scholarly journals Towards operational multi-GNSS tropospheric products at GFZ Potsdam

2021 ◽  
Author(s):  
Karina Wilgan ◽  
Galina Dick ◽  
Florian Zus ◽  
Jens Wickert
Keyword(s):  
Positive Impact ◽  
Weather Forecast ◽  
Forecast Model ◽  
Global Navigation Satellite Systems ◽  
Three Solutions ◽  
Satellite Systems ◽  
Weather Forecasts ◽  
Preparation Step ◽  
Global Navigation Satellite ◽  
The Impact

Abstract. The assimilation of Global Navigation Satellite Systems (GNSS) data has been proven to have a positive impact on the weather forecasts. However, the impact is limited due to the fact that solely the Zenith Total Delays (ZTD) or Integrated Water Vapor (IWV) derived from the GPS satellite constellation are utilized. Assimilation of more advanced products, such as Slant Total Delays (STDs) from more satellite systems may lead to improved forecasts. This study shows a preparation step for the assimilation, i.e. the analysis of the multi-GNSS tropospheric advanced parameters: ZTDs, tropospheric gradients and STDs. Three solutions are taken into consideration: GPS-only, GPS/GLONASS (GR) and GPS/GLONASS/Galileo (GRE). The parameters are compared with two global Numerical Weather Models (NWM): European Centre for Medium Weather Forecast (ECMWF) ERA5 reanalysis and a forecast model ICON run by the German Weather Service. The results show that for ZTDs and horizontal gradients, all three GNSS solutions show similar level of agreement with the NWM data. For ZTDs, the agreement is better for the ERA5 model with biases of approx. 1.5 mm and standard deviations (SDs) of 7.7 mm than for ICON with biases of 3.2 mm and SDs of 10 mm. For tropospheric gradients, the agreement with both NWMs is very similar: the biases are negligible and SDs equal to approx. 0.4 mm. For the STDs, the GPS-only solution has an average bias w.r.t. ERA5 of 4.2 mm with SDs of 25.2 mm. The statistics are very slightly reduced for the GRE solution and further reduced to a bias of 3.5 mm with SDs of 24.5 mm for the Galileo-only observations. This study shows that all systems are of comparable quality. However, the advantage of combining more GNSS systems in the operational data assimilation is the geometry improvement by adding more observations, especially for low elevation angles.

scholarly journals Towards operational multi-GNSS tropospheric products at GFZ Potsdam

2022 ◽  
Vol 15 (1) ◽  
pp. 21-39
Author(s):  
Karina Wilgan ◽  
Galina Dick ◽  
Florian Zus ◽  
Jens Wickert
Keyword(s):  
Positive Impact ◽  
Satellite System ◽  
Three Solutions ◽  
Satellite Systems ◽  
Weather Forecasts ◽  
Preparation Step ◽  
Global Navigation Satellite ◽  
Gnss Data ◽  
The Impact ◽  
Comparable Quality

Abstract. The assimilation of global navigation satellite system (GNSS) data has been proven to have a positive impact on weather forecasts. However, the impact is limited due to the fact that solely the zenith total delays (ZTDs) or integrated water vapor (IWV) derived from the GPS satellite constellation are utilized. Assimilation of more advanced products, such as slant total delays (STDs), from several satellite systems may lead to improved forecasts. This study shows a preparation step for the assimilation, i.e., the analysis of the multi-GNSS tropospheric advanced parameters: ZTDs, tropospheric gradients and STDs. Three solutions are taken into consideration: GPS-only, GPS–GLONASS (GR) and GPS–GLONASS–Galileo (GRE). The GNSS estimates are calculated using the operational EPOS.P8 software developed at GFZ. The ZTDs retrieved with this software are currently being operationally assimilated by weather services, while the STDs and tropospheric gradients are being tested for this purpose. The obtained parameters are compared with the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis. The results show that all three GNSS solutions show similar level of agreement with the ERA5 model. For ZTDs, the agreement with ERA5 results in biases of approx. 2 mm and standard deviations (SDs) of 8.5 mm. The statistics are slightly better for the GRE solution compared to the other solutions. For tropospheric gradients, the biases are negligible, and SDs are equal to approx. 0.4 mm. The statistics are almost identical for all three GNSS solutions. For STDs, the agreement from all three solutions is very similar; however it is slightly better for GPS only. The average bias with respect to ERA5 equals approx. 4 mm, with SDs of approx. 26 mm. The biases are only slightly reduced for the Galileo-only estimates from the GRE solution. This study shows that all systems provide data of comparable quality. However, the advantage of combining several GNSS systems in the operational data assimilation is the geometry improvement by adding more observations, especially for low elevation and azimuth angles.

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

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
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.

scholarly journals CODE IGS reference products including Galileo

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

<p>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.</p><p> </p><p>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’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.</p><p> </p><p>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’s IGS analysis with the focus on the new GNSS.</p>

scholarly journals Space weather: risk factors for Global Navigation Satellite Systems

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.

Impact of the Different Components of 4DVAR on the Global Forecast System of the Meteorological Service of Canada

2007 ◽  
Vol 135 (6) ◽  
pp. 2355-2364 ◽  
Author(s):  
Stéphane Laroche ◽  
Pierre Gauthier ◽  
Monique Tanguay ◽  
Simon Pellerin ◽  
Josée Morneau
Keyword(s):  
Data Assimilation ◽  
Positive Impact ◽  
Weather Forecast ◽  
Forecast Model ◽  
Variational Data Assimilation ◽  
Global Forecast System ◽  
Forecast System ◽  
Medium Range Weather Forecast ◽  
Medium Range ◽  
The Impact

Abstract A four-dimensional variational data assimilation (4DVAR) scheme has recently been implemented in the medium-range weather forecast system of the Meteorological Service of Canada (MSC). The new scheme is now composed of several additional and improved features as compared with the three-dimensional variational data assimilation (3DVAR): the first guess at the appropriate time from the full-resolution model trajectory is used to calculate the misfit to the observations; the tangent linear of the forecast model and its adjoint are employed to propagate the analysis increment and the gradient of the cost function over the 6-h assimilation window; a comprehensive set of simplified physical parameterizations is used during the final minimization process; and the number of frequently reported data, in particular satellite data, has substantially increased. The impact of these 4DVAR components on the forecast skill is reported in this article. This is achieved by comparing data assimilation configurations that range in complexity from the former 3DVAR with the implemented 4DVAR over a 1-month period. It is shown that the implementation of the tangent-linear model and its adjoint as well as the increased number of observations are the two features of the new 4DVAR that contribute the most to the forecast improvement. All the other components provide marginal though positive impact. 4DVAR does not improve the medium-range forecast of tropical storms in general and tends to amplify the existing, too early extratropical transition often observed in the MSC global forecast system with 3DVAR. It is shown that this recurrent problem is, however, more sensitive to the forecast model than the data assimilation scheme employed in this system. Finally, the impact of using a shorter cutoff time for the reception of observations, as the one used in the operational context for the 0000 and 1200 UTC forecasts, is more detrimental with 4DVAR. This result indicates that 4DVAR is more sensitive to observations at the end of the assimilation window than 3DVAR.

The Potential Impact of GNSS/INS Integration on Maritime Navigation

2008 ◽  
Vol 61 (2) ◽  
pp. 221-237 ◽  
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.

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

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.

scholarly journals A multi-sensor satellite-based archive of the largest SO<sub>2</sub> volcanic eruptions since 2006

2020 ◽  
Author(s):  
Pierre-Yves Tournigand ◽  
Valeria Cigala ◽  
Elzbieta Lasota ◽  
Mohammed Hammouti ◽  
Lieven Clarisse ◽  
...  
Keyword(s):  
Volcanic Eruptions ◽  
Weather Forecast ◽  
Global Navigation Satellite Systems ◽  
Orthogonal Polarization ◽  
Vertical Column ◽  
Satellite Systems ◽  
Aviation Management ◽  
Vertical Column Density ◽  
High Consistency ◽  
Global Navigation Satellite

Abstract. We present a multi-sensor archive collecting spatial and temporal information about volcanic SO2 clouds generated by the eleven largest eruptions of this century. The detection and monitoring of volcanic clouds is an important topic for aviation management, climate issues and weather forecast. Several papers have been published focusing on single events, but not any archive is available at the moment to be used as background for future studies. We archived and collocated the SO2 vertical column density estimations from three different instruments (AIRS, IASI and GOME-2), the atmospheric parameters vertical profiles from the Global Navigation Satellite Systems (GNSS) Radio Occultations (RO) and the vertical backscatter from the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP). We additionally provide information about the cloud top height from three different algorithms and the atmospheric anomaly due to the presence of the cloud. The dataset consists of 223 days monitored with SO2 clouds, collocated with 56675 backscatter profiles and 70126 radio occultation profiles. The modular structure of the archive allows an easy collocation of the different datasets according to the users’ needs and the cross-comparison of the datasets shows the high consistency of the parameters estimated with different sensors and algorithms. The data described here will be published with a DOI after final acceptance of this manuscript (Tournigand et al., 2020, http://doi.org/10.5880/fidgeo.2020.016). During the discussion period, the data are accessible via this temporary link: http://pmd.gfz-potsdam.de/panmetaworks/review/0f85d699707efcdc567765bd0dafaaadf94b6df5a531f310167f7e974ea803bf

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

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

&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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&amp;#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&amp;#160;&amp;#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.&lt;/p&gt;

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

2018 ◽  
Vol 71 (6) ◽  
pp. 1396-1412 ◽  
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.

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