GNSS Network Research Articles

Stacking machine learning model for precipitable water vapor vertical adjustment using GNSS networks and radio occultation data

Stacking machine learning model for precipitable water vapor vertical adjustment using GNSS networks and radio occultation data

Successively Equatorward Propagating Ionospheric Acoustic Waves and Possible Mechanisms Following the Mw 7.5 Earthquake in Noto, Japan, on 1 January 2024

AbstractOn 1 January 2024, the Mw 7.5 Noto Peninsula earthquake in Japan generated ionospheric disturbances detected via dense GNSS networks. Significant coseismic acoustic waves emerged ∼8 min post‐event, exhibiting 0.3 TECU amplitudes, 2–8 min periods, and ∼1 km/s propagation speeds. These disturbances propagated exclusively southward as arc‐shaped fronts. The observed anisotropy aligns closely with the local geomagnetic field orientation (declination 8.7°), suggesting magnetic channeling as a key factor. Secondary factors likely include northward thermospheric winds suppressing northward wave propagation and land‐ocean coupling efficiency differences, which enhanced vertical displacements over southern continental regions. Notably, weak disturbances linked to the Mw 6.2 aftershock were detected, challenging conventional magnitude thresholds for ionospheric detection. While the mainshock's CID dynamics reflect known magnetic guidance mechanisms, the southward preference highlights site‐specific interactions between seismic forcing and geophysical filters. This study provides new observational evidence of earthquake‐ionosphere coupling, emphasizing the detectability of moderate‐magnitude events under favorable conditions, with implications for space weather monitoring and multi‐scale seismic hazard assessment.

Spatiotemporal patterns of accumulation and surface roughness in interior Greenland with a GNSS-IR network

Abstract. The dry-snow zone is the largest region of the Greenland Ice Sheet, yet temporally and spatially dense observations of surface accumulation and surface roughness in this area are lacking. We use the global navigation satellite system interferometric reflectometry (GNSS-IR) technique with a novel, low-cost GNSS network of 12 stations in the vicinity of the ice sheet summit to reveal temporal and spatial patterns of accumulation of the upper snow layer. We show that individual measurements are highly precise (±2.8 cm), while the aggregate of hundreds of daily measurements across a large spatial footprint can detect millimeter-level surface changes and is biased by -2.7±3.0 cm compared to a unique validation data set that covers a similar spatial extent to the instrument sensing footprint. Using the validation data set, we find that the reflectometry technique is most sensitive to the surrounding 4–20 m of the surface, with the GNSS antenna at a height of 1–2 m above ground level. Along with an exceptionally high accumulation rate at the beginning of the study, we also detect an across-slope dependence in accumulation rates at yearly timescales. For the first time, we also validate GNSS-IR sensitivity to meter-scale surface heterogeneities such as sastrugi, and we construct a time series of surface roughness evolution that suggests a seasonal pattern of heightened wintertime roughness features in this region. These surface accumulation and roughness measurements provide a novel data set for these critical variables and show a statistically significant relationship with occurrences of both high winds and precipitation events but only moderate correlations, suggesting that other processes may also contribute to accumulation and enhanced surface roughness in the interior region of Greenland.

Constancy of Geologic and Geodetic Fault Slip Rates Across the Arabia‐Eurasia Collision Revealed Through Two Decades of Observation

AbstractWhether the decadal accumulation of strain across active faults is representative of the long‐term rate of fault slip is a central and unresolved issue within active tectonics and earthquake science and is an issue of societal as well as academic interest. Significant variability in slip rate is often reported, and there is remaining uncertainty in the transferability between the two timescales of measurement. In this study, we examine the active fault systems across Iran, a region that is deforming due to the ongoing continental collision between Arabia and Eurasia. We compile all existing geological slip rates on strike‐slip faults within the region and compile/determine geodetic rates across the faults from GNSS networks and, in a few cases, from InSAR‐derived velocity fields. When the data set is taken as a whole we find agreement between the geological and decadal measurements, showing no resolvable differences in rate as averaged over decadal, Holocene (10 ka), and late Pleistocene (10–100 ka) time periods, with outliers from this trend likely resulting either from methodological limitations in individual studies or from assumptions of the age of offset landform features, which tend to underestimate the fault rate. Our study confirms that decadal measurements of strain accumulation are representative of long‐term accumulation of fault slip, at least within the uncertainties of our measurements in the Iranian plateau.

Resonant Infrasonic Disturbances in Total‐Electron‐Content During a Severe Thunderstorm on 23 October 2021

AbstractDeep convective clouds and lightning activity during thunderstorms imprint Infrasonic (3 mili Hertz) oscillations in the ionospheric density or Traveling Ionospheric Disturbances (TIDs). The wave characteristics of these oscillations and the coupling mechanisms remain a subject of investigation, noting that the coupling energetics may alter the spectral and propagation characteristics. Moreover, the availability of numerous convective dynamics time scales makes the oscillation detection time uncertain. To study these aspects, the present work examines the spatial‐temporal lightning flash rate during a severe thunderstorm (cloud top temperature −80°C) from the GOES16 infrared channel and the total electron content of the ionosphere from the GNSS network over the tropical Southern Hemisphere. The study finds TIDs amplification above the deep convective clouds. The strongest amplification occurs at the earliest, at 9 min, from the most intense lightning flash rate and propagates at the most probable speed of 400–1,100 m/s. In contrast to the spectral peak of the active storm, which is 1.2 mHz, the spectral peak of TIDs is 4.8 mHz. The results highlight the magnitude of coupling energetics to determine the wave propagation characteristics of infrasonic TIDs.

Correction: A meta-classification-based approach for outlier identification in GNSS networks

Correction: A meta-classification-based approach for outlier identification in GNSS networks

Assessing the data quality and seismic monitoring capabilities of the Belt and Road GNSS network

Assessing the data quality and seismic monitoring capabilities of the Belt and Road GNSS network

A Regional Gravimetric and Hybrid Geoid Model in Northern Greece from Dedicated Gravity Campaigns

The determination of physical heights is of key importance for a wide spectrum of geoscientific applications and, in particular, for engineering projects. The main scope of the present work is focused on the determination of a high-accuracy and high-resolution gravimetric and hybrid geoid model, to determine orthometric heights without the need of conventional leveling. Both historical and newly acquired gravity data have been collected during dedicated gravity campaigns, around the location of a dedicated GNSS network as well as areas where the existing land gravity database presented voids. Geoid determination was based on the classical remove–compute–restore (RCR) technique and spectral and stochastic approaches. The low frequencies have been modeled based on the XGM2019e global geopotential model (GGM) and the topographic effects have been evaluated with the residual terrain model (RTM) reduction. The evaluation of the final geoid model was performed over 462 GNSS/leveling benchmarks (BMs), where the newly determined gravimetric geoid has shown an improvement of 3.1 cm, in the std of the differences to the GNSS/leveling BMs, compared to the latest national geoid model. A deterministic and stochastic fit to the GNSS/leveling data has been performed, investigating various choices for the parametric models and analytical covariance functions. The scope was to determine a hybrid geoid model, tailored to the area and GNSS/leveling data, which will be the one used for the direct estimation of high-accuracy orthometric heights from GNSS observations. After the deterministic fit, a std to the GNSS/leveling data of 10.1 cm has been achieved, with 54.8% and 83.1% of the absolute height differences being below the 1 cm and 2 cm per square root km of baseline length. The final hybrid geoid model, i.e., after the stochastic treatment of the adjusted residuals, gave a std of the difference to the GNSS/leveling data of 1.1 cm, with 99.8% and 99.9% of the height difference being smaller than the 1 cm and 2 cm standard errors, thus achieving a 1 cm accuracy regional geoid.

Two‐ and Three‐Dimensional Propagation Characteristics of Co‐Volcanic Ionospheric Disturbances Induced by the 2022 Tonga Volcano Eruption Using Dense GNSS Network Data

AbstractOn 15 January 2022, the submarine volcano in Hunga Tonga‐Hunga Ha’apai (hereinafter Tonga volcano) erupted at 04:14 universal time. This study investigated the two‐ and three‐dimensional co‐volcanic ionospheric disturbances (CVIDs) induced by the strong Tonga volcano. Based on dense Global Navigation Satellite System network data in Australia, the two‐dimensional detrended total electron content maps were first generated by using the Savitzky‐Golay filtering method. Using a compressed sensing‐based computerized ionospheric tomography approach, the three‐dimensional ionospheric electron densities were reconstructed. After the eruption, the distinctive CVIDs began to be mostly observed over southeastern Australia, about 4,000 km from the volcano. Two patterns of observable CVIDs, that is, fast‐mode and slow‐mode CVIDs, traveled outward from the Tonga volcano at speeds of 600–850 and 200–350 m/s, respectively. The slow‐mode CVIDs were related to the Lamb and secondary gravity waves, while the fast‐mode CVIDs were related to acoustic waves. Three‐dimensional reconstruction results demonstrated that as the CVIDs propagated upward, the electron densities fluctuated at most altitude‐longitude slices, and the wave‐like propagating patterns were clearly observed around the peak ionospheric heights of 260–340 km. At the peak ionospheric height, the ionospheric parameters derived from the two ionosondes over Australia also detected similar wave‐like features. Two‐dimensional and three‐dimensional observational evidence of the Tonga‐induced CVIDs enhances research on volcanic eruption effects over the upper ionosphere.

Global Ionospheric Scintillation Estimation Based on Phase Screen Modeling From One‐Dimensional Satellite Data

AbstractIonospheric scintillations, which usually manifest as sudden, rapid fluctuations in radio wave signal phase and amplitude, challenge the reliability of satellite communication and navigation. Based on the single phase screen assumption, this study uses the one‐dimensional (1D) in‐situ plasma density data of ESA's Swarm constellation data to develop a three‐dimensional (3D) power spectrum of electron density perturbation and construct a model to estimate scintillations caused by small‐scale ionospheric plasma density irregularities. By deriving the turbulence strength () and calculating the amplitude scintillation index S4, the global distribution of ionospheric scintillation is derived. Scintillation from our model shows typical seasonal variations, with peaks during equinoxes at both high and low magnetic latitudes. For local time (LT) dependence, the scintillation at low magnetic latitudes peaks around 21:00 LT, while at high magnetic latitudes, the maximum occurrence appears around noon, with an asymmetry between the northern and southern hemispheres. In addition, positive correlations between scintillation occurrence and solar activity, as well as geomagnetic storms are observed, with higher magnetic latitudes more being affected by geomagnetic disturbances. These features of our model‐estimated scintillations agree well with the occurrence of small‐scale plasma density irregularities at different magnetic latitudes as reported by previous studies. Our study introduces a way to estimate the global coverage of ionospheric scintillation from in‐situ satellite measurements, which cannot be achieved by the ground‐based GNSS networks due to the lack of coverage in the ocean regions.

Recent movements of the Earth's surface of the Сarpathian mountain system according to GNSS data

The purpose of the research is differentiation of recent geodynamic processes within the Carpathian Mountains on the basis of freely available GNSS data. Methodology. The methodology included GNSS data collection, processing and analysis. An algorithm for processing was proposed, which consisted of 5 main stages: transformation of data into an internal format, verification of time series for compliance with requirements, determination of horizontal velocities, division of the GNSS network into triangles, and determination of deformation parameters. Results. This study presents a comprehensive analysis of recent geodynamic processes based on GNSS data freely available from the Nevada Geological Survey. Taking into account the requirements for time series, 50 GNSS stations were selected and processed. In general, absolute and regional velocities were obtained and analysed during 2000–2023. Regional velocities of horizontal movements were used to calculate the deformation tensor and deformation parameters. The results of the study are consistent and correlate well with the studies of other scientists. The obtained results confirm the presence of active geodynamic processes within the Carpathians. Originality. The proposed approach made it possible to estimate the main deformation parameters (value and direction of deformation axes, total shear and dilation) within the Carpathian Mountains. This makes it possible to analyse and predict recent geodynamic processes in the region. Practical significance. On the basis of the calculated values, maps of the distribution of vectors of absolute and regional horizontal velocities, total shear rates, dilatation rates, and rotation rates were constructed.

Variations of Equatorial Plasma Bubbles Behaviour in Southeast Asia: Insights from Geomagnetically Quiet Days

Abstract The present study aims to investigate the behaviour of equatorial plasma bubbles (EPBs) during quiet days in Southeast Asia (SEA). The behaviour of EPB was determined by observing their number (n) and zonal drift velocity (VE) from 2011 to 2013. The variation of the n and VE during quiet days was investigated monthly and seasonally each year. Three networks which are Malaysia Real-Time Kinematics GNSS Network (MyRTKnet), Sumatran GPS Array networks (SuGAr) and International GNSS Service (IGS) in SEA that consists of 127 receivers were utilized to collect the high-density GPS data. The data were then used to generate the zonal keogram of the rate of total electron content index (ROTI) to estimate n and VE. From the observed data, there were 376 days characterized as geomagnetically quiet according to the Kp index, with a total of 2592 EPBs observed using ROTI keogram. The highest VE was found to be ∼126 m/s during the equinox, while the lowest was ∼65 m/s in December solstice. In addition, the maximum and minimum n throughout the period were 1937 during the equinox and 163 in December solstice, respectively. While a distinct diurnal pattern emerged for n throughout 2011 until 2013, a clear diurnal pattern of VE was only evident in 2013. This observation suggests a potential link between the year with a diurnal VE pattern and the continuous presence of EPB.

Development of a high-resolution ionospheric VTEC model over Nigeria using spherical harmonics with orthogonal transformation solution

Abstract One important ionosphere element that impacts radio signal transmission is the Vertical Total Electron Content (VTEC). Accurate estimation of VTEC is important for diverse applications such as satellite positioning, space weather forecasting, satellite communication. In regions with a sparse network of receivers, especially Nigeria, the spatial and temporal resolutions of the Global Ionospheric Maps (GIM) regularly provided by the International GNSS Service (IGS), Center for Orbit Determination in Europe (CODE), and the International Reference Ionosphere (IRI) are limited. This limits their potential to uncover local ionospheric phenomena in such areas. To address this limitation, we have developed a VTEC model for estimating high temporal-resolution VTEC and Differential Code Bias (DCB) over Nigeria using spherical harmonic expansions with an orthogonal transformation solution. Our novel method makes use of GNSS measurements from the Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS) to precisely estimate VTEC and DCB. GNSS datasets in Receiver Independent EXchange (RINEX), satellite orbit (SP3) and Ionospheric Exchange (IONEX) formats from 2011 across 9 GNSS receivers in the Nigerian Geodetic Network sampled at 30-second intervals were used for this study. For this investigation, code pseudo-range observations were also smoothed using carrier phase observations. To assure data quality, we also carried out several preprocessing procedures utilizing the Melbourne-Wubbena linear and geometry-free linear combinations using an internal ITB-GNSSTEC FORTRAN application based on batch processing and least squares approaches. To validate our model, we compared the estimates with the IGS, CODE, and IRI-2020 models. Results demonstrated strong agreement with the other models with a standard deviation between 2.80 and 6.50 TECU and a correlation coefficient of not less than 0.92 at the evaluation stations. Notably, the new model aligned more closely with CODE and IGS than the IRI model. Also, the new model enabled the detection of local ionospheric VTEC post-sunset enhancement missed by GIM models. Our model also showed a strong positive correlation with the other models for quiet and disturbed days of geomagnetic activity. In Conclusively, this research has developed a high-resolution VTEC method for areas with sparse distribution of GNSS receivers, achieving a temporal resolution of 10 minutes. The ionospheric modeling in areas like Nigeria with sparse GNSS networks has greatly benefited from this research. The approach improves the precision of GNSS-based applications, such as location and navigation, by precisely calculating VTEC and DCBs. It also addresses the issue of sparse observational data in equatorial regions, offering insightful information for atmospheric and geodetic research.

Preliminary Investigation on Local Solid Earth Tides Variations in Sumatra Island Using Ina-CORS GNSS Network

Abstract Solid earth tides refer to the periodic motion of the Earth’s crust caused by the gravitational forces of the Sun and Moon. In precise geodetic measurements, solid earth tides are a critical source of error that must be mitigated to achieve high accuracy. This study aims to observe variations in local solid earth tides during two significant time periods: when the Earth is at its closest point to the Sun (Perihelion) and at its farthest point (Aphelion). We used multi-day Kinematic Precise Point Positioning (KPPP) to process kinematic data, effectively eliminating discontinuities at day boundaries. Additionally, harmonic analysis with the least squares method was applied to extract tidal generation coefficients in three directions of motion. These coefficients were then compared with theoretical models of solid earth tides, focusing primarily on the largest tidal generation coefficients for amplitude and phase values to identify local variations. Our findings reveal that the lunar semidiurnal coefficient (M2) is the primary tide generator, exhibiting the highest energy percentage. Furthermore, during the Aphelion and Perihelion periods, our results showed no significant differences in tidal ranges at a 95 percent confidence level, indicating that the Sun’s influence on these tidal variations is minimal. Additionally, we compared the differences between observed M2 coefficients, and the theoretical model provided by the International Earth Rotation and Reference Systems Service (IERS) and found discrepancies that led to large tidal residuals, suggesting that local factors, such as geological features, are not fully captured by global models. In conclusion, this study provides valuable insights into understanding local solid earth tides on Sumatra Island.

Recent deformations of the Earth's crust in Ukraine based on GNSS network data from GEOTERRACE AND SYSTEM.NET

Recent deformations of the Earth's crust in Ukraine based on GNSS network data from GEOTERRACE AND SYSTEM.NET

EVALUATION OF INTERPOLATION METHODS FOR GNSS VELOCITIES IN CRUSTAL DEFORMATION: A CASE STUDY ON STRAIN RATE CALCULATION IN THE SOUTHERN SUMATRA

This study evaluates three interpolation methods—Inverse Distance Weighting (IDW), Kriging, and Sandwell—for analyzing crustal deformation in southern Sumatra, focusing on the on-site velocity consistency test. This test is crucial for assessing interpolation accuracy by comparing interpolated velocities to actual GNSS velocities at specific sites. Given the region's sparse GNSS network, accurate interpolation is vital for reliable deformation analysis. GNSS data from continuous and campaign sites, collected between 2017 and 2022 with a 30-second sampling interval, were processed to generate velocity. The Sandwell method, particularly with a Poisson’s ratio of 0, demonstrated superior performance, achieving the lowest mean residuals in the on-site velocity consistency test. This method consistently provided accurate interpolated velocities that closely matched original site data. IDW and Kriging methods also showed effectiveness but had different convergence behaviors: IDW required higher interpolation degrees for accuracy, while Kriging excelled in the east-west residuals. The Sandwell method’s velocities were used to calculate strain rates, revealing significant spatial variability. The findings underscore the importance of detailed on-site velocity consistency testing and highlight the need for expanding GNSS networks to improve accuracy and better assess seismic hazards in southern Sumatra.

Retrieval of refractivity fields from GNSS tropospheric delays: theoretical and data-based evaluation of collocation methods and comparisons with GNSS tomography

This paper focuses on the retrieval of refractivity fields from GNSS measurements by means of least-squares collocation. Collocation adjustment estimates parameters that relate delays and refractivity without relying on a grid. It contains functional and stochastic models that define the characteristics of the retrieved refractivity fields. This work aims at emphasizing the capabilities and limitations of the collocation method in modeling refractivity and to present it as a valuable alternative to GNSS tomography. Initially, we analyze the stochastic models in collocation and compare the theoretical errors of collocation with those of tomography. We emphasize the low variability of collocation formal variances/covariances compared to tomography and its lower dependence on a-priori fields. Then, based on real and simulated data, we investigate the importance of station resolution and station heights for collocation. Increasing the network resolution, for example, from 10 to 2 km, results in improved a-posteriori statistics, including a 10% reduction in the error statistic for the retrieved refractivity up to 6 km. In addition, using additional stations at higher altitudes has an impact on the retrieved refractivity fields of about 1 ppm in terms of standard deviation up to 6 km, and a bias reduction of more than 3 ppm up to 3 km. Furthermore, we compare refractivity fields retrieved through tomography and collocation, where data of the COSMO weather model are utilized in a closed-loop validation mode to simulate tropospheric delays and validate the retrieved profiles. While tomography estimates are less biased, collocation captures relative changes in refractivity more effectively among the voxels within one height level. Finally, we apply tomography and collocation to test their capabilities to detect an approaching weather front. Both methods can sense the weather front, but their atmospheric structures appear more similar when the GNSS network has a well-distributed height coverage.

Modeling of regional GNSS network using adaptive boosting algorithm: a case study in the Xinjiang Uyghur Autonomous Region

Modeling of regional GNSS network using adaptive boosting algorithm: a case study in the Xinjiang Uyghur Autonomous Region

A meta-classification-based approach for outlier identification in GNSS networks

A meta-classification-based approach for outlier identification in GNSS networks

Active Deformation Across the Western Anatolian Extensional Province (Türkiye) From Sentinel‐1 InSAR

AbstractQuantifying interseismic deformation of fault networks which are predominantly deforming in a north‐south direction is challenging, because GNSS networks are usually not dense enough to resolve deformation at the level of individual faults. The alternative, interferometric synthetic aperture radar (InSAR), provides high spatial resolution but is limited by a low sensitivity to N‐S motion. We study the active normal fault network of Western Türkiye, which is undergoing rapid N‐S extension, using InSAR. Since most faults in the study region are normal faults, we overcome the low N‐S sensitivity by focusing on the vertical deformation component, which presents its own challenges. Sediment‐filled grabens show rapid anthropogenically induced subsidence, whereas urban areas tend toward erroneous uplift signals. Additionally, the morphological relief results in topographic and atmospheric disturbances of the InSAR signal. Our solution to these challenges is a systematic analysis of the high‐resolution vertical velocity field to deduce insights into regional deformation patterns, combined with detailed investigations of deformation along individual faults in the Western Anatolian Extensional Province. We show that tectonic deformation in the large graben systems is not restricted to the main faults. Smaller and seemingly less active faults are accommodating strain, favoring a continuum model of deformation over block models. We also observe a potential correlation between recent seismicity and active interseismic surface deformation. Observed deformation rates provide an estimate of current activity for many faults in the region. We discuss the potential and limitations of InSAR time series analysis for extensional regimes.