Inter-technique validation of tropospheric slant total delays

Abstract. An extensive validation of line-of-sight tropospheric slant total delays (STD) from Global Navigation Satellite Systems (GNSS), ray tracing in numerical weather prediction model (NWM) fields and microwave water vapour radiometer (WVR) is presented. Ten GNSS reference stations, including collocated sites, and almost 2 months of data from 2013, including severe weather events were used for comparison. Seven institutions delivered their STDs based on GNSS observations processed using 5 software programs and 11 strategies enabling to compare rather different solutions and to assess the impact of several aspects of the processing strategy. STDs from NWM ray tracing came from three institutions using three different NWMs and ray-tracing software. Inter-techniques evaluations demonstrated a good mutual agreement of various GNSS STD solutions compared to NWM and WVR STDs. The mean bias among GNSS solutions not considering post-fit residuals in STDs was −0.6 mm for STDs scaled in the zenith direction and the mean standard deviation was 3.7 mm. Standard deviations of comparisons between GNSS and NWM ray-tracing solutions were typically 10 mm ± 2 mm (scaled in the zenith direction), depending on the NWM model and the GNSS station. Comparing GNSS versus WVR STDs reached standard deviations of 12 mm ± 2 mm also scaled in the zenith direction. Impacts of raw GNSS post-fit residuals and cleaned residuals on optimal reconstructing of GNSS STDs were evaluated at inter-technique comparison and for GNSS at collocated sites. The use of raw post-fit residuals is not generally recommended as they might contain strong systematic effects, as demonstrated in the case of station LDB0. Simplified STDs reconstructed only from estimated GNSS tropospheric parameters, i.e. without applying post-fit residuals, performed the best in all the comparisons; however, it obviously missed part of tropospheric signals due to non-linear temporal and spatial variations in the troposphere. Although the post-fit residuals cleaned of visible systematic errors generally showed a slightly worse performance, they contained significant tropospheric signal on top of the simplified model. They are thus recommended for the reconstruction of STDs, particularly during high variability in the troposphere. Cleaned residuals also showed a stable performance during ordinary days while containing promising information about the troposphere at low-elevation angles.

Download Full-text

Inter-technique validation of tropospheric slant total delays

10.5194/amt-2016-372 ◽

2017 ◽

Cited By ~ 1

Author(s):

Michal Kačmařík ◽

Jan Douša ◽

Galina Dick ◽

Florian Zus ◽

Hugues Brenot ◽

...

Keyword(s):

Ray Tracing ◽

Prediction Models ◽

Weather Prediction ◽

Global Navigation Satellite Systems ◽

Satellite Systems ◽

Weather Events ◽

All Solutions ◽

Systematic Effects ◽

Standard Deviations ◽

Global Navigation Satellite

Abstract. An extensive validation of line-of-sight tropospheric Slant Total Delays (STD) from Global Navigation Satellite Systems (GNSS), ray-tracing in Numerical Weather Prediction Models (NWM) fields and microwave Water Vapour Radiometer (WVR) is presented. Ten GNSS reference stations and almost two months of data from 2013, including severe weather events, entered the comparison. Seven institutions delivered their STDs based on GNSS observations processed using five software and eleven strategies. STDs from NWM ray-tracing came from three institutions using three different NWM models. Results show generally a very good mutual agreement among all solutions from all the techniques. The mean bias (over all stations) between the GNSS solution selected as reference, which did not use post-fit residuals in STDs, and all other GNSS solutions without post-fit residuals is −0.6 mm for STDs scaled in the zenith direction, and the corresponding mean standard deviation is 3.7 mm. Standard deviations of comparisons between GNSS a NWM ray-tracing solutions are typically 10 mm ± 2 mm (scaled in the zenith direction), depending on the NWM model and the particular station considered. When comparing GNSS versus WVR STDs, standard deviations reached 12 mm ± 2 mm, as scaled in zenith direction. Moreover, the influence of adding raw GNSS post-fit residuals, as well as residuals screened out of systematic effects, to STDs was studied. It was found that adding raw post-fit residuals always led to lower quality of GNSS STDs while the situation was not that straightforward after the post-fit residuals cleaning.

Download Full-text

On the Impact of Channel Cross-Correlations in High-Sensitivity Receivers for Galileo E1 OS and GPS L1C Signals

International Journal of Navigation and Observation ◽

10.1155/2012/132078 ◽

2012 ◽

Vol 2012 ◽

pp. 1-10 ◽

Cited By ~ 3

Author(s):

Davide Margaria ◽

Beatrice Motella ◽

Fabio Dovis

Keyword(s):

Cross Correlation ◽

High Sensitivity ◽

Global Navigation Satellite Systems ◽

Integration Time ◽

Noise Component ◽

Satellite Systems ◽

Coherent Integration ◽

Global Navigation Satellite ◽

Correlation Properties ◽

The Impact

One of the most promising features of the modernized global navigation satellite systems signals is the presence of pilot channels that, being data-transition free, allow for increasing the coherent integration time of the receivers. Generally speaking, the increased integration time allows to better average the thermal noise component, thus improving the postcorrelation SNR of the receiver in the acquisition phase. On the other hand, for a standalone receiver which is not aided or assisted, the acquisition architecture requires that only the pilot channel is processed, at least during the first steps of the procedure. The aim of this paper is to present a detailed investigation on the impact of the code cross-correlation properties in the reception of Galileo E1 Open Service and GPS L1C civil signals. Analytical and simulation results demonstrate that the S-curve of the code synchronization loop can be affected by a bias around the lock point. This effect depends on the code cross-correlation properties and on the receiver setup. Furthermore, in these cases, the sensitivity of the receiver to other error sources might increase, and the paper shows how in presence of an interfering signal the pseudorange bias can be magnified and lead to relevant performance degradation.

Download Full-text

CODE IGS reference products including Galileo

10.5194/egusphere-egu2020-18142 ◽

2020 ◽

Author(s):

Lars Prange ◽

Arturo Villiger ◽

Stefan Schaer ◽

Rolf Dach ◽

Dmitry Sidorov ◽

...

Keyword(s):

Rapid Analysis ◽

Global Navigation Satellite Systems ◽

Processing Strategy ◽

International Gnss Service ◽

Satellite Systems ◽

The World ◽

Product Generation ◽

Clock Correction ◽

Global Navigation Satellite ◽

The Impact

The International GNSS service (IGS) has been providing precise reference products for the Global Navigation Satellite Systems (GNSS) GPS and (starting later) GLONASS since more than 25 years. These orbit, clock correction, coordinate reference frame, troposphere, ionosphere, and bias products are freely distributed and widely used by scientific, administrative, and commercial users from all over the world. The IGS facilities needed for data collection, product generation, product combination, as well as data and product dissemination, are well established. The Center for Orbit Determination in Europe (CODE) is one of the Analysis Centers (AC) contributing to the IGS from the beginning. It generates IGS products using the Bernese GNSS Software.&#160;In the last decade new GNSS (European Galileo and Chinese BeiDou) and regional complementary systems to GPS (Japanese QZSS and Indian IRNSS/NAVIC) were deployed. The existing GNSS are constantly modernized, offering - among others - more stable satellite clocks and new signals. The exploitation of the new data and their integration into the existing IGS infrastructure was the goal of the Multi-GNSS EXtension (MGEX) when it was initiated in 2012. CODE has been participating in the MGEX with its own orbit and clock solution from the beginning. Since 2014 CODE&#8217;s MGEX (COM) contribution considers five GNSS, namely GPS, GLONASS, Galileo, BeiDou2 (BDS2), and QZSS. We provide an overview of the latest developments of the COM solution with respect to processing strategy, orbit modelling, attitude modelling, antenna calibrations, handling of code and phase biases, and ambiguity resolution. The impact of these changes on the COM products will be discussed.&#160;Recent assessment showed that especially the Galileo analysis within the MGEX has reached a state of maturity, which is almost comparable to GPS and GLONASS. Based on this finding the IGS decided to consider Galileo in its third reprocessing campaign, which will contribute to the next ITRF. Recognizing the demands expressed by the GNSS community, CODE decided in 2019 to go a step further and consider Galileo also in its IGS RAPID and ULTRA-RAPID reference products. We summarize our experiences from the first months of triple-system (ULTRA)-RAPID analysis including GPS, GLONASS, and Galileo. Finally we provide an outlook of CODE&#8217;s IGS analysis with the focus on the new GNSS.

Download Full-text

Space weather: risk factors for Global Navigation Satellite Systems

Solar-Terrestrial Physics ◽

10.12737/stp-72202104 ◽

2021 ◽

Vol 7 (2) ◽

pp. 28-47

Author(s):

Vladislav Demyanov ◽

Yury Yasyukevich

Keyword(s):

Space Weather ◽

Solar Radio ◽

Global Navigation Satellite Systems ◽

Navigation Satellite ◽

Satellite Systems ◽

Radio Navigation ◽

Weather Events ◽

Global Navigation Satellite ◽

The Impact ◽

Extreme Space Weather Events

Extreme space weather events affect the stability and quality of the global navigation satellite systems (GNSS) of the second generation (GPS, GLONASS, Galileo, BeiDou/Compass) and GNSS augmentation. We review the theory about mechanisms behind the impact of geomagnetic storms, ionospheric irregularities, and powerful solar radio bursts on the GNSS user segment. We also summarize experimental observations of the space weather effects on GNSS performance in 2000–2020 to confirm the theory. We analyze the probability of failures in measurements of radio navigation parameters, decrease in positioning accuracy of GNSS users in dual-frequency mode and differential navigation mode (RTK), and in precise point positioning (PPP). Additionally, the review includes data on the occurrence of dangerous and extreme space weather phenomena and the possibility for predicting their im- pact on the GNSS user segment. The main conclusions of the review are as follows: 1) the positioning error in GNSS users may increase up to 10 times in various modes during extreme space weather events, as compared to the background level; 2) GNSS space and ground segments have been significantly modernized over the past decade, thus allowing a substantial in- crease in noise resistance of GNSS under powerful solar radio burst impacts; 3) there is a great possibility for increasing the tracking stability and accuracy of radio navigation parameters by introducing algorithms for adaptive lock loop tuning, taking into account the influence of space weather events; 4) at present, the urgent scientific and technical problem of modernizing GNSS by improving the scientific methodology, hardware and software for monitoring the system integrity and monitoring the availability of required navigation parameters, taking into account the impact of extreme space weather events, is still unresolved.

Download Full-text

Comparison of GNSS integrated water vapor and NWM reanalysis data over Central and South America

10.5194/angeo-2019-20 ◽

2019 ◽

Author(s):

Laura Isabel Fernández ◽

Amalia Margarita Meza ◽

María Paula Natali ◽

Clara Eugenia Bianchi

Keyword(s):

Water Vapor ◽

South America ◽

Reanalysis Data ◽

Global Navigation Satellite Systems ◽

Critical Height ◽

Satellite Systems ◽

The Mean ◽

Global Navigation Satellite ◽

Analysis Models

Abstract. We compared and analyzed data of vertically Integrated Water Vapor (IWV) from two different re-analysis models (ERA-Interim from ECMWF and MERRA-2 from NASA's Global Modeling and Assimilation Office) with respect to IWV values from Global Navigation Satellite Systems (GNSS) at 53 stations of Central and South America during the 7-year period from January 2007 till December 2013. The comparison was performed taking into account the geopotential height differences between each GNSS station and the correspondent values assigned by the models. Thus, the set of GNSS stations was divided into 3 groups: Small, Large and Critical height difference stations. Moreover, the performance of the re-analysis models was also analyzed by using an additional classification of three levels according to the mean IWV (IWV) value expected at the station: IWV > 30 kg m−2, 12 kg m−2 &leqslant; IWV &leqslant; 30 kg m−2 and IWV

Download Full-text

The Potential Impact of GNSS/INS Integration on Maritime Navigation

Journal of Navigation ◽

10.1017/s0373463307004614 ◽

2008 ◽

Vol 61 (2) ◽

pp. 221-237 ◽

Cited By ~ 12

Author(s):

Terry Moore ◽

Chris Hill ◽

Andy Norris ◽

Chris Hide ◽

David Park ◽

...

Keyword(s):

Field Trials ◽

Global Navigation Satellite Systems ◽

Navigation Systems ◽

Inertial Navigation Systems ◽

Satellite Systems ◽

Time Period ◽

Maritime Navigation ◽

The Uk ◽

Global Navigation Satellite ◽

The Impact

A version of this paper was presented at ENC-GNSS 2007, Geneva. Its reproduction was kindly authorised by the ENC-GNSS 07 Paper Selection Committee.The General Lighthouse Authorities of the UK & Ireland commissioned an assessment of the impact that the integration of Global Navigation Satellite Systems (GNSS) with Inertial Navigation Systems (INS) would have on the aids to navigation (AtoN) services currently provided, and those to be provided in the future. There is concern about the vulnerability of GNSS, and the provision of complementary and backup systems is seen to be of great importance. The integration of INS could provide an independent and self-contained navigation system, for a limited time period, invulnerable to external intentional or unintentional interference, or the influences of changes in national policies. The study included an analysis of the potential use of GNSS-INS in three of the four phases of a vessel's voyage: coastal, port approach and docking. The project consisted of a technology assessment, looking at the different inertial technologies that might be suitable for each phase. This was followed by a technology proving stage, evaluating suitable equipment using simulation and field trials to prove that the claimed performance could be achieved in practice. The final stage of the project was to assess the effects of the availability of such systems on existing and planned aids to navigation services.

Download Full-text

Performance of GPS Positioning in the Presence of Irregularities in the Auroral and Polar Ionospheres during EISCAT UHF/ESR Measurements

Remote Sensing ◽

10.3390/rs13234798 ◽

2021 ◽

Vol 13 (23) ◽

pp. 4798

Author(s):

Habila Mormi John ◽

Biagio Forte ◽

Ivan Astin ◽

Tom Allbrook ◽

Alex Arnold ◽

...

Keyword(s):

Global Navigation Satellite Systems ◽

Positioning Error ◽

Satellite Systems ◽

Gps Positioning ◽

Transient Nature ◽

Radio Signals ◽

E Region ◽

Global Navigation Satellite ◽

The Impact ◽

Residual Errors

Irregularities in the spatial distribution of ionospheric electron density introduce temporal fluctuations in the intensity and phase of radio signals received from Global Navigation Satellite Systems (GNSS). The impact of phase fluctuations originating from irregularities in the auroral and polar ionospheres on GPS positioning was investigated on three days in March 2018 in the presence of quiet-to-moderately disturbed magnetic conditions by combining measurements from GPS and EISCAT UHF/ESR incoherent scatter radars. Two different positioning solutions were analysed: broadcast kinematic (BK) and precise static (PS). The results show that the propagation through irregularities induced residual errors on the observables leading to an increase in the positioning error, in its variability, and in the occurrence of gaps. An important aspect emerging from this study is that the variability of the 3-D positioning error was reduced, and the presence of gaps disappeared when the positioning solutions were evaluated at a 1 s rate rather than at a 30 s rate. This is due to the transient nature of residual errors that are more significant over 30 s time intervals in the presence of irregularities with scale size between few kilometres in the E region to few tens of kilometres in the F region.

Download Full-text

Earth Orientation Parameter Estimation by Integrating VLBI and GNSS on the Observation Level

10.5194/egusphere-egu21-616 ◽

2021 ◽

Author(s):

Jungang Wang ◽

Kyriakos Balidakis ◽

Maorong Ge ◽

Robert Heinkelmann ◽

Harald Schuh

Keyword(s):

Polar Motion ◽

Reference Frames ◽

Global Navigation Satellite Systems ◽

Satellite Systems ◽

Earth Orientation ◽

Long Baseline ◽

Space Geodetic Techniques ◽

Global Navigation Satellite ◽

The Impact ◽

Globally Distributed

The terrestrial and celestial reference frames are linked by the Earth Orientation Parameters (EOP), which describe the irregularities of the Earth's rotation and are determined by the space geodetic techniques, namely, Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). The satellite geodetic techniques (SLR, GNSS, and DORIS) cannot determine the UT1-UTC or celestial pole offsets (CPO), rendering VLBI the only technique capable of determining full EOP set. On the other hand, the GNSS technique provides precise polar motion estimates due to the continuous observations from a globally distributed network. Integrating VLBI and GNSS provides the full set of EOP and guarantees a superior accuracy than any single-technique solution.In this study we focus on the integrated estimation of the full EOP set from GNSS and VLBI. Using five VLBI continuous observing campaigns (CONT05&#8211;CONT17), the GNSS and VLBI observations are processed concurrently in a common least-squares estimator. The impact of applying global ties (EOP), local ties, and tropospheric ties, and combinations thereof is investigated. The polar motion estimates in integrated solution are dominated by the huge GNSS observations, and the accuracy in terms of weighted root mean squares (WRMS) is ~40&#160;&#956;as compared to the IERS 14 C04 product, which is much better than that of the VLBI-only solution. The UT1-UTC and CPO in the integrated solution also show slight improvement compared to the VLBI-only solution. Moreover, the CPO agreement between the two networks in CONT17, i.e., the VLBA and IVS networks, shows an improvement of 20% to 40% in the integrated solution with different types of ties applied.

Download Full-text

Dynamically Adjusting Filter Gain Method for Suppressing GNSS Observation Outliers in Integrated Navigation

Journal of Navigation ◽

10.1017/s0373463318000334 ◽

2018 ◽

Vol 71 (6) ◽

pp. 1396-1412 ◽

Cited By ~ 2

Author(s):

Lihui Wang ◽

Kangyi Zhi ◽

Bin Li ◽

Yuexin Zhang

Keyword(s):

Inertial Navigation System ◽

Normal Values ◽

External Environment ◽

Processing Method ◽

Global Navigation Satellite Systems ◽

Integrated Navigation ◽

Satellite Systems ◽

Loosely Coupled ◽

Global Navigation Satellite ◽

The Impact

Global Navigation Satellite Systems (GNSSs) are easily influenced by the external environment. Signals may be lost or become abnormal thereby causing outliers. The filter gain of the standard Kalman filter of a loosely coupled GNSS/inertial navigation system cannot change with the outliers of the GNSS, causing large deviations in the filtering results. In this paper, a method based on a χ2-test and a dynamically adjusting filter gain method are proposed to detect and separately to suppress GNSS observation outliers in integrated navigation. An indicator of an innovation vector is constructed, and a χ2-test is performed for this indicator. If it fails the test, the corresponding observation value is considered as an outlier. A scale factor is constructed according to this outlier, which is then used to lower the filter gain dynamically to decrease the influence of outliers. The simulation results demonstrate that the observation outlier processing method does not affect the normal values under normal circumstances; it can also discriminate between single and continuous outliers without errors or omissions. The impact time of outliers is greatly reduced, and the system performance is improved by more than 90%. Experimental results indicate that the proposed methods are effective in suppressing GNSS observation outliers in integrated navigation.

Download Full-text