Search

An alternative approach to detect solar flares and quantify the associated extreme ultraviolet (EUV) solar flux rate was introduced in this journal by the authors: Global Navigation Satellite Systems Solar FLAre Indicator (GSFLAI) was founded on the dependence of the sudden electron content increase of the Earth ionosphere versus the angle regarding the flare source, the Sun, given by a simple but accurate first‐principles‐based model. Such overionization is directly measured from the dual‐frequency phase measurements gathered from hundreds of worldwide permanent receivers of the Global Navigation Satellite Systems, GNSS (like the Global Positioning System GPS), working many of them in real time. In this work we generalize GSFLAI for the very challenging scenario of stellar superflares, with a much weaker expected geoeffectiveness on the Earth ionosphere, making it difficult to distinguish its potential footprint regarding conventional ionospheric variability sources. Indeed, we will show that, unlike GSFLAI for solar flares, the new algorithm presented here (Blind GNSS search of Extraterrestrial EUV Sources [BGEES]) is able to detect EUV flares without the previous knowledge of the position of the source, which is also simultaneously estimated, providing an additional quality check of the detection. It will be first assessed with several case studies of solar flares of different intensities analyzed previously with GSFLAI. Finally, by focusing on the night hemisphere to avoid the Sun's larger effect on the ionosphere, the detection and location with BGEES of two recent stellar superflares, Proxima Centauri (18 March 2016, 08:32UT) and NGTS J121939.5‐355557 (1 February 2016, 04:00UT), are presented, strongly suggesting the extension and applicability of the new technique, also in real time. Key Points: The simultaneous determination of stellar EUV flares in time and location with the existing GNSS infrastructure is presentedIt is based on the modeling of the Earth ionosphere electron content increase, from dual‐frequency GNSS data, due to the stellar flareThe new technique is assessed versus several solar flares of different intensities and two stellar superflares previously studied in detail [ABSTRACT FROM AUTHOR]

This paper presents a review on the PECASUS service, which provides advisories on enhanced space weather activity for civil aviation. The advisories are tailored according to the Standards and Recommended Practices of the International Civil Aviation Organization (ICAO). Advisories are disseminated in three impact areas: radiation levels at flight altitudes, GNSS-based navigation and positioning, and HF communication. The review, which is based on the experiences of the authors from two years of running pilot ICAO services, describes empirical models behind PECASUS products and lists ground- and space-based sensors, providing inputs for the models and 24/7 manual monitoring activities. As a concrete example of PECASUS performance, its products for a post-storm ionospheric F2-layer depression event are analyzed in more detail. As PECASUS models are particularly tailored to describe F2-layer thinning, they reproduce observations more accurately than the International Reference Ionosphere model (IRI(STORM)), but, on the other hand, it is recognized that the service performance is much affected by the coverage of its input data. Therefore, more efforts will be directed toward systematic measuring of the availability, timeliness and quality of the data provision in the next steps of the service development.

Global satellite navigation systems (GNSS) has firmly entered not only in the daily life of society, but also widely used in various fields of scientific application. The possibility of conducting continuous observations at permanent GNSS stations, which do not depend on weather conditions, allowed to accumulate long periods of observations. All this led to the acquisition of precision time coordinate with accuracy of several millimeters. One of the first steps in the study of the local level of the crustal deformation is the estimation of the values of the displacement velocities of the GNSS stations. One of the simplest and most widespread ways of representing the horizontal movements of the earth's surface occurring within the region under study is the acquisition of a velocity field. GNSS data analysis center of GAO NASU received estimates of velocity vectors for 233 GNSS stations (in coordinate system IGb08), 202 of which are located in Ukraine. The maximum assessment period was from December 7, 1997 – January 28, 2017, or 6,993 days (approximately 20 years). The rate estimation is based on GNSS observations of state, academic, university and commercial networks of Ukraine. The velocity vectors were obtained using the Bernese GNSS Software Ver. 5.2 (ADDNEQ2 and FODITS software modules were used) recommended by the GNSS Data Analysis Centers, in particular by the EUREF European Center for research of this type. The obtained estimates of the velocity vectors fully coincide with the movement of the Eurasian lithospheric plate. For further use in studies on the deformation of the Earth's crust, each GNSS station should be thoroughly tested for possible effects (caused by the operation of the apparatus, human factor, etc.), as well as to satisfy the minimum observation period of three years.

Most developing countries like Ghana are yet to adopt the geocentric datum for its surveying and mapping purposes. It is well known and documented that non-geocentric datums based on its establishment have more distortions in height compared with satellite datums. Most authors have argued that combining such height with horizontal positions (latitude and longitude) in the transformation process could introduce unwanted distortions to the network. This is because the local geodetic height in most cases is assumed to be determined to a lower accuracy compared with the horizontal positions. In the light of this, a transformation model was proposed by Featherstone and Vaníček (1999) which avoids the use of height in both global and local datums in coordinate transformation. It was confirmed that adopting such a method reduces the effect of distortions caused by geodetic height on the transformation parameters estimated. Therefore, this paper applied Featherstone and Vaníček (FV) model for the first time to a set of common points coordinates in Ghana geodetic reference network. The FV model was used to transform coordinates from global datum (WGS84) to local datum (Accra datum). The results obtained based on the Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) in both Eastings and Northings were satisfactory. Thus, a RMSE value of 0.66 m and 0.96 m were obtained for the Eastings and Northings while 0.76 m and 0.73 m were the MAE values achieved. Also, the FV model attained a transformation accuracy of 0.49 m. Hence, this study will serve as a preliminary investigation in avoiding the use of height in coordinate transformation within Ghana’s geodetic reference network.

The limitations of Kalman filter (KF) have motivated researchers to consider alternative methods of integrating inertial navigation systems (INS) and global navigation satellite systems (GNSS), predominantly based on artificial intelligence (AI). Over the past two decades, a great number of research gained in order to validate the possibility of using AI methods in the field of integrated navigation systems. Different approaches have been proposed for combining AI modules with the other parts of the INS/GNSS system. The article suggests a new classification of the resulting schemes based on the functionality of AI modules in the INS/GNSS system. The paper also provides a brief explanation of each scheme with its advantages and disadvantages. Some aspects that need to be considered in future research in this field are also highlighted. [ABSTRACT FROM AUTHOR]

Errors induced by the ionosphere on global navigation satellite systems (GNSS) signal propagation significantly affect the positioning calculation done by ground receivers. These ionospheric errors may end up reaching tens of meters in the final positioning calculation. In this study, the ionospheric range error (IRE) was monitored over the local ionosphere of BAHR, Bahrain (26.209N, 50.608E) during the period of the 23rd solar cycle. IRE values were obtained through observation data derived from RINEX files and compared with NeQuick 2 (NQ2) model calculations. It was found that, for the region of study, NQ2 overestimated the total electron content (TEC) values as compared to observation data, resulting in higher IRE values of up to 12 m. However, IRE derived using GNSS observations and NQ2 follow similar trends over the course of the solar cycle. IRE values were also compared to the smoothed sunspot number (SSN) and F 10.7 indexes which resulted in significant correlation between the seasonal calculation of IRE and solar activity. Throughout the 23rd solar cycle, the highest IRE values were found during the equinoxes and the lowest during solstices. The largest IRE value was observed in the vernal equinox of 2000 (19.13 m), while the lowest IRE value was observed in the winter solstice of 1998 (0.276 m). [ABSTRACT FROM AUTHOR]

• Multipath interference mitigation in GNSS receivers is formulated as a joint state and time-varying parameter estimation problem. • The proposed joint state and time-varying parameter estimation problem in the context of multipath mitigation is conducted using an expectation-maximization (EM) algorithm. • The convergence of the proposed EM-based multipath mitigation algorithm is analyzed. • The proposed localization algorithm shows a good robustness in multipath environments. In multipath (MP) environments, the received signals depend on several factors related to the global navigation satellite systems (GNSS) receiver environment and motion. Thus it is difficult to use a specific propagation model to accurately capture the dynamics of the MP signal when the GNSS receiver is moving in urban canyons. This paper formulates the problem of MP interference mitigation in the GNSS receiver as a joint state (containing the direct signal parameters) and time-varying model parameter (containing the MP signal parameters) estimation. Accordingly, we propose to exploit the EM algorithm for achieving the joint state and time-varying parameter estimation in the context of MP interference mitigation in GNSS receivers. More precisely, the proposed EM-based MP mitigation approach is decomposed into two iterative steps: (a) the posterior pdf of the direct signal parameters and the expected log-likelihood function necessary in the expectation step of the EM algorithm are approximated by using an appropriate particle filter; (b) the maximum likelihood solution for MP signal parameters is then obtained using Newton's method in the maximization step. The convergence of the proposed approach is analyzed based on the existing convergence theorem associated with the EM algorithm. Finally, a comprehensive simulation study is conducted to compare the performance of the proposed EM-based MP mitigation approach with other state-of-the-art MP mitigation approaches in static and realistic scenarios. [ABSTRACT FROM AUTHOR]

Time series of integrated water-vapor (IWV) content for 2015–2017 at eight paired GNSS stations and solar photometry data from the AERONET network in Europe have been compared. The distance between station pairs was no more than 20 km. The average and standard deviations of discrepancies have been shown to vary seasonally. The GNSS–photometer bias in winter was from –0.61 to 0.34 mm. The IWV content in summer is overestimated by the GNSS relative to photometers by 0.52 to 2.26 mm. The standard deviation is from 1.31 to 1.64 mm with a maximum in summer and decreases to 0.49–0.86 mm in winter, which is 5–6% of IWV. [ABSTRACT FROM AUTHOR]

This paper presents the results of observations of atmospheric and ionospheric parameters performed during a meteorological storm that occurred over the Kaliningrad region in December 2010. The analysis of the observations shows that the ionospheric inhomogeneities at mid-latitudes arising during the periods of meteorological disturbances are manifested as a decrease in the total electron content and the critical frequency of the F2 layer by 33 and 15%, respectively. It is shown that meteorological disturbances of the mid-latitude atmosphere can be manifested in the ionosphere and in the near-equatorial latitudes as increased TEC values. This indicates the complex nature of physical processes that determine the relationship between dynamics in the lower and upper atmosphere. [ABSTRACT FROM AUTHOR]

Highlights • Real time assessment of IEEE 1588 with multi-protocol traffic interactions. • Combined GNSS and IEEE 1588 systems offer a more reliable timing performance. • Manufactures have vendor-specific interpretations of IEEE 1588 messages. • IEEE 1588 satisfies the ±1 μs accuracy requirement in transmission substations. • Use capture card and impairment simulator to identify performance boundary. Abstract Accurate timestamping with 1 µs precision is required by power system monitoring and control equipment, including: Phase Measurement Units (PMUs) for real-time measurement and control; travelling wave detectors for fault location, protection and control; and sample value measurement techniques associated with the IEC 61850 process bus. The conventional way of achieving this is to transmit 1-PPS or IRIG-B timing signals using dedicated cables but such an approach is expensive and difficult to update as secondary control systems evolve. IEEE 1588 precision time protocol (PTP) allows the transmission of time information with sub-microsecond accuracy in an Ethernet network. However, a comprehensive study is required to enhance the confidence of the power industry in using PTP in present and future IEC 61850 based substations. This paper delivers a design and experimental validation of the real-time time synchronisation characteristics achievable with IEEE 1588. Several factors which can potentially affect the synchronisation accuracy in delivering a time reference from the master clocks to the end devices during both steady-state and transient changes were investigated. The objective is to increase the understanding of the real-time performance of a complete IEEE 1588 timing system applied in transmission substations, and identify the limitations of commercially-available devices. [ABSTRACT FROM AUTHOR]

Abstract Dynamical evolution of space debris in the vicinity of orbits of the global navigation satellite systems: GLONASS, GPS, BeiDou, and Galileo was studied for a time span of 240 years. Time intervals space debris objects reach the regions of motion of navigation satellites were estimated. Initial orbits of the objects were chosen in the GNSS orbit regions as well as 450–1100 km above with respect to nominal semi-major axes of the navigation orbits. The results depend significantly on the orbital plane position. The objects pass through the GNSS region due to long period oscillations of eccentricities and inclinations of orbits, which are caused by dependency of inclination on luni-solar resonances and radiation pressure. [ABSTRACT FROM AUTHOR]

Today rapid-static GPS is an alternative surveying technique among other fundamental GPS surveying methods such as real-time kinematic and static GPS. It usually finds application areas in engineering surveying and monitoring of ground deformation for example landslides. Web-based GPS software such as OPUS-RS which was developed by the National Geodetic Survey (NGS) promoted further the use of the technique. NGS also provides its users the obtainable accuracy of the OPUS-RS derived solutions. Minimum 15 min of GPS data is recommended for rapid-static positioning and the accuracy is given accordingly. In this study, we go beyond the typically recommended 15 min observations and examine the accuracy variation of rapid-static OPUS positioning solutions over 8–118 min interval. Seven Continuously Operating Reference Stations from the US are selected, and their data are segmented into the above-mentioned shorter sessions. Statistical analyses of the CORS stations revealed that solutions from 15 min or shorter sessions contain outliers, and this degrades the efficiency of the technique. By extending the typical 15 min observation length up to 60 min perfectly eliminates the outliers, and the accuracy on the average is improved by about 5–20 mm for horizontal and about 25 mm for vertical components. [ABSTRACT FROM AUTHOR]

The precise point positioning (PPP) is a Global Navigation Satellite System (GNSS) computation technique that performs precise positioning using a single receiver. This is the main advantage over the traditional differential positioning for geodesy and geomatics which requires, at least, two receivers to get a precise position or a single receiver connected to a network of reference stations. The main goal of this work was to study the real-time PPP technique for deformation and landslides monitoring. A custom designed device was used for the simulation of landslides, and several test campaigns were performed at field. A control unit was designed based on open-source software and Python libraries implemented in this research. The conclusion of the study shows that real-time PPP allows solutions for deformation monitoring with mean offsets of 2 cm in north, east and up components, and standard deviations of 2 cm. It demonstrates the reliability of real-time PPP monitoring systems to detect deformations up to 5 cm of magnitude when the double constellation (GPS+GLONASS) was used. Finally, an improvement in the results with the recovery of fixed ambiguities in the PPP algorithms is outlined.

The electronic receivers of global navigation satellite systems (GNSSs) are implemented in various handheld electronic devices such as laptops, smartphones, and smartwatches; therefore, their dimensions are of critical importance. Achieving a GNSS terminal of a small size is difficult due to its relatively low operational frequency (L-band), which is equivalent to a wavelength of approximately 24 cm. As an efficient half-wavelength antenna is too large for compact devices, in this paper, an electrically small antenna (ESA) for GNSS terminals is presented. The antenna was miniaturized by using a dielectric block with relatively high permittivity, making some parts virtual, and optimizing its geometry. The operational frequency of the ESA is tunable by means of metallic rods of variable heights inserted into a cylindrical cavity drilled inside the dielectric block. The results confirm the feasibility of the concept and the usability of the ESA for compact GNSS terminals.

The ionosphere is one of the main error sources in positioning and navigation; thus, information about the ionosphere is mandatory for precise modern Global Navigation Satellite System (GNSS) applications. The International GNSS Service (IGS) and its Ionosphere Associated Analysis Centers (IAAC) routinely provide ionospheric information in terms of global ionosphere maps (final GIM). Typically, these products are modeled using series expansion in terms of spherical harmonics (SHs) with a maximum degree of n=15 and are based on post processed observations from Global Navigation Satellite Systems (GNSS), as well as final satellite orbits. However, precise applications such as autonomous driving or precision agriculture require real-time (RT) information about the ionospheric electron content with high spectral and spatial resolution. Ionospheric RT-GIMs are disseminated via Ntrip protocol using the SSR VTEC message of the RTCM. This message can be streamed in RT, but it is limited for the dissemination of coefficients of SHs of lower degrees only. It allows the dissemination of SH coefficients up to a degree of n=16. This suits to most the SH models of the IAACs, but higher spectral degrees or models in terms of B-spline basis functions, voxels, splines and many more cannot be considered. In addition to the SHs, several alternative approaches, e.g., B-splines or Voxels, have proven to be appropriate basis functions for modeling the ionosphere with an enhanced resolution. Providing them using the SSR VTEC message requires a transfer to SHs. In this context, the following questions are discussed based on data of a B-spline model with high spectral resolution; (1) How can the B-spline model be transformed to SHs in order to fit to the RTCM requirements and (2) what is the loss of detail when the B-spline model is converted to SHs of degree of n=16? Furthermore, we discuss (3) what is the maximum necessary SH degree n to convert the given B-spline model and (4) how can the transformation be performed to make it applicable for real-time applications? For a final assessment, we perform both, the dSTEC analysis and a single-frequency positioning in kinematic mode, using the transformed GIMs for correcting the ionospheric delay. The assessment shows that the converted GIMs with degrees n≥30 coincide with the original B-spline model and improve the positioning accuracy significantly.

The ionosphere is one of the largest error sources in GNSS (Global Navigation Satellite Systems) applications and can cause up to several meters of error in positioning. Especially for single-frequency users, who cannot correct the ionospheric delay, the information about the state of the ionosphere is mandatory. Dual- and multi-frequency GNSS users, on the other hand, can correct the ionospheric effect on their observations by linear combination. However, real-time applications such as autonomous driving or precision farming, require external high accuracy corrections for fast convergence. Mostly, this external information is given in terms of grids or coefficients of the vertical total electron content (VTEC). Globally distributed GNSS stations of different networks, such as the network of the International GNSS Services (IGS), provide a large number of multi-frequency observations which can be used to determine the state of the ionosphere. These data are used to generate Global Ionosphere Maps (GIM). Due to the inhomogeneous global distribution of GNSS real-time stations and especially due to the large data gaps over oceanic areas, the global VTEC models are usually limited in their spatial and spectral resolution. Most of the GIMs are mathematically based on globally defined radial basis functions, i.e., spherical harmonics (SH), with a maximum degree of 15 and provided with a spatial resolution of 2.5 ° × 5 ° in latitude and longitude, respectively. Regional GNSS networks, however, offer dense clusters of observations, which can be used to generate regional VTEC solutions with a higher spectral resolution. In this study, we introduce a two-step model (TSM) comprising a global model as the first step and a regional model as the second step. We apply polynomial and trigonometric B-spline functions to represent the global VTEC. Polynomial B-splines are used for modelling the finer structures of VTEC within selected regions, i.e., the densification areas. The TSM provides both, a global and a regional VTEC map at the same time. In order to study the performance, we apply the developed approach to hourly data of the global IGS network as well as the EUREF network of the European region for St. Patrick storm in March 2015. For the assessment of the generated maps, we use the dSTEC analysis and compare both maps with different global and regional products from the IGS Ionosphere Associated Analysis Centers, e.g., the global product from CODE (Berne, Switzerland) and from UPC (Barcelona, Spain), as well as the regional maps from ROB (Brussels, Belgium). The assessment shows a significant improvement of the regional VTEC representation in the form of the generated TSM maps. Among all other products used for comparison, the developed regional one is of the highest accuracy within the selected time span. Since the numerical tests are performed using hourly data with a latency of one to two hours, the presented procedure is seen as an intermediate step for the generation of high precision regional real-time corrections for modern applications.

Advances in global navigation satellite system (GNSS) technology have resulted in smaller and more accurate GNSS receivers, which have become increasingly suitable for calculating instantaneous performance parameters during sports competitions, for example by providing the difference in time between athletes at any location along a course. This study investigated the accuracy of three commercially available GNSS receivers directed at the sports market and evaluated their applicability for time analysis in endurance racing sports. The receivers evaluated were a 1 Hz wrist-worn standalone receiver (Garmin Forerunner 920XT, Gar-920XT), a 10 Hz standalone receiver (Catapult Optimeye S5, Cat-S5), and a 10 Hz differential receiver (ZXY-Go). They were validated against a geodetic, multi-frequency receiver providing differential position solutions (accuracy < 5 cm). Six volunteers skied four laps on a 3.05 km track prepared for cross-country skiing, with all four GNSS receivers measuring simultaneously. Deviations in position (horizontal plane, vertical, direction of travel) and speed (horizontal plane and direction of travel) were calculated. In addition, the positions of all receivers were mapped onto a mapping trajectory along the ski track, and a time analysis of all 276 possible pairs of laps was performed. Specifically, the time difference between any two skiers for each integer meter along the track was calculated. ZXY-Go, CAT-S5, and GAR-920XT had horizontal plane position errors of 2.09, 1.04, and 5.29 m (third quartile, Q3), and vertical precision 2.71, 3.89, and 13.35 m (interquartile range, IQR), respectively. The precision in the horizontal plane speed was 0.038, 0.072, and 0.66 m s-1 (IQR) and the time analysis precision was 0.30, 0.13, and 0.68 s (IQR) for ZXY-Go, Cat-S5, and Gar-920XT, respectively. However, the error was inversely related to skiing speed, implying that for the low speeds typically attained during uphill skiing, substantially larger errors can occur. Specifically, at 2.0 m s-1 the Q3 was 0.96, 0.36, and 1.90 s for ZXY-Go, Cat-S5, and Gar-920XT, respectively. In summary, the differential (ZXY-Go) and 10 Hz standalone (Cat-S5) receivers performed substantially better than the wrist-worn receiver (Gar-920XT) in terms of horizontal position and horizontal speed calculations. However, all receivers produced sub-second accuracy in the time analysis, except at very low skiing speeds.

The tightly coupled integration with serial measurement processing of the pseudo ranges and carrier Doppler measurements is investigated. The spatial information of inertial navigation systems is used for determination satellite attitude relative to directional diagram and for signal search stoppage at the time of the flight maneuver.

Currently four global satellite navigation systems are under modernization and development: The US American GPS III, the Russian GLONASS, the European Galileo and Chinese BeiDou systems. In the paper the interdisciplinary contributions of different scientific areas to GNSS are assessed. It is outlined that GNSS is not only a technical system but also a basic element of mobile computing high-tech market. At the same time a GNSS has the role of a force enabler in security related applications. Technology, market and security policies are interdependent and are sometimes in a relationship of tension. The goal of the paper is to describe the overall systemics of GNSS from a holistic point of view. The paper also addresses the human factor side of GNSS. The requirements on human resources in GNSS are at least two-fold: On the one hand very specialized engineers are needed; on the other hand the generalists are necessary who are able to understand the system aspects. Decision makers in institutions and industry need special knowledge in technologies, economics and political strategies. Is the current university system able to educate and prepare such generalists? Are specialized master courses for GNSS needed? Are external training courses necessary?

Advances in global navigation satellite system (GNSS) technology have resulted in smaller and more accurate GNSS receivers, which have become increasingly suitable for calculating instantaneous performance parameters during sports competitions, for example by providing the difference in time between athletes at any location along a course. This study investigated the accuracy of three commercially available GNSS receivers directed at the sports market and evaluated their applicability for time analysis in endurance racing sports. The receivers evaluated were a 1 Hz wrist-worn standalone receiver (Garmin Forerunner 920XT, Gar-920XT), a 10 Hz standalone receiver (Catapult Optimeye S5, Cat-S5), and a 10 Hz differential receiver (ZXY-Go). They were validated against a geodetic, multi-frequency receiver providing differential position solutions (accuracy < 5 cm). Six volunteers skied four laps on a 3.05 km track prepared for cross-country skiing, with all four GNSS receivers measuring simultaneously. Deviations in position (horizontal plane, vertical, direction of travel) and speed (horizontal plane and direction of travel) were calculated. In addition, the positions of all receivers were mapped onto a mapping trajectory along the ski track, and a time analysis of all 276 possible pairs of laps was performed. Specifically, the time difference between any two skiers for each integer meter along the track was calculated. ZXY-Go, CAT-S5, and GAR-920XT had horizontal plane position errors of 2.09, 1.04, and 5.29 m (third quartile, Q3), and vertical precision 2.71, 3.89, and 13.35 m (interquartile range, IQR), respectively. The precision in the horizontal plane speed was 0.038, 0.072, and 0.66 m s-1 (IQR) and the time analysis precision was 0.30, 0.13, and 0.68 s (IQR) for ZXY-Go, Cat-S5, and Gar-920XT, respectively. However, the error was inversely related to skiing speed, implying that for the low speeds typically attained during uphill skiing, substantially larger errors can occur. Specifically, at 2.0 m s-1 the Q3 was 0.96, 0.36, and 1.90 s for ZXY-Go, Cat-S5, and Gar-920XT, respectively. In summary, the differential (ZXY-Go) and 10 Hz standalone (Cat-S5) receivers performed substantially better than the wrist-worn receiver (Gar-920XT) in terms of horizontal position and horizontal speed calculations. However, all receivers produced sub-second accuracy in the time analysis, except at very low skiing speeds. [ABSTRACT FROM AUTHOR]

Signals from Global Navigation Satellite Systems are the primary source for Position, Navigation and Time (PNT) information onboard any vessel today. As these signals are prone to interference, a maritime backup system is needed to provide reliable PNT data, R(anging)-Mode is such a system. It utilizes existing maritime radio beacons or base stations of the Automatic Identification System (AIS) by adding ranging components to the legacy signals. The first modified radio beacons transmit medium frequency (MF) R-Mode signals in northern Germany. This paper has described the current state of the authors' research and development activities at the receiver level for MF R-Mode signals. The receiver platform has been introduced, which was based on off-theshelf components and the implemented algorithms for distance estimation have been explained. Furthermore, the results of the first ranging measurements have been presented, which have shown the general suitability of the R-Mode technology as a source for maritime positioning and timing data. [ABSTRACT FROM AUTHOR]

Localization algorithms based on global navigation satellite systems (GNSS) play an important role in automotive positioning. Due to the advent of autonomously driving cars, their importance is expected to grow even further in the next years. Simultaneously, the performance requirements for these localization algorithms will increase because they are no longer used exclusively for navigation, but also for control of the vehicle’s movement. These requirements cannot be met with GNSS alone. Instead, algorithms for sensor data fusion are needed. While the combination of GNSS receivers with inertial measurements units (IMUs) is a common approach, it is traditionally executed in a single-frequency/single-constellation architecture, usually with the Global Positioning System’s (GPS) L1 C/A signal. With the advent of new GNSS constellations and civil signals on multiple frequencies, GNSS/IMU integration algorithm performance can be improved by utilizing these new data sources. To achieve this, we upgraded a tightly coupled GNSS/IMU integration algorithm to process measurements from GPS (L1 C/A, L2C, L5) and Galileo (E1, E5a, E5b). After investigating various combination strategies, we chose to preferably work with ionosphere-free combinations of L5-L1 C/A and E5a-E1 pseudo-ranges. L2C-L1 C/A and E5b-E1 combinations as well as single-frequency pseudo-ranges on L1 and E1 serve as backup when no L5/E5a measurements are available. To be able to process these six types of pseudo-range observations simultaneously, the differential code biases (DCBs) of the employed receiver need to be calibrated. Time-differenced carrier-phase measurements on L1 and E1 provide the algorithm with pseudo-range-rate observations. To provide additional aiding, information about the vehicle’s velocity obtained by an odometry model fed with angular velocities from all four wheels as well as the steering wheel angle is incorporated into the algorithm. To evaluate the performance improvement provided by these new data sources, two sets of measurement data are collected and the resulting navigation solutions are compared to a higher-grade reference system, consisting of a geodetic GNSS receiver for real-time kinematic positioning (RTK) and a navigation grade IMU. The multi-frequency/multi-constellation algorithm with odometry aiding achieves a 3-D root mean square (RMS) position error of 3.6 m/2.1m in these data sets, compared to 5.2m/2.9m for the single-frequency GPS algorithm without odometry aiding. Odometry is most beneficial to positioning accuracy when GNSS measurement quality is poor. This is demonstrated in data set 1, resulting in a reduction of the horizontal position error’s 95% quantile from 6.2m without odometry aiding to 4.2m with odometry aiding. [ABSTRACT FROM AUTHOR]

An error in calculating the tropospheric delay of satellite navigation signals is estimated for different atmospheric phenomena. As atmospheric phenomena, different precipitation types (hydrometeors) and electrical phenomena (thunderstorms and summer lightning) are considered. The tropospheric delay is calculated for the Saastamoinen and Hopfield models with the vertical profiles of the atmospheric meteorological parameters obtained by aerological sounding. The error of the given methods is determined by a comparison of the calculated and true values of the zenith tropospheric delays. The influence of the atmospheric phenomena on the error value is analyzed. [ABSTRACT FROM AUTHOR]

In the context of the International GNSS Service (IGS), several IGS Ionosphere Associated Analysis Centers have developed different techniques to provide global ionospheric maps (GIMs) of vertical total electron content (VTEC) since 1998. In this paper we present a comparison of the performances of all the GIMs created in the frame of IGS. Indeed we compare the classical ones (for the ionospheric analysis centers CODE, ESA/ESOC, JPL and UPC) with the new ones (NRCAN, CAS, WHU). To assess the quality of them in fair and completely independent ways, two assessment methods are used: a direct comparison to altimeter data (VTEC-altimeter) and to the difference of slant total electron content (STEC) observed in independent ground reference stations (dSTEC-GPS). The main conclusion of this study, performed during one solar cycle, is the consistency of the results between so many different GIM techniques and implementations. [ABSTRACT FROM AUTHOR]

Planar-controlled reception pattern antenna (CRPA) arrays suffer from low null resolution at low elevation angles, which results in a diminished angular space available for reception. The null resolution becomes even worse as the array aperture size is shrunk in modern compact CRPAs. Nonplanar arrays have been used to address this issue, but they are high profile and bulky. A novel planar solution, specifically suited for compact arrays, is proposed in this communication. We show that by utilizing concentric dual-mode TM11–TM21 circular microstrip antenna elements in an array, an angular availability similar to a spherical array can be achieved. This is demonstrated by studying the array nulling performance in many Monte Carlo trials with randomly polarized interferers, where the adapted array patterns are computed using a simple null-steering algorithm. [ABSTRACT FROM PUBLISHER]

External forces, such as ground reaction force or air drag acting on athletes' bodies in sports, determine the sport-specific demands on athletes' physical fitness. In order to establish appropriate physical conditioning regimes, which adequately prepare athletes for the loads and physical demands occurring in their sports and help reduce the risk of injury, sport-and/or discipline-specific knowledge of the external forces is needed. However, due to methodological shortcomings in biomechanical research, data comprehensively describing the external forces that occur in alpine super-G (SG) and downhill (DH) are so far lacking. Therefore, this study applied new and accurate wearable sensor-based technology to determine the external forces acting on skiers during World Cup (WC) alpine skiing competitions in the disciplines of SG and DH and to compare these with those occurring in giant slalom (GS), for which previous research knowledge exists. External forceswere determined using WC forerunners carrying a differential global navigation satellite system (dGNSS). Combining the dGNSS data with a digital terrain model of the snow surface and an air drag model, the magnitudes of ground reaction forces were computed. It was found that the applied methodology may not only be used to track physical demands and loads on athletes, but also to simultaneously investigate safety aspects, such as the effectiveness of speed control through increased air drag and ski-snow friction forces in the respective disciplines. Therefore, the component of the ground reaction force in the direction of travel (ski-snow friction) and air drag force were computed. This study showed that (1) the validity of high-end dGNSS systems allows meaningful investigations such as characterization of physical demands and effectiveness of safety measures in highly dynamic sports; (2) physical demands were substantially different between GS, SG, and DH; and (3) safety-related reduction of skiing speed might be most effectively achieved by increasing the ski-snow friction force in GS and SG. For DH an increase in the ski-snow friction force might be equally as effective as an increase in air drag force. [ABSTRACT FROM AUTHOR]

Ionospheric scintillation can seriously impair the Global Navigation Satellite Systems (GNSS) receiver signal tracking performance, thus affecting the required levels of availability, accuracy and integrity of positioning that supports modern day GNSS based applications. We present results from the research work carried out under the Horizon 2020 European Commission (EC) funded Ionospheric Prediction Service (IPS) project. The statistical models developed to estimate the standard deviation of the receiver Phase Locked Loop (PLL) tracking jitter on the Global Positioning System (GPS) L1 frequency as a function of scintillation levels are presented. The models were developed following the statistical approach of generalized linear modelling on data recorded by networks in operation at high and low latitudes during the years of 2012–2015. The developed models were validated using data from different stations over varying latitudes, which yielded promising results. In the case of mid-latitudes, as the occurrence of strong scintillation is absent, an attempt to develop a dedicated model proved fruitless and, therefore, the models developed for the high and low latitudes were tested for two mid-latitude stations. The developed statistical models can be used to generate receiver tracking jitter maps over a region, providing users with the expected tracking conditions. The approach followed for the development of these models for the GPS L1 frequency can be used as a blueprint for the development of similar models for other GNSS frequencies, which will be the subject of follow on research.

This paper presents geometrically and physically defined height systems, along with their evaluation by the means of Global Navigation Satellite Systems (GNSS) and Global Geopotential Models (GGM). The paper defines ellipsoid heights as an instance of geometrically defined heights; with physically defined heights being represented by definitions of orthometric and normal heights. Methods of normal heights calculation by the means of ellipsoid heights are presented in detail, as determined using the GNSS and height anomalies calculated from the GGM application. Apart from the above, numerical part of the paper evaluates normal height values and compares them to their conditionally accurate values at 1073 points with relatively uniform distribution over the entire territory of Serbia. Conditionally accurate values had been determined by the means of classical geodetic terrestrial methods. Under the procedure of evaluating normal height values, GGM - GGM05C was used, as created in 2016 by the Center for Space Research, University of Texas at Austin. In order to evaluate the quality of applying the model above, data on normal heights evaluation were also presented, using the GGM EGM96, created in 1996 by the National Imagery and Mapping Agency (NIMA), Goddard Space Flight Center (GSFC - NASA) and Ohio State University, presently being the most commonly used model. The comparison above indicates that application of the GGM05C model provides 50 % greater quality of normal heights evaluations against the ones obtained using the EGM96 model. [Projekat Ministarstva nauke Republike Srbije, br. TR 36020]

We report two comments affecting the paper “Curto JJ, Juan JM & Timoté CC, 2019. Confirming geomagnetic Sfe by means of a solar flare detector based on GNSS. J Space Weather Space Clim 9: A42. https://doi.org/10.1051/swsc/2019040”: The first comment is the reporting of two mistakes which distorts the central model used for the measurement and detection of solar flares with GNSS, that might affect as well the most part of results and discussions contained in the paper. And the second comment is the clarification about the authors’ claim of presenting the first work of using the electron content enhancement estimation at the subsolar point for characterizing solar flares with GNSS data, which is not accurate due to the existence of such previous definition and usage.

MEMS Inertial Measurement Units are available at low cost and can replace expensive units in mobile mapping platforms which need direct georeferencing. This is done through the integration with GNSS measurements in order to achieve a continuous positioning solution and to obtain orientation angles. This paper presents the results of the assessment of the accuracy of a system that integrates GNSS and a MEMS IMU in a terrestrial platform. We describe the methodology used and the tests realized where the accuracy of the positions and orientation parameters were assessed using an independent photogrammetric technique employing cameras that integrate the mobile mapping system developed by the authors. Results for the accuracy of attitude angles and coordinates show that accuracies better than a decimeter in positions, and under a degree in angles, can be achieved even considering that the terrestrial platform is operating in less than favorable environments.

Typhoons can be serious natural disasters for the sustainability and development of society. The development of a typhoon usually involves a pre-existing weather disturbance, warm tropical oceans, and a large amount of moisture. This implies that a large variation in the atmospheric water vapor over the path of a typhoon can be used to study the characteristics of the typhoon. This is the reason that the variation in precipitable water vapor (PWV) is often used to capture the signature of a typhoon in meteorology. This study investigates the usability of real-time PWV retrieved from global navigation satellite systems (GNSS) for typhoons’ characterizations, and especially, the following aspects were investigated: (1) The correlation between PWV and atmospheric parameters including pressure, temperature, precipitation, and wind speed; (2) water vapor transportation during a typhoon period; and (3) the correlation between the movement of a typhoon and the transportation of water vapor. The case study selected for this research was Super Typhoon Mangkhut that occurred in mid-September 2018 in Hong Kong. The PWV time series were obtained from a conversion of GNSS-derived zenith total delays (ZTDs) using observations at 10 stations selected from the Hong Kong GNSS continuously operating reference stations (CORS) network, which are also located along the path of the typhoon. The Bernese GNSS Software (ver. 5.2) was used to obtain the ZTDs; and the root mean square (RMS) of the differences between the GNSS-ZTDs and International GNSS Service post-processed ZTDs time series was less than 8 mm. The RMS of the differences between the GNSS-PWVs (i.e., the ZTDs converted PWVs) and radiosonde-derived PWVs (RS-PWVs) time series was less than 2 mm. The changes in PWV reflect the variation in wind speed during the typhoon period to a certain degree, and their correlation coefficient was 0.76, meaning a significant positive correlation. In addition, a new approach was proposed to estimate the direction and speed of a typhoon’s movement using the time difference of PWV arrival at different sites. The direction and speed estimated agreed well with the ones published by the China Meteorological Administration. These results suggest that GNSS-derived PWV has a great potential for the monitoring and even prediction of typhoon events, especially for near real-time warnings.