是美国的WAAS系统.WAAS系统包括38个参考站、3个主控站、6个上注站和3颗GEO卫星,每个参考站配备3套独立的监测接收...     

北斗星基增强电离层模型精度评估与分析

针对如何有效地对北斗星基增强系统(SBAS)电离层在模型精度、模型时效性等方面进行综合评估,提出了一种修正的CODE格网模型,通过增加国内陆态网监测站观测数据,提升了CODE格网模型精度。以此模型为基准,利用2020年近一个月的数据分析了北斗区域格网电离层模型和北斗SBAS电离层模型的延迟误差、改正比例的变化以及在全球的覆盖范围,并从全球不同纬度带比较了北斗基本导航和星基增强电离层模型的精度。结果表明：修正的CODE模型精度符合评估要求,且与我国电离层实际变化情况更吻合,北斗区域格网电离层模型和北斗SBAS电离层模型精度相当,优于0.3m,改正比例均优于80%,但北斗SBAS电离层模型覆盖范围明显更大。     

卫星导航进近技术进展

全球卫星定位系统（GNSS）增强系统能提供全天候无间断的卫星导航信号，可以辅助飞机进行进近。本文介绍了全球卫星导航系统进近着陆系统的基本组成、工作原理和功能特点，并对国内外研究进展进行了阐述。针对GNSS进近研究中的热点问题，重点论述了地基增强系统（GBAS）、星基增强系统（SBAS）、用户自主完好性监测（RAIM）等技术的发展现状，指出了GNSS进近技术实际工程应用仍然存在的问题，探讨了GNSS进近技术未来的发展方向。