National Geographic Institute of Spain (IGNE) is Analysis Center of EUREF since 2001, carrying out weekly and daily processes of a subnetwork of GNSS permanent stations covering mainly the Western Europe part (Spain, Portugal, France, Italy, Great Britain, Ireland...). This processing is focused on contributing to the definition, realization and maintenance of the European Geodetic Reference System.

Since then, new GNSS data processing projects have emerged, not only those who require a punctual processing, but others requiring continuous solutions. In some of them a network of more than 330 stations is processed. The objectives of these projects are not only the obtaining of coordinates of GNSS permanent stations, but also other objectives such as obtaining and analyzing geodynamic time series or calculating in almost-real time the tropospheric delay signal for meteorological applications.

The latest advances in GNSS, especially the addition of Galileo to the Global GNSS constellations and the upgrade of some receivers to multi-constellation devices, have made possible to include Galileo observations in the data processing. A test campaign, using Bernese 5.2 software, was carried out with the objective of evaluating the impact of including these observables in the solution. Other parameters, such us the network configuration, have been tested in the campaign in order to reach the optimal processing strategy.

A description of the different projects and the results obtained in the Galileo test campaign are presented.

A software-defined receiver, known as FGI-GSRx, has been developed in the Finnish Geospatial Research In-stitute (FGI) over the years for analyzing and validating the research findings in the context of multi-frequency multi-GNSS constellation. The FGI-GSRx is capable of processing signals from five different sys-tems, namely GPS, GLONASS, Galileo, BeiDou and IRNSS/NAVIC. The development of FGI-GSRx software-defined receivers have been published in different forums, where performance of different GNSS signals, specifically, for GPS L1, Galileo E1, GLONASS L1, IRNSS L5 and BeiDou B1 and B2, are reported with live real data and simulated signals. In this work, the authors describe the implementation of Galileo E5a and Galileo E5b signals, address some implementation challenges due to the existence of secondary codes, and then finally compare the performance of these new signals with the existing L1/E1 signals via real live signal.

A triple-band GTEC radio Front-End (FE) from Teleorbit is used to capture the real GNSS data. The first FE is configured to receive GPS L1 and Galileo E1 signal, the second FE is configured to receive Galileo E6 signal, and the third FE is configured to receive Galileo E5a and Galileo E5b signal. The first FE has a bandwidth of 38 MHz with sampling frequency 40.5 MHz, while the third FE has a bandwidth of 54 MHz with a sampling frequency of 81 MHz. The FGI-GSRx is designed to process each individual signal separately with the specified FE configuration. It thus facilitates processing of Galileo E5a and E5b signals, separately. The multi-GNSS configuration is designed such that the user could flexibly decide on the number of constellations he/she would like to consider for position computation. It is important also to mention that the receiver treats each frequency component of a single system separately.

The GNSS data was collected on January 04, 2019 at around 16:10 UTC time at a static position with a roof antenna in FGI, Finland. The FGI-GSRx receiver can acquire, track and compute a navigation solution with the visible Galileo satellites. The stand-alone positioning results with Galileo E1, E5a, and E5b will be presented followed by GPS-only and multi-GNSS positioning results with different combinations of Galileo and GPS signals.

In the single point static position solution, there are 5 Galileo E5 satellites used in the position fix. The horizontal and vertical RMS values with 5 Galileo satellites are about 0.62 meters and 0.56 meters, respectively. The 95% error for horizontal and vertical directions are about 0.93 meters and 0.73 meters, respectively. The position fix is computed at a 10 Hz rate. Ne-Quick ionospheric model is applied to each individual frequency. Saastamoinen model is also applied to get rid of tropospheric error. A comparison of performance between FGI-GSRx software-defined receiver and the open source receiver 'GNSS-SDR' based on GNU-radio toolkit will also be presented for the same data set. The significance of this study is to present the implementation details of a Galileo E5a/E5b receiver along with a first-hand overview of the expected performance of Galileo E5a/E5b live signal.

Travelling ionospheric disturbances (TIDs), wavelike perturbations in ionospheric parameters, are one of the most common ionospheric disturbances that affect Global Navigation Satellite System (GNSS) precise positioning algorithms, such as Real-Time Kinematic (RTK) approaches relying on accurate ionospheric models. For this reason, it is important to develop algorithms for accurate observation and detection of TIDs.
Dense networks of receivers are available from GNSS, such as Galileo and the American Global Positioning System (GPS), and they provide powerful ionospheric sensors. The extensive coverage of such networks makes GNSS an especially valuable tool for studying large scale TIDs (LSTIDs), which can travel over very large distances. However, this is not entirely without drawbacks, as the movement of the satellites in conjunction with the movement of the TID itself complicates the evaluation of the wave parameters.
A case study is presented of a LSTID passing over North America during the third day of a series of geomagnetic storms on 29-31 October 2003. The LSTID is imaged in time-varying three-dimensional free electron density using the MIDAS (Multi-Instrument Data Analysis System) ionospheric tomography algorithm and GPS Total Electron Content (TEC) measurements from a large number of receivers. The observed TID has a southeasterly direction, an estimated wavelength of around 800 km, an estimated period of ca 30 minutes and causes TEC perturbations of around 4%.
In order to validate the imaging results, the estimated TID characteristics are then fed into a physics-based TID model which is used to recreate synthetic TEC measurements. The MIDAS results generated from these measurements are in turn compared to the real data MIDAS images to validate the process end-to-end.
The challenges of TID imaging and the evaluation of the TID parameters using GNSS are discussed. Finally, the results of the case study are used to exemplify the effects on GNSS positioning, and potential mitigation methods are discussed.

Global Navigation Satellite Systems (GNSS) are an effective tool for monitoring the Earth’s ionospheric activity by measuring its total electron content (TEC). Ionospheric delays derived from the GNSS signals can be used not only for studying the properties of the ionosphere, but also to enhance the estimation of other GNSS based products such as receiver coordinates, satellite orbits, and tropospheric delays. Traditionally, the geometry-free linear combinations of dual-frequency GNSS data, potentially combined with a phase-to-code leveling strategy, are often used as ionospheric observables. Since these are biased by either the differential code biases or the carrier-phase ambiguities, unbiased TEC estimates can only be obtained through an external model that describes the temporal and spatial TEC distribution.
In this study, we use the undifferenced and uncombined GNSS code and carrier-phase measurements on two or more frequencies rather than their geometry-free combinations. A full rank observation model is formed through a proper choice of the estimable parameters. This resolves the inherent limitations and disadvantages of the geometry-free approach, namely: We are not restricted to only two frequencies; the geometry terms are not canceled and can therefore be further parameterized into receiver positions, clocks, and tropospheric delays, thus strengthening the underlying system model; the original carrier-phase ambiguities on each frequency are preserved, so that the respective double-difference ambiguities can be resolved and the high precision of the carrier-phases can be fully exploited; we keep the full redundancy of the observation model.
We analyze the precision of the TEC estimates using a local setup centered in Germany with a polynomial TEC model. The results using a single GNSS receiver, a local array of receivers, and a regional network of IGS stations are analyzed and compared. In particular, the role played by parameterizing the geometry terms and the relevance and impact of carrier-phase integer ambiguity resolution for TEC determination are investigated. We demonstrate why and by how much the precision of the single station TEC solution is improved by array and, much more so, by network solutions. This implies that the relatively long convergence times required for high-precision TEC determination can be clearly reduced. The results are verified through an analysis of the convergence times of a long-baseline RTK positioning example.

For twenty-five years, the International Global Navigation Satellite System (GNSS) Service (IGS) has carried out its mission to advocate for and provide freely and openly available high-precision GNSS data and products. IGS was first approved by its parent organization, the International Association of Geodesy (IAG), at a scientific meeting in Beijing, China, in August of 1993. A quarter century later, the IGS community gathered for a workshop in Wuhan, China to blaze a path to Multi-GNSS through global collaboration.

The IGS is a critical component of the IAG’s Global Geodetic Observing System (GGOS), where it facilitates cost-effective geometrical linkages with and among other precise geodetic observing techniques, including: Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS). These linkages are fundamental to generating and accessing the International Terrestrial Reference Frame (ITRF). As it enters its second quarter-century, the IGS is evolving into a truly multi-GNSS service, and at its heart is a strong culture of sharing expertise, infrastructure, and other resources for the purpose of encouraging global best practices for developing and delivering GNSS data and products all over the world.

This poster will present an update on current IGS products and operations, as well as highlights on recent organizational developments and community activities. The impacts and benefits of global cooperation and openly available data will be emphasized, and information about the IGS stations and network, contributions to the International Terrestrial Reference Frame solutions, and product applications will be presented. A summary of IGS products, in particular how they are made, and their availability will be provided. Outcomes of the 2018 Wuhan Workshop, future technical challenges, and potential new directions will be discussed.

At the end of 2016 the European Commission has declared the Galileo Initial Services. The declaration means that the Galileo satellites and ground infrastructure are operational and ready for positioning, navigation and timing on the way to full operational capability in 2020.

Galileo performance monitoring plays a important role for testing and verifying the initial services and to ensure the provision of high quality satellite data to users. One of the key performance indicators (KPI) is the signal-in-space range error (SISRE). SISRE represents the error budget related to the control and space segment of Global Navigation Satellite Systems and can be determined by comparing broadcast against precise ephemerides. The Galileo single point positioning accuracy can be described by the horizontal and vertical position error KPIs. These position related KPIs are derived by comparing single point position solutions against precisely determined reference station coordinates.

We will show current results of the Galileo satellite orbit and clock performance monitoring and Galileo single point positioning performance for selected stations in Northern Europe.

One of the crucial source of biases in GNSS measurements are the phase center variations of the both transmitter and receiver antennas. For high-end applications based on carrier phase measurements, a set of consistent absolute phase center corrections is necessary. The development of new satellite systems such as Galileo and BDS, as well as introduction of new carrier frequencies in GPS and GLONASS, cause the necessity to perform precise calibration of antennas designed for these new signals.
Therefore, ASTRI Polska in cooperation with the University of Warmia and Mazury in Olsztyn started in 2019 the GRAVEr project founded by the European Space Agency (ESA). The purpose of the project is the development and implementation of field calibration procedure for multi-frequency and multi-system GNSS antennas. The methodology and algorithms proposed in GRAVEr are based on “Hanover” concept of absolute field receiver antenna calibration. However, in our approach some innovation will be introduced. First of all our goal is to develop EGNSS receiver antenna calibration procedure for Galileo multi-frequency signals. Nevertheless we are also aiming at calibrations for other systems like GPS, GLONASS and BDS. During project realization we will also evaluate alternative approaches for the phase center variations’ modeling. Aside of commonly used spherical harmonics expansion, we will also use spline functions or least-squares collocation method. The presentation show the current status of the activity.

The Geodetic Observatory Pecny (GOP) has recently implemented a generation of precise orbit and clock products in order to support Galileo Reference Center (GRC), available in two rapid modes - 12h and 42h delays. A procedure of multi-GNSS orbit determination has been implemented using the Bernese GNSS software V52 and double-difference solution in a global network. The clock corrections are completed using a new in-house software (G-Nut/Sothis) and a strategy of combining undifferrenced pseudoranges and epoch-difference phase observations. Additionally, a service for providing consolidated and quality controlled daily global navigation files has been developed using parameter range checks, time-series analysis and statistical assessments. An operational real-time clock corrections estimation was also developed for GPS and Galileo in Europe including a new robust clock datum definition and initial clock bias connections, both aimed particularly for the applied mixed-difference strategy and real-time regional-based product. Status of the precise orbit and clock product quality, and the results of the precise real-time analyses in a regional network are presented.

SCER (Secure Code Estimation and Replay) spoofing techniques represent a severe threat to modern GNSS systems, even for those providing its users with defense and counteracting methods based on Navigation Message Authentication (NMA). Due to the risk this type of spoofing techniques pose for modern GNSS systems it is essential to characterize in detail the feasibility of such kinds of attacks in realistic contexts, allowing the proposal of additional defense techniques for GNSS users. Although the SCER spoofing attacks are widely covered in the literature, perfect Acquisition and Tracking stages are considered by some of the authors. Moreover, the impact due to a realistic channel response in the spoofer symbol estimation is typically not found.

This paper provides with a detailed review of the impact over SCER spoofers due to errors in the estimation of time delay and Doppler shift. It also considers the channel influence on the spoofer symbol estimation through generative models to adequately characterize the channel behavior for the attacker. The channel modeling step allows approaching the SCER spoofer issue more realistically as time series responses can be simulated and analyzed. This work considers different channel behaviors that may affect future GNSS applications like autonomous cars.

In a second stage, a set of recommendations is derived for GNSS receiver manufacturers. Based on Data Mining techniques, this paper analyzes possible methods to detect the spoofer presence: First, data reduction techniques are considered (PCA). Then, Signal features at the acquisition stage are used to train data mining algorithms covering different classifiers (Neural Networks, decision trees, Gaussian Mixture Models and Support Vector Machines) to help the GNSS users to detect the attack.

Other complementary simple solutions are applied to detect bursting or chirping signals, which can be used by the spoofer to get the victim receiver out of lock before starting the attack. Such initial detection can also be used to provide further inputs to the data mining classifiers, providing an extra contribution to the victim’s protection system. This step may help to reduce the false alarm rates of the protection system (i.e., it is not likely that multipath signals will be preceded by RFI events, although we can expect advance SCER spoofers to try first to blind the victim).

Several signal metrics, combined with the techniques described above, are analyzed providing final users with a set of recommended methods for spoofing protection against SCER attacks on NMA.
A brief introduction is provided to the workbench designed in Python to simulate the SCER attacks on the Galileo OS-NMA. This setup allows the generation of I/Q samples signal records at different stages: at the spoofer receiver input or at the victim receiver input (therefore the structure enables the generation of a SCER satellite spoofed scenario). This workbench allows the benchmarking of different spoofer estimation techniques and the defense techniques for the victim’s receiver.
The workbench is highly modular, allowing the quick evaluation of new detection and symbol estimation algorithms.

GNSS are widely used for positioning, navigation and timing (PVT). The quality of results depends on the antenna in use and the capability to take antenna specific effects into account. The most prominent corrections are the direction dependent phase center corrections (PCC), which include corrections for the phase center offset (PCO) and the phase center variations (PCV). These corrections range between a few up to several millimeters for carrierphase observations and up to some decimeters for code observations. In addition, the magnitude of the error depends on the used antenna type and can differ even for different antennas of the same type and manufacturer
The frequency-dependent PCC are either determined in an anechoic chamber or in the field using a robot (so-called absolute field calibration). Both methods have their advantages and drawbacks. In the Antenna Exchange Format (ANTEX) from the International GNSS Service (IGS), which is widely used, currently only PCC for L1- and L2 frequencies for GPS and GLONASS are officially published. Absolute field calibrations values for new signals like Galileo or GPS L5 are missing. Only some chamber calibration results are available in the European Permanent Network (EPN).
The Institute für Erdmessung (IfE) is one of the the IGS accepted absolute field calibration institutions and provides PCC using the so-called Hannover-Concept. In this approach a robot is used to precisely rotate and tilt the antenna under test. This concepts has now been extended to an experimental approach. The PCC of new signals are estimated in post-processing as spherical harmonics using time differenced single differences. First results show both – a high repeatability of the estimated pattern and an improvement on the observation domain.
In this contribution the theoretical background as well as the extended concept are described. Moreover, patterns for Galileo signals and GPS L5 will be shown and discussed. After a short introduction into the method and the extended Hannover-Concept the robot model and the adjustment concept will be presented. The contribution will show that the estimation of PCC for Galileo signals is feasible with the developed method. This can be described by the root mean square (RMS) of differential pattern (of different calibrations). This indicator for the repeatability show RMS values for the EL1X signal under 0.6 mm for the NOV703GGG antenna and under 0.4 mm for the LEIAR25.R3. The RMS for the EL5X signal is maximal 0.6 mm for the NOV703GGG or 0.65 mm for the LEIAR25.R3. Furthermore, the obtained patterns will be presented and discussed for several antennas typical to IGS stations. For instance the PCV of the LEIAR25.R3 show values in a range of -4 to 7 mm for the EL1X frequency, whereas the Up-component of the PCO is approximately 60 mm. If these PCC are taken into account, the RMS of the single differences (SD) of a short baseline, common clock experiment at the Physikalisch-Technische Bundesanstalt (PTB) can be improved.

The goal of this study is to test the Modified Ambiguity Function Approach (MAFA) method using the Galileo System and GPS. The MAFA is a method of processing GNSS carrier phase observations for precise positioning. This method does not contain the ambiguity resolution step although the integer nature of ambiguities is taken into account using appropriate form of a mathematical model. The theoretical foundations of precise positioning using the MAFA method is presented. The test data consist of GPS and Galileo observations. A self-made software using the MAFA method is applied. The data from five different days is used. Test is divided into two parts. In the first part short static sessions is performed for GPS data only, Galileo data only and for GPS and Galileo data combination. In the second part the data is tested in RTK mode for GPS data only, Galileo data only and for GPS and Galileo data combination.
The obtained results show that the usage of GPS and Galileo combinations allow to increase the precision of the obtained result comparing to GPS only or Galileo only solutions. Results obtained for GPS only and Galileo only are similar in accuracy and precision. The important issue in multisystem data processing is incorporating the Inter System Bias (ISB) - the difference between the receiver hardware delays affecting the signals from different systems.

In this poster, soil moisture monitoring results during 66 continuous tracking days are presented.
The experiment was conducted in the installations of the Cajamar Centre of Experiences, located in Paiporta (Valencia, Spain), which is an agricultural research technology centre.
GNSS-IR is a well-documented technique to infer temporal changes in topsoil moisture for the area surrounding the antenna (scale of about 1000 m²). The novelty of this research is the use of multi-constellation SNR observables (GPS, GLONASS and GALILEO satellites) an the use of simultaneous observations using a geodetic-quality GNSS instrument and a mass-market antenna connected to a Raspberry Pi 3 as a control device and for storing the observations.
5 seconds sample rate observations are obtained for both sensors, so geodetic-quality observations can be used as a control data for the low cost sensor. However, both sensors results have been compared with soil moisture measurements based on soil samples taken at 5 cm depth and weighed in laboratory before and after being dried (gravimetric method).
Low cost sensor uses NMEA GSV sentences to provide integer elevation, azimuth and signal-to-noise ratio (SNR) numbers, which are the basis for the soil moisture determination. Float elevation and azimuth numbers are obtained in post-process from the IGS navigation files.
Based on our results, we can conclude:
a) The integration of all navigation satellite constellations will produce a more homogeneous and dense footprint around the antenna, so different sectors around the antenna can be considered independently for soil moisture monitoring (for example to locate concrete areas with irrigation problems).
b) Low cost sensors can be used, so the technique can be introduced in the agricultural market without excessive cost.

PNT users more and more tend to exploit multiple sensor data to aid Global Navigation Satellite Systems (GNSS) in challenging environmental conditions. The use of camera systems in this field is getting more attention. These sensors represent an added-value by classifying the surroundings of any user in order to analyse whether an observed satellite signal is either line-of-sight (LOS) (i.e. direct path) or non-line-of-sight (NLOS) (i.e. different from the nominal). This classification can be used, among others, to characterize, weight or exclude observations in the process of acquiring position, velocity, and timing (PVT) solutions. This application may be used in, for example, the field of autonomous driving vehicles.

This study, however, focusses on the use a fisheye camera system to assess the availability and reliability of GNSS in challenging environmental scenarios, and therefore characterize the effect of such conditions at user level. To classify satellites as LOS or NLOS, the recorded fisheye camera image needs to be segmented into sky and non-sky regions. Different image segmentation algorithms are assessed which can be roughly classified into image histogram based segmentation techniques and image gradient segmentation techniques. To ensure robustness of segmentation, the different algorithms are benchmarked using a set of reference images for which the segmentation is known a-priori. This set of reference images contains a number of different environments (urban canyon, dense vegetation, and open sky) as well as a number of different weather conditions (sunny, cloudy, and dusk). Although, the image histogram based segmentation is generally able to observe more features, the marker based watershed algorithm (using the image gradient) performs better, especially in sunny conditions (i.e. in which the pixel intensity strongly varies in the sky segment).

The calibration required for the correct mapping of the satellites onto the image is further improved with respect to existing methods. This is accomplished using a genetic algorithm selecting an optimum set of calibration images considering, among others, good coverage of the field-of-view of the camera as well as the image re-projection error. This approach is validated using a static test in which the CN0 for the classified satellites (NLOS or LOS) is assessed.

In addition, the classification of the satellites (provided by the image segmentation algorithm) can be used to filter the observations in the process of obtaining a PVT solution. The resulting positioning improvement is used to validate the correct image segmentation of a complete set of test campaign results.

Using the aforementioned approach, the camera footage of test campaigns in Haarlem (dense vegetation), Rotterdam (urban canyon), and Amsterdam (urban) in the Netherlands are analysed. The classification of the available satellites as either LOS or NLOS gives an estimation on the reliability of GNSS in these different environments. The reliability and availability of GNSS directly relates to the attainable positioning accuracy, among others through the effect on the geometric dilution of precision (GDOP). Therefore, these types of testing can be, for example, used to assign regions in which GNSS augmentation services might be desired.

Atmospheric water vapour is important in the climate feedback process and is a very efficient greenhouse gas. Long-term trends in the atmospheric water vapour is therefore important in climate monitoring. With a relatively high temporal resolution, continuously improving spatial coverage, and less expensive receivers, ground-based GPS networks have been identified as a useful technique to obtain accurate long-term trends in the integrated amount of water vapour (IWV) in the atmosphere.

We have recently studied the impact on the estimated trends by using different elevation cutoff angles in the GPS data processing. This dataset, including 13 GPS sites in Sweden and Finland and covering a 20-year time period, is here used for more detailed studies. For example, using subsets of the data we can separate trends for different seasons and different times of the day. In this region the radiosonde launch times are, typically at 0 h UT and 12 h UT, that are within ± 2 h to the local midnight and noon, respectively.

Trends from the use of two different elevation cutoff angles (10° and 25°) will be studied together with trends from radiosonde data at 7 nearby launching sites, as well as trends derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data (ERA- Interim).

We will compare the different available trends in the IWV with trends in the atmospheric mean temperature, obtained from ERA-Interim, over this 20-year long time period in order to study and quantify the relation between long-term trends in the temperature and the humidity. This relation is important as it determines the level of feedback due to water vapour, acting as a green-house gas, with increasing temperatures in climate modelling. Assuming conservation of relative humidity, the IWV changes are related to a change in the temperature with a ratio of approximately 7 %/K. However, due to the high variability of the humidity and the limited accuracy in the determination of the long-term changes in the IWV, the relation is difficult to validate.

The present study targets to assess the potential use of EGNOS for maritime navigation compliant with the requirements of the International Maritime Organization (IMO) established in its Resolution A.1046 (27). The most demanding IMO requirements for the Maritime Service are established for harbor entrances, harbor approaches and coastal waters. Numerically those requirements are: 99.8% of Signal Availability, 99.8% of Service Availability, Horizontal Accuracy of 10 m (percentile 95th) and 99.97% of Service Continuity over a period of 15 minutes.

Three different types of data have been used in the assessment. First, Availability, Continuity and Service Coverage maps have been computed following a fault-free receiver approach, in which it is assumed a continuous signal tracking, without cycle-slips, all GPS navigation data and EGNOS corrections available, and no environmental effects. Second, the static assessment has used 108 permanent stations located within 20 km of the coast or in islands across the EGNOS coverage area. Third, a kinematic assessment with a vessel from the Armed Institute of the Spanish Civil Guard based in the Canary Island of Tenerife, in the EGNOS south-west border of coverage.

The calculations have been performed with the ESA/UPC GNSS laboratory (gLAB) tool suite. The Availability and Continuity are evaluated within the a simple and preliminary squared geographical region defined within coordinates from -25ºW to 37ºE in longitude and from 25ºN to 77ºN in latitude, in order to perform a quantitative comparison of the different computations. For the static and kinematic accuracy assessments, we have computed a reference position and trajectory using the Precise Point Positioning (PPP) technique and final orbits from the International GNSS Service (IGS). The error of the permanent stations and the vessel is evaluated as the difference in the coordinates obtained with single-frequency EGNOS maritime solution and those obtained with the dual-frequency PPP.

The static test campaign comprised from 01/01/2016 to 30/04/2018, whereas the kinematic campaign started on 06/11/2018 and will last until the end of April 2019. Then, results presented at the time of writing this abstract include until 31st of March of 2019. The EGNOS Maritime Service met the IMO requirements: i) Signal Availability (after reaching 99.999% of the time), ii) Service Availability (covering 68.27% of the predefined rectangular region), and iii) Accuracy (after reaching 1.03 m at the 95th percentile). The EGNOS Service Continuity over 99.97% is achieved in an extensive area of the coastal waters, except in the borders (e.g. very high or very low latitude). In oceanic waters, there is no continuity requirement and the service area there is only limited by the availability requirement.

We conclude that EGNOS is suitable for maritime navigation in coastal and oceanic waters. The continuity risk is, by far, the most limiting factor for expanding the EGNOS Maritime Service along the coastal waters in Europe and, particularly, along the Canary Islands, in the EGNOS south-west border of coverage.

Topic Codes: E06 (Troposphere / climatology); E09 (GNSS remote sensing, GNSS reflectometry)

Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) signals experience delays and distortions because of their propagation in the Earth's atmosphere. Thus, observations of GNSS and InSAR provide valuable contributions for reconstructing the amount of water vapor integrated along the path from the satellites to the observation site on the surface of the Earth. On the one hand, GNSS provides measurements with a high temporal resolution; however due to the sparse density of GNSS ground networks, the spatial resolution is relatively low to provide accurate information about the troposphere everywhere inside the network area. On the other hand, InSAR acquisitions of images with a high density of observations have a low repetition rate of days to weeks only; meanwhile the amount of tropospheric water vapor may have changed completely, and therefore, if not accounted accordingly, the changes in refractivity might be misinterpreted as deformations. This work presents tropospheric delay models retrieved by GNSS, InSAR and their synergic combination.
Initially, tropospheric pathdelays computed by GNSS and InSAR techniques are compared. In this case, difference slant delays (dSTDs) are calculated from GNSS measurements, using zenith total delays (ZTDs) collocated and interpolated in the least squares software COMEDIE (Collocation of Meteorological Data for Interpretation and Estimation of Tropospheric Pathdelays). This dSTDs are compared with InSAR estimated dSTDs. For most of the InSAR interferograms the results show a good agreement between the two techniques. However, there are days of InSAR acquisition for which the agreement between the two datasets are poor. After investigations, the main reason that was figured out for this poor agreement was the low variability of the troposphere, reflected in standard deviations of GNSS dSTDs. Furthermore, measurements of the two techniques are combined together with the goal to have a better retrieval of the atmospheric water vapor than each technique individually. Indeed, their complementary characteristics in terms of resolution can be exploited and the combined product can be used for assimilation in numerical weather prediction (NWP) models. A millimeter level accuracy is achieved in the latter case, while an improvement is reported when observations from both sensors are used. In this case, the comparison is performed in terms of ZTDs for a set of simulated measurements, as well as in terms of dSTDs for real measurements.
The area of investigation is the Alpine region in Switzerland. A set of simulated data and a set of real data are used for this work. InSAR acquisitions, for a period of 5 years, from COSMO-SkyMed satellite are used as interferometric measurements, whilst measurements from the Federal Office of Topography GNSS Network were available with an hourly temporal resolution as GNSS measurements. Moreover, tests based on synthetic measurements were as well performed. The simulated measurements (for GNSS and InSAR) were generated from COSMO-1, the NWP model deployed by MeteoSwiss. Estimated tropospheric models at COSMO-1 grid coordinates were directly compared with the ZTDs calculated from COSMO-1.

In 2019 the European Global Navigation Satellite System (GNSS) Galileo has reached its full operational capability. Meanwhile the full 24 satellite constellation is available to the users. The use of the Galileo signals for geodetic applications opens new horizons and poses new challenges. The Center for Orbit Determination in Europe (CODE) is one of the analysis centers of the International GNSS Service (IGS). It has been processing the Galileo data in its multi-GNSS solution since the beginning of the Multi-GNSS Extension (MGEX) project of the IGS.

Solar radiation pressure (SRP) is the largest non-conservative force that impacts satellites in medium Earth orbits. The Galileo satellites, having small weight compared to other GNSS, are particularly sensitive to this effect. Failure to accurately model the SRP-associated accelerations for Galileo may not only result in poorly estimated orbits for these satellites, but also propagate to other solutions via the common least-squares adjustment. The introduction of the extended empirical CODE model (ECOM2) to CODE`s MGEX solution in early 2015 resulted in a significant improvement of the Galileo orbits. The use of the Galileo satellites metadata, which were made public in the course of 2016 and 2017, has further enhanced the quality of the produced solutions. However, they still show significant degradations during eclipse seasons, which are similarly observed in solutions of other analysis centers to different extents. In particular, this is reflected in elevated orbit misclosures at day boundaries, deterioration of satellite clocks and excessive Satellite Laser Ranging (SLR) residuals during these periods. Since the ECOM2 parameters are designed to absorb the effect of solar radiation pressure, they are switched off during eclipses. Hence, there is no empirical force parameter left that can absorb any unmodelled perturbations (e.g., due to thermal radiation (TR)) during an eclipse period.

In this study we refine our orbit model further to address the unmodelled perturbations acting on Galileo satellites, e.g., TR effects while the satellites pass the Earth’s shadow. The presented results include the assessment of the benefits of significantly improved modelling on both IOV and FOC satellites with a focus on eclipse seasons.

The high-latitude ionosphere is characterized by extremely complicated structure. This is mainly related to the transfer of solar wind energy into the ionosphere-magnetosphere system as well as plasma convection pattern in the polar and auroral areas. One of the most prominent high-latitude phenomena are the ionospheric polar patches. These large-scale structures are defined as the enhancements of F-region plasma density, originated from solar ionization on the dayside. The patches are several hundred kilometres in size and their foreground-to-background density ratio ranges from 2 to 10.
The generation and further convection of the patches are currently the objects of intensive multi-instrumental studies, including Global Navigation Satellite Systems (GNSS) measurements. As the recent studies showed, GNSS-based information on patch convection can be derived from Total Electron Content (TEC) mapping as well as time series of geometry-free combination. In this contribution we used the latter approach, which provides epoch-wise information on a relative, slant TEC (STEC) enhancement and ensures the highest temporal resolution. The extracting of patch signatures from geometry-free time series was realized with fitting of 4th order polynomial, corresponding to the background variations of ionosphere. In order to provide a comprehensive view of ionospheric conditions, the proposed algorithm was applied to ~150 permanent stations of worldwide GNSS networks.
The analysis depicts the performance of the algorithm as well as the initial climatological study of the patches during several-month long period of high solar activity. The results proved the efficacy of the network-derived relative STEC values as a patch occurrence indicator and applicability of the current distribution of GNSS stations for this purpose. It was also confirmed that the patches are very frequent phenomena and their occurrence strongly depends on the orientation of Interplanetary Magnetic Field (IMF). The most of structures were detected for southward IMF. In the opposite case the patches are less frequent and weaker. The analysis revealed also a clear relation between dayside TEC and enhancement of these polar structures.

Precise Point Positioning (PPP) enables centimeter accuracy positioning with a single sta-tion. It requires dual-frequency code and phase observables of high quality and expensive GNSS equipment. Because of an economic perspective, single-frequency (SF-) PPP has been receiving increasing interest in recent years. Compared to dual-frequency PPP, the main challenge with SF-PPP is the mitigation of ionospheric effects. In addition to an iono-spheric model, the GRAPHIC (GRoup And PHase Ionosphere Correction) linear combination can be used to overcome the problem of absence of the dual frequencies.
A large data set has been collected from about 75 GURN stations (GNSS Upper Rhine Gra-ben Network) over the whole year 2015. In addition to the global ionospheric maps (GIMs) of the Center for Orbit Determination in Europe (CODE), regional ionospheric maps (RIMs) have been generated by using the Bernese GNSS software. In terms of positioning accuracy of SF-PPP, these two ionospheric models besides the GRAPHIC approach have been evalu-ated in comparison to a network solution.
Our results show that, the residual errors of the ionospheric effect are dominant when using GIMs. The positioning accuracy of the east and height components has distinct spatial and temporal variations. RIMs do not provide any improvement in this context. In contrast, the GRAPHIC approach provides the highest positioning accuracy without any spatial variations related to the ionosphere. Only the east component shows some temporal variations of a few centimeters during the summer time. Anyway, the quality of the code measurements is the main important factor for the GRAPHIC approach. Therefore, the accuracy of GRAPHIC depends on the receiver and antenna types. It may have several centimeter jumps by replac-ing the antenna and/or the receiver on the site. The impact of the Group Delay Variations (GDV) on the SF-PPP has been investigated. Applying code correction values of GDV to the code measurements increases the height accuracy by a factor of two and the east compo-nent accuracy by at least 10%. A 3D positioning accuracy of 4 cm (RMS values over all sta-tions and all days of 2015) can be achieved. For this purpose, GDV as well as phase center offset correction values for the satellite and receiving antennas on the GPS L1 frequency are needed.

In the recent decade, the Global Navigation Satellite System (GNSS) has been increasingly developed. It is rapidly replacing most of the traditional techniques. The GNSS is widely used in many domains: civilian, navigation, surveying, mapping etc. GNSS brings more signals and more satellites (GPS, GLONASS, Galileo, Beidou) that can improve accuracy of receiver position estimation.
The principle of GNSS consists in measuring distances between satellites and users. GNSS receivers use timing signals from at least four satellites and an important number of errors or delays can occur during the signal’s transition to earth. Differential GNSS (DGNSS) is an enhancement to GNSS that was developed to correct these errors and inaccuracies in the GNSS system, allowing for more accurate positioning information.
This paper investigates the position estimation improvement by applying differential GNSS correction. DGNSS correction not only consists of the atmospheric and satellite clock/orbit corrections, but also the correction of the system time offset between the GPS and other constellations[1-2]. In this work, we use the doubles-difference observables to determine the position and the velocity of the receiver. Double-difference can be formed using measurements from two receivers (known and unknown) and two satellites. To combine both systems, the resulting receiver position needs to be expressed in the same coordinate system and time. However, GPS and GLONASS positons are expressed in WGS-84 coordinates and PZ-90.02 coordinates respectively. Furthermore, the time systems used are GPS time system and UTC time system for GLONASS. The present paper proposes a method for data fusion from both systems. To resolve non-linear equations, the least square method is used.
To illustrate the proposed fusion algorithm, the present paper uses the GPS and GLONASS real data from Ensta-Bretagne ship equipped with an acquisition system and deployed in roadstead of Brest on the 30th November 2015. Data are dowloaded in RINEX format 2.11. The ship is considered static with a fixed position. The reference station is BRST in Brest, France. Its RINEX data were downloaded from RGP network on 30 November 2015. For the performance evaluation of the proposed method, root mean square error (RMSE) was used. With GPS data only, the RMS (Root Mean Square) position errors are E_RMS = 2.08 (m), N_RMS = 2.68 (m) and U_RMS = 6.03 (m). Using data fusion, they are reduced to: E_RMS = 0.06 (m), N_RMS = 2.19 (m) and U_RMS = 1.42 (m). Consequently, they are improved by up to 62.28% compared with the use of GPS data only.
Future work can consider combining other signals of satellite systems: Galileo and Beidou in order to enhance the position receiver error correction. Afterwards, the algorithm will be applied for the ship in motion.
[1] Ivan G.Petrovski, “GPS, GLONASS, Galileo, and Beidou for Mobile Device”, CAMBRIDGE University Press.
[2] Scott Gleason, Demoz Gebre-Egziabher, “GNSS Applications and Methods”, Artech House.
The authors would like to note that this abstract falls under the umbrella of topics N03 and N05

The project GREAT, thank to the twin Galileo satellites 201 and 202, injected in an highly eccentric orbits, have performed a new measurement of Relativistic Gravitational Redshift which improved of 5.6 times (α≈2.5*10-5) the previous measurement achieved by GP-A. Our project propose to measure other Satellites General Relativistic effects which could be measured as well: Scharzchild perigee precession and Lense-Thirring gravitomagnetic effect. The measurement of these last really subtle effects need a long stack of data (8-10 years at least). For these reasons G4S, to be fully compliant with is targets, have to be conceived as a long term project. A prerequisite for the success of these measurements is represented by a step forward in the precise orbit determination (POD) of these satellites thanks to the development of more refined models for the subtle disturbing effects related with the non-gravitational perturbations. In particular we plan to develop NGP finite elements modeling and perform a fully exploitation of available SLR tracking data of both the satellites, applying new data analysis strategies and algorithms. Furthermore, these satellites can be the first space facility for the establishment of a pure Relativistic Positioning System (RPS). Bounds on alternative theories of gravity can be settled exploiting the observations of the twin satellites. Finally we have added in the project other objectives in the field of Cosmology and Astrrophysics associated the fully exploitation of the unique features of T& F system onboard GALILEO as well.

Global Navigation Satellite Systems (GNSS) do traditionally not contribute to the scale of the terrestrial reference frame (TRF) since the satellite antenna offsets are not sufficiently known to the scientific community and need to be estimated. In 2016, the European GNSS Agency (GSA) disclosed the satellite antenna calibrations for the Galileo In Orbit Validation (IOV) satellites. In November 2017, also the antenna corrections for the Full Operational Capability (FOC) satellites have been disclosed. With the second disclosure the antenna phase center offsets (PCO) and phase center variations (PCV) for most of the Galileo constellation (the calibrations for the last 8 satellites are not yet released) are now publically available. In addition to Galileo, the Cabinet Office, Government of Japan (CAO) has also released the satellite antenna calibrations for QZSS.

For the receiver antennas the situation is different. Most of the receiver antennas in the IGS network have type-mean calibrations based on dual frequency robot calibration. Since these calibrations include only GPS and GLONASS, no patterns for the second Galileo frequencies are available at the moment (the assumption that E1 is similar to L1 seems reasonable). Chamber calibrations from the University of Bonn include all frequencies covering a wide range of antennas used within the IGS/MGEX. After an IGS call for antenna chamber calibrations, many institutions provided their calibrations to this study.

We will present a study which aims to assess the potential of chamber calibrations within a Multi-GNSS (MGEX) solution (namely Galileo) for the determination of a GNSS scale. A scale contribution from GNSS would allow future International TRF (ITRF) solutions to not only depend on VLBI and SLR for the scale determination but also to benefit from GNSS as a third technique.