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The 2006 Greece earthquake epicenter (large cross) and the four IGS/EUREF reference stations used in this test case.
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The European Galileo satellite navigation system offers a signal in
space that will enable us to deduce range measurements of unprecedented
precision: the E5 broadband signal. These new code range measurements
would be up to three or four times more accurate compared to nowadays
GPS L1. However, E5 will be the only Galileo signal of that outstandin...
Context in source publication
Context 1
... 2006 Southern Greece earthquake occurred on 8 January 2006. The earthquake epicenter is shown on the map in Figure 5. Earthquake precursors can sometimes be sensed as a signal in the ionosphere under certain conditions, although the physics behind are not yet completely understood (Pulinets & Boyarchuk 2004) and are commonly considered to be a con- troversial issue. ...
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and constant value equal to 5 TECU in any observed epo...
For the purpose of building a regional (bound 20°‐60° N in latitude and 110°‐160° E in longitude) ionospheric now‐cast model, we investigated the performance of IDA4D (Ionospheric Data Assimilation Four‐Dimension) technique considering IRI (International Reference Ionosphere) model as the background. The data utilized in assimilation were slant tot...
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Precise Point Positioning (PPP) is traditionally based on dual-frequency observations of GPS or GPS/GLONASS satellite navigation systems. Recently, new GNSS constellations, such as the European Galileo and the Chinese BeiDou are developing rapidly. With the new IGS project known as IGS MGEX which produces highly accurate GNSS orbital and clock prod...
Citations
... The abrupt exploitations of GPS signals for addressing TEC variability and modeling practices are due to the diverse accessibility of ground and space-based GPS data and the all-time and all-weather GPS signal availability anywhere on or above the Earth (Hernández-Pajares et al., 2009). Recent studies emphasize on the credibility of single-frequency GPS based TEC estimations which claim reasonably comparable value to those from dual-frequency measurements (Dubey et al., 2006;Schüler and Oladipo, 2013;Hein et al., 2016). As the costs of single-frequency GNSS receivers are fairly lesser than the dual or multi-frequency GNSS receivers, number of single-frequency receivers may be employed for expanding the ionospheric TEC observation networks with moderate expenses. ...
This paper focuses on the variability of ionospheric Total Electron Content (TEC) over low latitude Indian sub-continental region during the geomagnetically quiet and disturbed periods under the high solar activity phase (years 2012 to 2015) of the 24th solar cycle. The study is carried out with Global Positioning System (GPS) observations from four International Global Navigation Satellite System Service (IGS) stations, aligned in a longitudinal fashion from magnetic equatorial location to beyond Equatorial Ionization Anomaly (EIA) crest latitude across Indian longitude. The corresponding values are extracted by four-point Inverse Distance Weighted (IDW) interpolation of TEC from IGS-Global Ionosphere Maps (IGS-GIMs) and by running the globally acceptable empirical ionosphere models: International Reference Ionosphere (IRI-2016) and Standard Plasmasphere Ionosphere Model (SPIM/IRI-Plas 2017). Apart from the manifestations of broader daytime diurnal peak TEC, its double-humped structure, EIA, winter anomaly/seasonal anomaly, and storm-time alterations, the study tried to probe the model performances with respect to the GPS based TEC observations. While GIM-TEC portrays a systematically varying magnitude for a particular location, the underestimation (equatorial latitude) and overestimation (higher latitude) is being witnessed by IRI model in the diurnal and seasonal variations. However, SPIM-2017 manifests an all-time overestimated TEC irrespective of time and season though the variation pattern replicates the GPS-TEC observations. Concerning storm-time response, the sub-models embedded in IRI/SPIM hardly reveal a remarkable alteration in the regular TEC variation except for trivial divergences in the IRI outcomes. In spite of compelling timely improvements in climatological representations, the limited storm-time response in IRI/SPIM models attracts the attention for further improvements in the existing primitive storm model specifications. Moreover, the intentional ingestion of external GPS-TEC into the SPIM-2017 model resulted in an exceptional improvement (about 75%) in the model prediction with improved correlation coefficients. The results from this study would complement a realistic global climatological representation of ionosphere for a faithful estimation of ionospheric delay error in radio signal applications. Finally, our results emphasize the flexibility of scopes in SPIM-2017 model towards external ingestions of observed ionospheric parameters. The ingestion of optional inputs convolved with rescaling and optimization would significantly improve the model performances for global climatological as well as storm-time ionospheric representation.
... Compared with the more common DF approach, an attractive advantage of the SF method is that it can work with mass-market SF receivers, which are much more costeffective than geodetic-grade DF receivers. Several studies have already been performed regarding SF GNSS retrieval of TEC (Yuan and Ou 2001;Wu et al. 2006;Schueler and Oladipo 2013), and most of the literature focuses on the code-minus-carrier (CMC) combination method. Schueler and Oladipo (2014) found that the CMC-based SF method is suitable for ionosphere monitoring for mid-and highlatitude sites; however, the precision level of CMC-based TEC estimate is bounded by the code-delay noise and multi-path effects. ...
The customary approach to determine ionospheric total electron content (TEC) with BeiDou navigations satellite system (BDS) data normally requires dual-frequency (DF) data provided by geodetic-grade receivers. In this study, we present an analysis of the performance of a new TEC estimation procedure based on single-frequency (SF) BDS data. First, the ionospheric observable is retrieved from the SF BDS code and phase data using precise point positioning (PPP) instead of the carrier-to-code leveling (CCL) technique used in the customary DF method. Then, the absolute ionospheric slant TEC (STEC) values are isolated from the ionospheric observables by modeling the ionospheric observable with the adjusted spherical harmonic (ASH) expansion and constraining the satellite differential code bias (SDCB) to very precise values provided externally. The experimental data were taken from the multi-GNSS experiment (MGEX) network for high and low sunspot periods, covering the 2 months, i.e., December 2014 and September 2017. The TEC data obtained from the combined final global ionospheric map (GIM) provided by the international GNSS service (IGS), the JASON DF altimeter, and the BDSmeasured differential STEC (dSTEC) are used as reference data to evaluate the performance of the TEC values estimated by the proposed method. The evaluation results indicate that compared to the reference TEC data, the ionospheric TEC estimated by the proposed method using BDS B1 data and the customary CCL-based DF method based on BDS B1 + B2 data, perform at roughly equal levels.
... Issler et al. [28] depicted a sequential filter algorithm only for the L1 ionospheric delay estimation. Torben and Olushola [29] proposed an approach for the retrieval of VTEC with GPS L1 and GALILEO E5 measurements. In addition, Zhang et al. [24] proposed a novel PPP-based uncombined SF approach that enables the joint estimation of VTEC and SDCBs from the original GNSS code and phase observables, and the numerical analyses clarified that the SF approach performs well when applied to GPS L1 data collected by a single receiver under both calm and disturbed ionospheric conditions. ...
The global navigation satellite system (GNSS) data are beneficial for sensing the earth's ionosphere by virtue of their temporal continuity and spatial coverage. In recent years, GNSS (GPS, GLONASS, BDS, and GALILEO) has developed rapidly, with BDS and GALILEO offering position, navigation, and timing services and the ongoing modernization of GPS and GLONASS. The customary approach to sensing the ionosphere normally uses the dual- or multifrequency (DF) data provided by geodetic-grade receivers and consists of two sequential steps. The first step is retrieving ionospheric observables using the carrier-to-code leveling technique. In the second step, using the thin-layer ionospheric model, one can isolate the main vertical total electron content (VTEC) for ionosphere sensing as well as the by-product of the satellite differential code biases (SDCBs) and the receiver differential code biases. In this paper, we proposed a multi-GNSS single-frequency (SF) precise point positioning approach enabling the simultaneous retrieval of VTEC and SDCBs with low-cost receivers. The root mean square of the VTEC differences between the values retrieved from the multi-GNSS SF method and DF method is approximately 0.5 total electron content unit in each system.
... Some researchers have estimated vertical Total Electron Content parameters using a single-frequency approach of Global Navigation Satellite System data and thereafter compared their results with those obtained from dual frequency measurements (e.g. Zhang et al., 2017;Win et al., 2016;Rao, 2017;Torben and Olushola, 2013). ...
... Note, interestingly, that, there is a vast body of literature on a single-frequency (SF) approach, estimating VTEC from the Code-Minus-Phase (CMP) observables (Cohen et al. 1992;Schüler and Oladipo 2013;Schüler and Oladipo 2014;Xia 1992). One prominent advantage over the DF approach is that the SF approach is more cost-effective because it relies upon mass-market (instead of geodetic-grade) receivers. ...
Vertical total electron content (VTEC) parameters estimated using global navigation satellite system (GNSS) data are of great interest for ionosphere sensing. Satellite differential code biases (SDCBs) account for one source of error which, if left uncorrected, can deteriorate performance of positioning, timing and other applications. The customary approach to estimate VTEC along with SDCBs from dual-frequency GNSS data, hereinafter referred to as DF approach, consists of two sequential steps. The first step seeks to retrieve ionospheric observables through the carrier-to-code leveling technique. This observable, related to the slant total electron content (STEC) along the satellite–receiver line-of-sight, is biased also by the SDCBs and the receiver differential code biases (RDCBs). By means of thin-layer ionospheric model, in the second step one is able to isolate the VTEC, the SDCBs and the RDCBs from the ionospheric observables. In this work, we present a single-frequency (SF) approach, enabling the joint estimation of VTEC and SDCBs using low-cost receivers; this approach is also based on two steps and it differs from the DF approach only in the first step, where we turn to the precise point positioning technique to retrieve from the single-frequency GNSS data the ionospheric observables, interpreted as the combination of the STEC, the SDCBs and the biased receiver clocks at the pivot epoch. Our numerical analyses clarify how SF approach performs when being applied to GPS L1 data collected by a single receiver under both calm and disturbed ionospheric conditions. The daily time series of zenith VTEC estimates has an accuracy ranging from a few tenths of a TEC unit (TECU) to approximately 2 TECU. For 73–96% of GPS satellites in view, the daily estimates of SDCBs do not deviate, in absolute value, more than 1 ns from their ground truth values published by the Centre for Orbit Determination in Europe.
Our investigation aims to answer if it is possible to detect plasma bubbles using single-frequency measurements of the Global Navigation Satellite System (GNSS). In this regard, we show a methodology based on a regional model to calibrate GNSS single-frequency measurements and derive ionospheric maps showing plasma bubbles in one of the most challenging conditions, the Brazilian region. Simultaneous observations of all-sky images at Cachoeira Paulista (22.7°S, 45.0°W), São João do Cariri (7.4°S, 36.5°W) and Boa Vista (2.8°N, 60.7°W) were used to compare the plasma bubbles structures. The results were validated by the comparison between airglow and total electron content (TEC) single-frequency maps in terms of keograms and drift velocities of the ionospheric plasma bubbles. Plasma bubbles were successfully observed by mapping TEC single-frequency. The rate of success in detecting the plasma bubbles with single-frequency TEC data was 65% when using keograms. In addition, in regions with good GNSS coverage, such as Cachoeira Paulista and São João do Cariri, it was easier to detect the plasma bubbles. The velocities of plasma bubbles were also obtained with good agreement in comparison with the velocities estimated using airglow data. For São João do Cariri, the mean drift velocities estimated with airglow data were 117.10 m/s whereas with TEC data were 117.94 m/s. Therefore, the results revealed the proposed method as an efficient tool for mapping the ionospheric plasma bubbles and computing their drift velocities. This technique provides new opportunities, in particular for ionospheric sounding, since the number of low-cost GNSS receivers continues growing.
The Global Navigation Satellite Systems GNSS retrieve data from multi-frequency and four constellations: GPS, GLONASS, GALILEO, BEIDOU. Global ionospheric models have not enough spatial resolution for regional purposes. Ecuador is located in the highest ionospheric activity zone (low latitude region). This paper aims to determinate the Vertical Total Electron Content, VTEC, from GALILEO signals to understand the ionospheric behavior above a low latitude station. We used data from EPEC (SIRGAS-CON) monitoring station from January 27th to November 4th, 2019 (281 days). VTEC measurements were obtained from GALILEO signals E1 and E5a and GPS signals L1 and L2. Time series used hourly data. Results showed VTEC for GALILEO varied between 22,19 and 37,47 TECU and VTEC for GPS varied between 35,55 and 50,15 TECU. Maximum VTEC measurements reached in April 10th (day 100) both to GALILEO and GPS. Time series denoted a similar behavior however there was an 11,69 mean TECU offset, 1,45 TECU standard deviation.
Global navigation satellite system (GNSS
) satellites emit signals that propagate as electromagnetic waves through space to the receivers which are located on or near the Earth’s surface or on other satellites. Thereby, electromagnetic waves travel through the ionosphere and the neutral atmosphere (troposphere) which causes signals to be delayed, damped, and refracted as the refractivity index of the propagation media is not equal to one. In this chapter, the nature and effects of GNSS signal propagation in both the troposphere and the ionosphere, aref examined. After a brief review of the fundamentals of electromagnetic waves their propagation in refractive media, the effects of the neutral atmosphere are discussed. In addition, empirical correction models as well as the state-of-the-art atmosphere delay estimation approaches are presented. Effects related to signal propagation through the ionosphere are dealt in a dedicated section by describing the error contribution of the first up to third-order terms in the refractive index and ray path bending. After discussing diffraction and scattering phenomena due to ionospheric irregularities, mitigation techniques for different types of applications are presented.
