Various scientific applications and services increasingly demand real-time information on the effects of space weather on Earth's atmosphere. In this frame, the Royal Observatory of Belgium (ROB) takes advantage of the dense EUREF Permanent GNSS Network (EPN) to monitor the ionosphere over Europe from the measured delays in the GNSS signals, and provides publicly several derived products. The main ROB products consist of ionospheric vertical Total Electron Content (TEC) maps over Europe and their variability estimated in near real-time every 15 min on 0.5°· 0.5°grids using GPS observations. The maps are available online with a latency of~3 min in IONEX format at ftp://gnss.oma.be and as interactive web pages at www.gnss.be. This paper presents the method used in the ROB-IONO software to generate the maps. The ROB-TEC maps show a good agreement with widely used post-processed products such as IGS and ESA with mean differences of 1.3 ± 0.9 and 0.4 ± 1.6 TECu respectively for the period 2012 to mid-2013. In addition, we tested the reliability of the ROB-IONO software to detect abnormal ionospheric activity during the Halloween 2003 ionospheric storm. For this period, the mean differences with IGS and ESA maps are 0.9 ± 2.2 and 0.6 ± 6.8 TECu respectively with maximum differences (>38 TECu) occurring during the major phase of the storm. These differences are due to the lower resolution in time and space of both IGS and ESA maps compared to the ROB-TEC maps. A description of two recent events, one on March 17, 2013 and one on February 27, 2014 also highlights the capability of the method adopted in the ROB-IONO software to detect in near real-time abnormal ionospheric behaviour over Europe. In that frame, ROB maintains a data base publicly available with identified ionospheric events since 2012.
The R2CGGTTS software tool developed at the Royal Observatory of Belgium (ROB) to provide clock solutions in the standard Common GNSS Generic Time Transfer Standard (CGGTTS) has been extended to BeiDou Navigation Satellite System (BDS). The BDS includes satellites in three different orbits: 1) Medium Earth Orbit (MEO); 2) Inclined Geosynchronous Satellite Orbit (IGSO); and 3) Geostationary Earth Orbit (GEO). This paper presents first results obtained with this upgraded software, and a comparison between common view (CV) time transfer solutions obtained with either BDS, or GPS or Galileo. These preliminary results indicate that the BeiDou MEO satellites give time transfer results with a higher noise than the GPS results. This additional noise is shown to be due to some elevation-dependent delay in the BDS code measurements. Some biases were furthermore pointed out between the CV results obtained with the different BeiDou MEO satellites when the receivers used in the two stations are of different make. These biases may reach some nanoseconds, and find most probably their origin in the receiver hardware or firmware. It is shown additionally that using the BeiDou IGSO satellites and the GEO satellites, although increasing the number of observations, especially in the Asia-Pacific region, introduces a significant time transfer noise in the CV results.
When calibrating Global Positioning System (GPS) stations dedicated to timing, the hardware delays of P1 and P2, the P(Y)-codes on frequencies L1 and L2, are determined separately. In the international atomic time (TAI) network the GPS stations of the time laboratories are calibrated relatively against reference stations. This paper aims at determining the consistency between the P1 and P2 hardware delays (called dP1 and dP2) of these reference stations, and to look at the stability of the inter-signal hardware delays dP1-dP2 of all the stations in the network. The method consists of determining the dP1-dP2 directly from the GPS pseudorange measurements corrected for the frequency-dependent antenna phase center and the frequencydependent ionosphere corrections, and then to compare these computed dP1-dP2 to the calibrated values.Our results show that the differences between the computed and calibrated dP1-dP2 are well inside the expected combined uncertainty of the two quantities. Furthermore, the consistency between the calibrated time transfer solution obtained from either singlefrequency P1 or dual-frequency P3 for reference laboratories is shown to be about 1.0 ns, well inside the 2.1 ns uB uncertainty of a time transfer link based on GPS P3 or Precise Point Positioning. This demonstrates the good consistency between the P1 and P2 hardware delays of the reference stations used for calibration in the TAI network.The long-term stability of the inter-signal hardware delays is also analysed from the computed dP1-dP2. It is shown that only variations larger than 2 ns can be detected for a particular station, while variations of 200 ps can be detected when differentiating the results between two stations. Finally, we also show that in the differential calibration process as used in the TAI network, using the same antenna phase center or using different positions for L1 and L2 signals gives maximum differences of 200 ps on the hardware delays of the separate codes P1 and P2; however, the final impact on the P3 combination is less than 10 ps.
Global navigation satellite system (GNSS), notably global positioning system (GPS), has been utilized for more than a decade in the deformation monitoring of a variety of stationary structures such as dams, building, slopes, etc., around the world. With the technological advent of GPS positioning, telecommunications, and signal processing, as well as public awareness, GPS has been widely used in recent years for monitoring slender structures such as large suspension bridges and high‐rise buildings. This article briefly reviews the history of GNSS for SHM of different civil structures, with its focus on the applications of GNSS positioning for long suspension bridge deformation monitoring. It is followed by a discussion on the architecture of GNSS centered SHM system, which consists of subsystems such as instrumentation, data acquisition and transmission, data processing, visualization of deformations, and interface with dedicated analytical models. The issues in using GNSS for SHM are addressed by the authors and also relevant solutions are introduced in the article. At the end of the article, the authors present their future vision about GNSS for SHM.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.