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As low‐cost global navigation satellite systems receiver and antenna become increasingly prevalent for water vapour monitoring, precise millimetre‐level characterisation of instrument biases is crucial for maintaining measurement accuracy and reliability. This study examines the impact of phase centre variation (PCV) corrections on zenith wet delay (ZWD) accuracy in precise point positioning (PPP) solutions using low‐cost systems. The results show that PCV corrections significantly improve ZWD estimation, reducing bias and RMS by 66% and 31% in ambiguity float PPP, and by 71% and 38% in ambiguity fixed PPP. In addition, integer ambiguity resolution offers no significant improvement in ZWD accuracy without PCV correction. When PCV corrections and ambiguity fixing are applied, low‐cost receivers demonstrate ZWD estimates comparable to those of high‐precision geodetic receivers, with a deviation of 0.2 mm and an RMS of 2 mm. However, variations in signal tracking and multipath suppression can still influence ambiguity fixing rates, resulting in slightly lower performance for low‐cost receivers compared to their high‐precision counterparts. The study concludes that deploying low‐cost receivers with calibrated antennas offers a cost‐effective approach to increasing the spatial resolution of atmospheric water vapour measurements, thereby enhancing weather monitoring and early warning systems, particularly for localised extreme weather events. [ABSTRACT FROM AUTHOR]

The use of global navigation satellite systems (GNSS) technology within the fields of ecology and biology has increased over recent years. With Global Positioning System, GLObalnaya NAvigatsionnaya Sputnikovaya Sistema, Galileo, and BeiDou systems fully deployed, >140 navigation satellites are currently available for navigation and high precision positioning applications. The technological improvements in GNSS devices, mainly due to the multi‐frequency capability, reduce signal acquisition time and increase the reliability, the continuity, and the accuracy of the estimated position, especially in complex environments like forests or areas with a steep topography. This study aims to test experimentally the influence of multi‐constellation multi‐frequency modules on the performance of the GNSS collars used to monitor wildlife. We applied static and kinematic tests designed to assess and compare the performance of GNSS collars equipped with a single‐frequency versus a multi‐frequency chipset. We evaluated the availability and continuity of solutions, number of satellites used, dilution of precision, precision, accuracy, and repeatability of these quality parameters for GNSS devices in southeastern Spain from February 2021 to June 2022. The results confirmed that the multi‐constellation multi‐frequency GNSS collar showed a stable and good performance in terms of the number of satellites used (>10), horizontal dilution of precision (<1.3), fix success rate (100%), mean location error (<1.5 m), and circular error probability (CEP), which was better by approximately one order of magnitude than the single‐frequency collar (1–10 m). The use of reliable and accurate GNSS devices will expand our knowledge of animal behavior and the interactions between species. Multi‐frequency GNSS collars allow collection of accurate locations, providing fine‐scale information about animal behavior (e.g., feeding strategies, competition for resources), whereas the single‐frequency GNSS collars can used for broad‐scale studies (e.g., home ranges, habitat use). [ABSTRACT FROM AUTHOR]

ESA's Swarm constellation entered in a "overfly" configuration in the period between September and October 2021, when the longitudinal distance between the lower pair and the upper satellite was at its minimum since the launch of the spacecrafts. In addition, the local time of the nighttime tracks was favorable to detect and study the morphology of post‐sunset equatorial plasma bubbles (EPBs). In this study, we focus on the Swarm overfly occurring between 00:41 UT and 00:59 UT on 30 September 2021, which covered one of the most densely instrumented regions for the study of the ionospheric irregularities embedded in the EPBs: the South American sector. By exploiting the use of ground‐based receivers of Global Navigation Satellite System (GNSS) signals in combination with the Swarm plasma density measurements, we study the irregularities in the EPB formed at ∼60°W and investigate the different scales of the irregularities and the cascading processes along the magnetic flux tubes. We also highlight how diffusion along the magnetic field lines occurs simultaneously with the plasma uplift, contributing then to the correct interpretation of the EPB evolution and decay process. The precious overfly conditions also allow the introduction of ionosphere‐related quantities, evaluated across the tracks at satellite altitudes enlarging the possibilities given by the same quantities already available along the tracks. Such opportunity envisages the possibility to proxy the impact of EPBs on GNSS signals with Low‐Earth Orbit satellite data provided by future missions specifically dedicated to the characterization of the near‐Earth environment and ionospheric studies. Plain Language Summary: Ionospheric Equatorial Plasma Bubbles (EPBs) are the most dangerous threat to radio‐wave propagation in the frequencies from HF, used for telecommunications, to L‐band, emitted by Global Navigation Satellite Systems (GNSS). Such bubbles form in the post‐sunset hours at equatorial latitudes and their occurrence is still a challenge for the scientific community, in terms of capability to model their triggering mechanisms, formation, growth and decay. On 30 September 2021, a precious occasion occurred. The 3 satellites constituting the ESA's Swarm constellation—a set of three satellites, two orbiting at 440 km and flying in pairs and one at 510 km—entered in a "overfly" configuration over Brazil. In other words, the lower pair and the upper satellite flew in a narrow longitudinal band and in one of the most densely instrumented regions in terms of ground‐based GNSS receiver. This translated into the possibility to step into a single EPB. We exploited this configuration and the ground‐based measurements to provide an unprecedented reconstruction of a plasma bubble and to introduce new measurements that can be used by future satellite missions to provide insights on the most dangerous natural hazard to radio waves. Key Points: Swarm overfly allowed offers an unprecedented possibility to investigate the features of a single plasma bubble at different altitudesScales of the irregularities and their cascading processes along the magnetic flux tubes are identifiedIonosphere‐related quantities, evaluated across the tracks at different satellite altitudes, are introduced [ABSTRACT FROM AUTHOR]

Aiming to improve the position and velocity precision of the INS/GNSS system during GNSS outages, a novel system that combines unscented Kalman filter (UKF) and nonlinear autoregressive neural networks with external inputs (NARX) is proposed. The NARX‐based module is utilized to predict the measurement updates of UKF during GNSS outages. A new offline approach for selecting the optimal inputs of NARX networks is suggested and tested. This approach is based on mutual information (MI) theory for identifying the inputs that influence each of the outputs (the measurement updates of UKF) and lag‐space estimation (LSE) for investigating the dependency of these outputs on the past values of the inputs and the outputs. The performance of the proposed system is verified experimentally using a real dataset. The comparison results indicate that the NARX‐aided UKF outperforms other methods that use different input configurations for neural networks. [ABSTRACT FROM AUTHOR]

Long‐term thermospheric mass density disturbances due to magnetospheric forcing are not clear due to a lack of measurement data and imprecise models. In this study, the Global Navigation Satellite System (GNSS) precise orbits of CAScade SmallSat and IOnospheric Polar Explorer (CASSIOPE) are used to infer high‐resolution thermospheric mass densities between the years 2014 and 2020. The CASSIOPE densities are comprehensively validated at altitudes from 325 to 425 km at intervals of 25 km with the High Accuracy Satellite Drag Model (HASDM) density database, and further compared with the Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Exosphere/2000 (NRLMSISE‐00) and the Jacchia‐Bowman/2008 (JB2008) empirical models. The CASSIOPE densities are very similar to the HASDM and JB2008 densities, while the NRLMSISE‐00 largely overestimates (∼150%) during low solar‐flux conditions. For density values above ∼10−12 kg/m3, the correlation of CASSIOPE with HASDM is ∼5% better than the models, and the standard deviation is within 10% of the background density. For density values below ∼10−12 kg/m3, systematic errors have shown to reduce the precision of the CASSIOPE densities. By setting geomagnetic contributions to zero in the models, the density disturbances due to magnetospheric forcing are isolated from the CASSIOPE time‐series, allowing investigation into the correlations and time‐delay responses to the models and to the merging electric field (Em). A new linear dependence of the time delay to the Em was found and then parameterized in this study. Time delays occurred at the 4–7 h range during geomagnetic storms, and at 9–11 h during quiet conditions; neither had significant dependence on altitude. The results represent the validation of the first high‐resolution thermospheric mass density estimates inferred from commercial‐off‐the‐shelf GNSS receivers. Key Points: Thermospheric mass densities from 2014 to 2020 are estimated from CAScade SmallSat and IOnospheric Polar Explorer Global Navigation Satellite System (GNSS) precise orbitsThe high‐resolution thermospheric mass densities inferred from commercial‐off‐the‐shelf GNSS receivers are validatedThe density disturbances due to magnetospheric forcing are investigated for correlations and time‐delay responses to models and indices [ABSTRACT FROM AUTHOR]

Precise point positioning (PPP) uses precise satellite orbits, clock corrections and biases derived from a global network of reference stations to enable accurate positioning worldwide. Natural Resources Canada's Canadian Spatial Reference System (CSRS) PPP is a free Web service offering automated PPP processing. A critical factor limiting the adoption of PPP in many applications is the convergence time needed to reach centimeter‐level accuracies. To address this issue, CSRS‐PPP now implements PPP with ambiguity resolution (PPP‐AR). This feature required the development of new algorithms, such as sequential normal stacking for least‐squares filtering/smoothing, and the weighted integer decision concept for ambiguity validation. New satellite product lines (ultra‐rapid, rapid, final) also have been deployed to enable PPP‐AR processing with various latencies. This analysis demonstrates that sub‐centimeter horizontal accuracies can be obtained in less than one hour for both static and kinematic modes. Using product lines with longer latencies is beneficial, although improvements are typically within the reported uncertainties. [ABSTRACT FROM AUTHOR]

Performance of global navigation satellite systems (GNSSs) mounted on aerial platforms could be degraded by the presence of jamming or spoofing threats. Detection of jamming and spoofing is essential considering practical applications of satellite navigation in passenger aircrafts, unmanned aerial vehicles (UAVs), helicopters and fighters. Different algorithms and methods have been proposed for detection of these threats; however, their usage has many limitations because of their demanding weight, size and computational complexity, when embedded on aerial systems. In this study, the authors develop a theoretical framework to detect the presence of the threat of UAVs. The idea is based on the fact that, due to the UAV motion, the samples of received signal power from a fixed threat and from a GNSS satellite have different empirical probability density functions. Moreover, by using two antennas (an omnidirectional and a down‐tilted‐directional), they introduce a new method to distinguish between aerial and ground‐based threats. The proposed algorithms have a low‐computational burden and can consider the fading loss as well. Simulation results show the superior performance of the proposed methods, in terms of detection and false alarm probability, compared to the existing methods. [ABSTRACT FROM AUTHOR]

Design of a multiband circularly polarized antenna is proposed in this article. The antenna has a simple and compact form factor by employing single‐feed stacked patch structure. It exhibits good performance at the global navigation satellite system (GNSS) frequency bands of L1, L2, and L5 and cellular communications frequency band of 2.3 GHz. The antenna has a 3‐dB axial ratio bandwidth of 1.1%, 1.0%, 4.1%, and 1.5% at the four operating bands of L1 (1.575 GHz), L2 (1.227 GHz), L5 (1.176 GHz), and 2.3 GHz. The antenna also achieves a gain of more than 2.2 dBiC and efficiency of more than 70% at the four frequencies. A detailed parametric study is carried out to investigate the importance of different structural elements on the antenna performance. Results are verified through close agreement of simulations and experimental measurements of the fabricated prototype. Good impedance matching, axial ratio bandwidth, and radiation characteristics at the four operating bands along with small profile and mechanically stable structure make this antenna a good candidate for current and future GNSS devices, mobile terminals, and small satellites for 5G/Beyond 5G (5G/B5G) applications. [ABSTRACT FROM AUTHOR]

The electron content distribution of the north and south polar ionosphere from 2001 to the beginning of 2019 is analyzed by using the UQRG global ionospheric map (GIM) of vertical total electron content (VTEC), computed every 15 min by UPC‐IonSAT with a tomographic‐kriging combined technique. We first show that the accuracy of UQRG GIM is slightly better than that of the GIMs of other analysis centers on the whole and also over both poles. Second, we show examples of polar VTEC features in UQRG GIM, previously reported by different authors and with higher‐resolution techniques. Third, by means of an unsupervised clustering algorithm, learning vector quantization, we characterize the main features of the ionospheric electron content climatology, separately for the north and south polar regions. Key Points: The UPC GIM has been analyzed over both poles during 1.5 solar cycles confirming its slightly better performance compared to other IGS GIMsIt presents realistic VTEC features over two poles, in agreement with previous higher resolution works and using non‐GNSS measurementsThe climatology of the main VTEC polar features is obtained by means of the learning vector quantization (LVQ) unsupervised technique [ABSTRACT FROM AUTHOR]

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]

The medium-scale traveling ionospheric disturbances (MSTIDs) constitute the most frequent ionospheric wave signatures. We propose a method for detecting the number of simultaneous MSTIDs from a time series of high-pass-filtered Vertical Total Electron Content (VTEC) maps and their parameters. The method is tested on the VTEC map corresponding to a simulated realistic scenario and on actual data from dual-frequency Global Positioning System (GPS) measurements gathered by +1200 GPS receivers of the GPS Earth Observation Network (GEONET) in Japan. The contribution consists of the detection of the number of independent MSTIDs from a nonuniform sampling of the ionospheric pierce points. The problem is set as a sparse decomposition on elements of a dictionary of atoms that span a linear space of possible MSTIDs. These atoms consist of plane waves characterized by a wavelength, direction, and phase on a surface defined, the part of the ionosphere sounded by the GEONET (i.e., 25°N to 50°N of latitude and 125°E to 155°E of longitude). The technique is related to the atomic decomposition and least absolute shrinkage and selection operator. The geophysical contribution of this paper is showing (a) the detection of several simultaneous MSTIDs of different characteristics, with a continuous change in the velocity; (b) detection of circular MSTID waves compatible by time and center with a specific earthquake; (c) simultaneous superposition of two distinct MSTIDs, with almost the same azimuth; and (d) the presence at nighttime of MSTIDs with velocities in the range 400-600 m/s. [ABSTRACT FROM AUTHOR]

We present analysis methods for studying the structuring and motion of ionospheric irregularities at the subkilometer scale sizes that produce L band scintillations. Spaced-receiver methods are used for Global Navigation Satellite System (GNSS) receivers' phase measurements over approximately subkilometer to kilometer length baselines for the first time. The quantities estimated by these techniques are plasma drift velocity, diffraction anisotropy magnitude and orientation, and characteristic velocity. Uncertainties are quantified by ensemble simulation of noise on the phase signals carried through to the observations of the spaced-receiver linear system. These covariances are then propagated through to uncertainties on drifts through linearization about the estimated values of the state. Five receivers of SAGA, the Scintillation Auroral Global Positioning System (GPS) Array, provide 100 Hz power and phase data for each channel at L1 frequency. The array is sited in the auroral zone at Poker Flat Research Range, Alaska. A case study of a single scintillating satellite observed by the array is used to demonstrate the spaced-receiver and uncertainty estimation process. A second case study estimates drifts as measured by multiple scintillating channels. These scintillations are correlated with auroral activity, based on all-sky camera images. Measurements and uncertainty estimates made over a 30 min period are compared to a collocated incoherent scatter radar and show good agreement in horizontal drift speed and direction during periods of scintillation for which the characteristic velocity is less than the drift velocity. [ABSTRACT FROM AUTHOR]

Magnetic noise originating from the ionosphere may be estimated by using the total electron concentration data retrieved by the global navigation satellite systems. This provides a useful scheme for mitigation of magnetic noise coming from the fluctuating ionosphere, which is a major interference source in the magnetic anomaly detection applications. [ABSTRACT FROM AUTHOR]

In high‐precision relative positioning applications of global navigation satellite systems, multipath and phase centre offset/variation remain as the major coupled error sources, as they cannot be eliminated by the differential operation. A circular rotating low‐cost antenna is introduced for the rover station in a constrained environment. The spatial diversity of multipath is explored by circular motion to aid the carrier‐phase ambiguity resolution and error elimination. The multipath and phase centre offset are separated and estimated. Field tests demonstrate that the proposed method with low‐cost antenna is able to achieve the survey‐grade precision. [ABSTRACT FROM AUTHOR]

Signal acquisition has become the performance bottleneck of global navigation satellite systems (GNSS) receivers in harsh interference environments due to its low sensitivity. In this Letter, a novel anti‐jamming algorithm based on the minimum mean square error criterion is proposed to protecting the acquisition stage. The key idea behind the proposed method is that the grid search process of synchronisation parameters is shared by both interference suppression and signal acquisition. Simulation results indicate that the proposed method is capable of maintaining the functionality of GNSS receivers at cold start in the presence of interfering signals. In addition to this, its performance outperforms the power inversion method significantly. [ABSTRACT FROM AUTHOR]

A novel compact monopole antenna with wide circularly polarised (CP) bandwidth is designed, fabricated and measured. The wide impedance bandwidth and broadband CP characteristic are achieved based on a simple tilted monopole structure, which consists of a slotted rectangular patch and an improved ground plane. The measured impedance bandwidth with return loss better than 10 dB is 97.4% (1.10–3.19 GHz), the measured 3 dB axial‐ratio bandwidth is 59.1% (1.11–2.04 GHz) and the measured peak gain within the operating band is 4.84 dBic, which indicates that it is a good candidate for the application of various global navigation satellite systems. [ABSTRACT FROM AUTHOR]

A new type of tiered code for designing the ranging signal structure of global navigation satellite systems (GNSSs) is proposed. The proposed tiered code structure combines a constant amplitude zero autocorrelation polyphase secondary code with its primary code, resulting in a tiered polyphase code (TPC) that avoids cross‐correlation interference between different ranging codes. The analysis and the simulation results show the performance of the proposed TPC and confirm its effectiveness as a ranging signal structure for the GNSSs. [ABSTRACT FROM AUTHOR]