scholarly journals Effect of TEC Variation on GPS Precise Point at Low Latitude

2009 ◽  
Vol 3 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Rajesh Tiwari ◽  
Soumi Bhattacharya ◽  
P.K. Purohit ◽  
A.K. Gwal
Keyword(s):  
Charged Particles ◽  
Rate Of Change ◽  
Ionospheric Irregularities ◽  
Electron Content ◽  
Positional Error ◽  
Gps Receiver ◽  
Equatorial Anomaly ◽  
Total Electron ◽  
Gps Receivers ◽  
Positioning Systems

The ionosphere is a dispersive medium of charged particles between the satellite and the user on Earth. These dispersive ionized media play a vital role in the various applications of GPS (Global Positioning Systems) because the ionosphere directly influences transionospheric radio waves propagating from the satellite to the receiver. Solar flares affect the ionization state of the ionosphere with their high intensity. Sometimes the intensity is so severe that it accelerates the rate of ionization, resulting in ionospheric storms; during the ionospheric storms the concentration of charged particles varies. Among the various phenomena in the ionosphere, TEC (Total Electron Content) is responsible for range error which produces a time delay in the radio signal. The rate of change of TEC with respect to time is abbreviated as ROT. It is one of the parameters that express the ionospheric irregularities with respect to time. This work investigates the effect of ROT fluctuation on the precise positioning of GPS receivers during low solar activity periods in the equatorial anomaly region. Good geometry and a sufficient number of locked satellites provide more accuracy within the centimeter level, but the case may be different when there are any ionospheric storms. Even a few satellite signals passing through the ionospheric irregularities can cause a significant error in positioning. Thus, it is important to understand the ionospheric irregularities observed by GPS receivers in order to correct them. The ROT (TEC/Minute) parameter is used here to study the occurrence of TEC fluctuation and its potential effect on GPS, such as a horizontal positional error or the satellite geometry of the GPS receiver. This investigation is based on the analysis of a one-year observation of a fixed GPS receiver installed at Bhopal (23.2020N, 77.4520E), India during low solar active period in 2005. The GPS receiver used here is a GISTM-based dual frequency NovAtel OEM4 GPS receiver.

scholarly journals Characteristics of ionospheric irregularities near the northern equatorial anomaly crest

2019 ◽  
Author(s):  
Jinghua Li ◽  
Guanyi Ma ◽  
Klemens Hocke ◽  
Qingtao Wan ◽  
Jiangtao Fan ◽  
...  
Keyword(s):  
Seasonal Variations ◽  
Ionospheric Irregularities ◽  
Lower Latitude ◽  
Occurrence Rate ◽  
Electron Content ◽  
Plasma Bubble ◽  
Equatorial Anomaly ◽  
Total Electron ◽  
Latitude Belt ◽  
Plasma Bubbles

Abstract. This paper detects the ionospheric irregularities with rate of total electron content (TEC) change index, ROTI from GPS observation at Taoyuan (24.95° N, 121.16° E) for the solar medium and minimum years of 2003 and 2008 in the declining phase of cycle 23, the solar maximum of 2014 in solar cycle 24. Local occurrence rate (LOR) is proposed to clarify the characteristics of the irregularities together with monthly occurrence rate (MOR) and ROTI maximum for 3 latitude belts, 20–23° N, 23–26° N, 26–29° N, around the equatorial anomaly crest. MOR in May/June is larger than those in equinoxes in 2008 and 2003, which is different from that of equatorial plasma bubbles. In 2014 although MOR maximum is observed in equinoxes, the MOR in May and June is much larger than that in September. Moreover, MORs in May to August at higher latitude belt 26–29° N are larger than those in lower latitude belts and smaller in the equinoxes. The latitudinal dependence of the LORs tends to be similar to that of MORs. Seasonal variations of LORs have a similar trend for different solar activities. Maximum LORs are observed in Feb/Mar and Sep/Oct, and moderate around June, which resemble those of plasma bubbles in seasonal variations, except for latitude belt 26–29° N where maximum LORs are seen in May–Jul. The seasonal variation of ROTI maximum conforms to that of the LOR. The results suggest that irregularities near the crest in May to August are mainly originated from nonequatorial process, which is more frequently happened but weaker than plasma bubble in both spatiotemporal scale and strength.

scholarly journals Spatial gradient of total electron content (TEC) between two nearby stations as indicator of occurrence of ionospheric irregularity

2018 ◽  
Author(s):  
Teshome Dugassa ◽  
John Bosco Habarulema ◽  
Melessew Nigussie
Keyword(s):  
Total Electron Content ◽  
Large Scale ◽  
Equatorial Region ◽  
Ionospheric Irregularity ◽  
Rate Of Change ◽  
Ionospheric Irregularities ◽  
Spatial Gradient ◽  
Electron Content ◽  
Total Electron ◽  
Pass Through

Abstract. The relation between the occurrence of ionospheric irregularity and spatial gradient of total electron content (TEC) during the post-sunset hours over the equatorial region is studied. The ionospheric irregularities could pose serious challenges to satellite-based navigation and positioning applications when trans-ionospheric signals pass through them. Different instruments and techniques have been applied to study the behavior of these ionospheric irregularities. In this study, the Global positioning system (GPS) based derived total electron content (TEC) was used to investigate the spatial gradient of TEC between two nearby stations as an indicator of the occurrence of ionospheric irregularity over the East African sector. The gradient of TEC between the two stations (ASAB: 4:34° N, 114:39° E and DEBK: 3:71° N, 109:34° E, geomagnetic) located within the equatorial region of Africa were considered in this study during the year 2014. The rate of change of TEC based derived index (ROTIave) is also used to observe the correlation between the spatial gradient of TEC and the occurrence of ionospheric irregularities. The result obtained shows that most of the maximum positive/depletions in the spatial gradient of TEC observed in March and September equinoxes are more pronounced between 19:00 LT–24:00 LT as the large-scale ionospheric irregularities do. Moreover, the observed spatial gradient of TEC shows two peaks (in March and September) and they exhibit equinoctial asymmetry where the March equinox is greater than September equinox. The enhancement in the spatial gradient of TEC and ROTIave during the 15 evening time period also show similar trends but lag 1–2 hrs from the equatorial electric field (EEF). The spatial gradient of TEC between the two nearby stations could be used as an indicator of the occurrence of ionospheric irregularities.

scholarly journals The Southern Hemisphere and equatorial region ionization response for a 22 September 1999 severe magnetic storm

2004 ◽  
Vol 22 (8) ◽  
pp. 2765-2773 ◽  
Author(s):  
E. Yizengaw ◽  
E. A. Essex ◽  
R. Birsa
Keyword(s):  
Magnetic Storm ◽  
Temporal Variations ◽  
Equatorial Region ◽  
Dominant Negative ◽  
Time Shift ◽  
Electron Content ◽  
Eastern Region ◽  
Equatorial Anomaly ◽  
Total Electron ◽  
Positioning Systems

Abstract. The ionospheric storm evolution process was monitored during the 22 September 1999 magnetic storm over the Australian eastern region, through measurements of the ionospheric Total Electron Content (TEC) from seven Global Positioning Systems (GPS) stations. The spatial and temporal variations of the ionosphere were analysed as a time series of TEC maps. Results of our analysis show that the main ionospheric effect of the storm under consideration are: the long lasting negative storm effect during a magnetic storm at mid-latitude regions; the strong, positive disturbances during the storm's main phase at auroral latitude regions; the effects of storm-induced equatorward directed wind causing a positive disturbance at high and mid-latitude stations with appropriate time shift between higher and lower latitudes; daytime poleward movement of depleted plasma that causes temporary suppression of the equatorial anomaly during the start of the storm recovery phase; and prompt penetration of eastward electric fields to ionospheric altitudes and the production of nearly simultaneous TEC enhancement at all latitudes. In general, we found dominant negative disturbance over mid and high latitudes and positive disturbance at low latitudes. A comparison of storm-time behaviour of TEC determined from GPS satellites, and foF2 derived from ionosondes at a range of latitudes, showed reasonable agreement between the two independent measurements.

scholarly journals Latitudinal extension of low-latitude scintillations measured with a network of GPS receivers

2004 ◽  
Vol 22 (9) ◽  
pp. 3155-3175 ◽  
Author(s):  
C. E. Valladares ◽  
J. Villalobos ◽  
R. Sheehan ◽  
M. P. Hagan
Keyword(s):  
Flux Tube ◽  
Magnetic Equator ◽  
Electron Content ◽  
Equatorial Anomaly ◽  
Density Profiles ◽  
Total Electron ◽  
Gps Receivers ◽  
F Region ◽  
Power Maps ◽  
Gps Scintillations

Abstract. A latitudinal-distributed network of GPS receivers has been operating within Colombia, Peru and Chile with sufficient latitudinal span to measure the absolute total electron content (TEC) at both crests of the equatorial anomaly. The network also provides the latitudinal extension of GPS scintillations and TEC depletions. The GPS-based information has been supplemented with density profiles collected with the Jicamarca digisonde and JULIA power maps to investigate the background conditions of the nighttime ionosphere that prevail during the formation and the persistence of plasma depletions. This paper presents case-study events in which the latitudinal extension of GPS scintillations, the maximum latitude of TEC depletion detections, and the altitude extension of radar plumes are correlated with the location and extension of the equatorial anomaly. Then it shows the combined statistics of GPS scintillations, TEC depletions, TEC latitudinal profiles, and bottomside density profiles collected between September 2001 and June 2002. It is demonstrated that multiple sights of TEC depletions from different stations can be used to estimate the drift of the background plasma, the tilt of the plasma plumes, and in some cases even the approximate time and location of the depletion onset. This study corroborates the fact that TEC depletions and radar plumes coincide with intense levels of GPS scintillations. Bottomside radar traces do not seem to be associated with GPS scintillations. It is demonstrated that scintillations/depletions can occur when the TEC latitude profiles are symmetric, asymmetric or highly asymmetric; this is during the absence of one crest. Comparison of the location of the northern crest of the equatorial anomaly and the maximum latitude of scintillations reveals that for 90% of the days, scintillations are confined within the boundaries of the 50% decay limit of the anomaly crests. The crests of the anomaly are the regions where the most intense GPS scintillations and the deepest TEC depletions are encountered. In accord with early results, we observe that GPS scintillations/TEC depletions mainly occur when the altitude of the magnetic equator F-region is above 500km. Nevertheless, in many instances GPS scintillations and TEC depletions are observed to exist when the F-layer is well below 500km or to persist when the F-layer undergoes its typical nighttime descent. Close inspection of the TEC profiles during scintillations/depletions events that occur when the equatorial F-layer peak is below 500km altitude reveals that on these occasions the ratio of the crest-to-equator TEC is above 2, and the crests are displaced 10° or more from the magnetic equator. When the equatorial F-layer is above 500km, neither of the two requirements is needed, as the flux tube seems to be inherently unstable. We discuss these findings in terms of the Rayleigh-Taylor instability (RTI) mechanism for flux-tube integrated quantities. We advance the idea that the seeming control that the reverse fountain effect exerts on inhibiting or suppressing GPS scintillations may be related to the redistribution of the density and plasma transport from the crests of the anomaly toward the equatorial region and then to much lower altitudes, and the simultaneous decrease of the F-region altitude. These two effects originate a decrease in the crest/trough ratio and a reduction of the crests separation, making the whole flux tube more stable to the RTI. The correspondence between crest separation, altitude of the equatorial F-region, the onset of depletions, and the altitude (latitude) extension of plumes (GPS scintillations) can be used to track the fate of the density structures.

scholarly journals Characterization of multi-scale ionospheric irregularities using ground-based and space-based GNSS observations

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
YuXiang Peng ◽  
Wayne A Scales ◽  
Michael D Hartinger ◽  
Zhonghua Xu ◽  
Shane Coyle
Keyword(s):  
Formation Flying ◽  
Satellite System ◽  
Ionospheric Irregularities ◽  
Mission Design ◽  
Electron Content ◽  
Total Electron ◽  
Spatial And Temporal Scales ◽  
Multi Scale ◽  
Global Navigation Satellite ◽  
Gnss Observations

AbstractIonospheric irregularities can adversely affect the performance of Global Navigation Satellite System (GNSS). However, this opens the possibility of using GNSS as an effective ionospheric remote sensing tool. Despite ionospheric monitoring has been undertaken for decades, these irregularities in multiple spatial and temporal scales are still not fully understood. This paper reviews Virginia Tech’s recent studies on multi-scale ionospheric irregularities using ground-based and space-based GNSS observations. First, the relevant background of ionospheric irregularities and their impact on GNSS signals is reviewed. Next, three topics of ground-based observations of ionospheric irregularities for which GNSS and other ground-based techniques are used simultaneously are reviewed. Both passive and active measurements in high-latitude regions are covered. Modelling and observations in mid-latitude regions are considered as well. Emphasis is placed on the increased capability of assessing the multi-scale nature of ionospheric irregularities using other traditional techniques (e.g., radar, magnetometer, high frequency receivers) as well as GNSS observations (e.g., Total-Electron-Content or TEC, scintillation). Besides ground-based observations, recent advances in GNSS space-based ionospheric measurements are briefly reviewed. Finally, a new space-based ionospheric observation technique using GNSS-based spacecraft formation flying and a differential TEC method is demonstrated using the newly developed Virginia Tech Formation Flying Testbed (VTFFTB). Based on multi-constellation multi-band GNSS, the VTFFTB has been developed into a hardware-in-the-loop simulation testbed with external high-fidelity global ionospheric model(s) for 3-satellite formation flying, which can potentially be used for new multi-scale ionospheric measurement mission design.

scholarly journals Characterization of ionospheric irregularities over Vietnam and adjacent region for the 2008-2018 period

2021 ◽  
Author(s):  
Dung Nguyen Thanh ◽  
Minh Le Huy ◽  
Christine Amory-Mazaudier ◽  
Rolland Fleury ◽  
Susumu Saito ◽  
...  
Keyword(s):  
Solar Activity ◽  
Correlation Coefficients ◽  
Rate Of Change ◽  
Occurrence Rate ◽  
High Solar Activity ◽  
Electron Content ◽  
Total Electron ◽  
Plasma Irregularities ◽  
Almost All ◽  
Continuous Gps

This paper presents the variations of the rate of change of Total Electron Content (TEC) index (ROTI), characterizing the occurrence of ionospheric plasma irregularities over Vietnam and neighboring countries in the Southeast Asian region using the continuous GPS data during the 2008-2018 period. The results showed that the occurrence of strong ROTI in all stations is maximum in equinox months March/April and September/October and depends on solar activity. The ROTI is weak during periods of low solar activity and strong during periods of high solar activity. There is an asymmetry between the two equinoxes. During maximum and declining phases of 2014-2016, occurrence rates in March equinox are larger than in September equinox, but during the descending period of 2010-2011, the occurrence rates in September equinox at almost all stations are larger than in March equinox. The correlation coefficients between the monthly occurrence rate of irregularities and the F10.7 solar index at the stations in the equatorward EIA crest region are higher than at those in the magnetic equatorial and the poleward EIA crest regions. The irregularity occurrence is high in the pre-midnight sector, maximum between 2000 LT to 2200 LT. The maximum irregularity occurrence is located around 4-5° degrees in latitude equator-ward away from the anomaly crests.

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