Determination Of Total Electron Content Research Articles

Determination of total electron content in the ionosphere over the territory of the Republic of Belarus based on global navigation satellite systems data

We present the results of experimental studies of electron content in the ionosphere over the territory of the Republic of Belarus based on data from global navigation satellite systems. The results of measurements of the precise positioning system of the Republic of Belarus and navigation data of GPS satellites in RINEX format were used as input data. Expressions for calculation of the total electron content using the two-frequency method and a combination of measurements by phase and code delays are given. Algorithms for eliminating cycle slip and determining differential code biases are used. Examples of calculating the vertical electron content over the Republic of Belarus at different moments of time are demonstrated. The obtained results are reasonable to use in monitoring of the ionosphere in order to provide reliable operation of radio systems, detection of ionospheric anomalies of natural and artificial origin, as well as forecasting of natural phenomena on their basis.

Doprinos određivanju jonosferskog kašnjenja GNSS satelitskih signala na teritoriji Republike Srbije

Multi-frequency GNSS satellite signals and their availability enable research in undifferentiated and uncombined models in which a single signal at each frequency is a corresponding independent observation. Such possibilities are reflected by the significant interest in geodetic research as well as in many areas of application of GNSS observation. On the geometric path of the signal between the satellite and the receiver, a significant source of GNSS measurement errors comes from the medium of propagation of electromagnetic waves. Errors attributed to signal propagation are ionospheric and tropospheric signal delay. The mentioned error sources significantly affect the quality of certain pseudorange and, thus, the quality of the receiver's position in the form of three-dimensional coordinates. This paper presents the analysis and determination of the ionospheric delay of GNSS satellite signals based on the determination of Total Electron Content - TEC at five stations (Beograd, Leskovac, Sombor, Zaječar, and Kraljevo) in the territory of the Republic of Serbia. In order to determine TEC values, the software called "GPS-TEC analysis" developed within the Institute for Scientific Research, Boston College, USA was used, which enables the determination of the TEC value on the path between the satellite and the receiver. The data collection was carried out within the year 2022 so that the measurement sessions include characteristic dates when the most significant fluctuations are expected in the context of seasonal variations.

S-system theory applied to array-based GNSS ionospheric sensing

The GPS carrier-phase and code data have proven to be valuable sources of measuring the Earth’s ionospheric total electron content (TEC). With the development of new GNSSs with multi frequency data, many more ionosphere-sensing combinations of different precision can be formed as input of ionospheric modelling. We present the general way of interpreting such combinations through an application of S-system theory and address how their precision propagates into that of the unbiased TEC solution. Presenting the data relevant to TEC determination, we propose the usage of an array of GNSS antennas to improve the TEC precision and to expedite the rather long observational time-span required for high-precision TEC determination.

Array-Aided Multifrequency GNSS Ionospheric Sensing: Estimability and Precision Analysis

The dual-frequency Global Positioning System has proven to be an effective means of measuring the Earth's ionosphere and its total electron content (TEC). With the advent of multifrequency signals from more Global Navigation Satellite Systems (GNSSs), the opportunity arises to construct many more ionosphere-sensing combinations of GNSS data. With such diversity, various estimable ionospheric delays with differing interpretations (and of different precision) can be formed. How such estimable ionospheric delays should be interpreted, and the extent to which they contribute to the precision with which the unbiased TEC can be estimated, are the topics of this paper. Based on multifrequency GNSS code-only, phase-only, and phase-and-code data, we derive the closed-form solutions of different types of ionospheric observables that each can serve as input of an externally provided ionospheric model for TEC determination. Within such a general least-squares framework, we generalize the widely used phase-to-code levelling technique to its multifrequency version. We also show that only certain specific linear combinations of the observables contribute to the TEC solutions. As a further improvement of the multifrequency GNSS-derived TEC solution, we propose and study the usage of an array of GNSS antennas. Analytical solutions, supported by numerical examples, of this array-based concept are presented, together with a discussion on its relevance for TEC determination. This concerns the roles of time averaging and time differencing, of integer ambiguity resolution, and of the number of frequencies and number of array antennas in determining TEC.

Validation of the GPS TEC maps with TOPEX data

The existence of a worldwide IGS (International GPS Service) permanent network of dual frequency receivers, makes feasible the computation of Global Ionospheric Maps (GIM's) of vertical Total Electron Content (TEC). The GIM's computed by the IGS Associate Analisys Centers (IAAC's) are being computed in a daily basis since 1998. The comparison with other kinds of forecast GIM's (computed from the International Reference Ionosphere (IRI) model and the GPS broadcast model) show that the GPS GIM's provide better accuracy and are useful for different applications such as navigation and time transfer. In this context, the performance of both kind of models are presented in this work in order to determine the accuracy of the different Global Ionospheric Maps. This is done by comparing with the TOPEX data that provides an indepentent and precise vertical TEC determination over the oceans (at the level of few TECU) which provides a way of validating the GIM's.

Performance of different TEC models to provide GPS ionospheric corrections

The existence of a worldwide international GPS service (IGS) permanent network of dual-frequency receivers makes the computation of global ionospheric maps (GIMs) of total electron content (TEC) feasible. The GIMs computed by the IGS Associate Analysis Centers on a daily basis and by other kinds of forecast GIMs, which can be computed from, for instance, the international reference ionosphere (IRI) model, and the GPS broadcast models in the navigation message, can be applied to a broad diversity of fields, for instance as, navigation and time transfer. In this context, the performance of different kinds of models are presented in order to determine the accuracy of the different GIM. This is carried out by comparison with the TOPEX data that provides an independent and precise (at the level of few TECU) vertical TEC determination over the oceans and seas. Thus, the obtained accuracies, in terms of global relative error, ranging from 54% corresponding to the GPS broadcast model, to about 41% corresponding to IRI climatological model, and to less than 30% corresponding to GPS data driven models.

The protonospheric contribution to GPS total electron content: Two‐station measurements

Results are presented from an experiment to estimate the contribution of plasma on ray paths through the protonosphere to measurements of total electron content (TEC) using Global Positioning System (GPS) signals. Simulations using the Sheffield University plasmasphere ionosphere model show that observations of GPS satellites made at two stations separated by a few degrees of latitude could involve a common ionospheric volume but very different intersection geometries of the ray paths with protonospheric flux tubes. Experimental results demonstrate that, on average, higher equivalent vertical TECs are measured on ray paths to the south than those to the north of the European midlatitude stations considered here. The observations are discussed in terms of the known asymmetries of the protonospheric flux tubes, and caution is advised in the use of thin‐shell ionospheric models for precise determination of TEC or correction for its effects on GPS systems.

The effect of the protonosphere on the estimation of GPS total electron content: Validation using model simulations

Simulated observations of total electron content (TEC) along ray paths from Global Positioning System (GPS) satellites have been used to validate the estimation of TEC using GPS measurements. The Sheffield University plasmasphere ionosphere model (SUPIM) has been used to create electron densities that were integrated along ray paths from actual configurations of the GPS constellation. The resultant slant electron contents were then used as inputs to validate the self‐calibration of pseudo‐range errors (SCORE) process for the determination of TEC from GPS observations. It is shown that if the plasma resides only in the ionosphere below 1100 km, then the SCORE procedure determines the TEC to a high degree of accuracy. When the contribution of the electrons in the protonosphere above 1100 km is included, the analysis results in TEC estimates that are high by some 2 TEC units (TECU) for conditions appropriate to European midlatitudes at solar minimum. However, if a restriction is placed in the analysis on use of observations equatorward of the station, then allowance can be made for the effect of the protonosphere. It is shown that with appropriate selection of the boundary for the observations, TEC can be estimated by SCORE to better than 1 TECU for the conditions of the simulation. Sample results are included from actual experimental observations using GPS to demonstrate the effect of compensation for the protonospheric plasma.

Relationships between GPS-signal propagation errors and EISCAT observations

Abstract. When travelling through the ionosphere the signals of space-based radio navigation systems such as the Global Positioning System (GPS) are subject to modifications in amplitude, phase and polarization. In particular, phase changes due to refraction lead to propagation errors of up to 50 m for single-frequency GPS users. If both the L1 and the L2 frequencies transmitted by the GPS satellites are measured, first-order range error contributions of the ionosphere can be determined and removed by difference methods. The ionospheric contribution is proportional to the total electron content (TEC) along the ray path between satellite and receiver. Using about ten European GPS receiving stations of the International GPS Service for Geodynamics (IGS), the TEC over Europe is estimated within the geographic ranges -20°≤ λ ≤40°E and 32.5°≤ Φ ≤70°N in longitude and latitude, respectively. The derived TEC maps over Europe contribute to the study of horizontal coupling and transport proces- ses during significant ionospheric events. Due to their comprehensive information about the high-latitude ionosphere, EISCAT observations may help to study the influence of ionospheric phenomena upon propagation errors in GPS navigation systems. Since there are still some accuracy limiting problems to be solved in TEC determination using GPS, data comparison of TEC with vertical electron density profiles derived from EISCAT observations is valuable to enhance the accuracy of propagation-error estimations. This is evident both for absolute TEC calibration as well as for the conversion of ray-path-related observations to vertical TEC. The combination of EISCAT data and GPS-derived TEC data enables a better understanding of large-scale ionospheric processes.

Total electron content obtained from ionogram data alone

A method to obtain the total electron content (TEC) of the ionosphere over Tucumán (26.9° S; 65.4° W), from ionogram data alone, is reported. To accomplish this, two Chapman profile expressions for the electron density (n) distribution in the F region are assumed, and a characteristic point of the n profile, called F region base point, is required. This method allows the TEC for a given particular time (not average) to be obtained. The results suggest that it could be a new method to calibrate polarimeter records used to measure TEC, and it could also allow the determination of TEC at predawn hours where only ionosounder data are available.

Comparative ionospheric and plasmaspheric electron contents from three world regions

THE radio beacon experiment1–3 aboard the geostationary Applied Technology Satellite ATS-6 enables the determination of total electron content (TEC) to be made by two independent methods. The first—the Faraday polarisation rotation technique—has been widely used in obtaining TEC data. Faraday rotation is dependent on the Earth's magnetic field, and, since its magnitude is heavily weighted near the Earth, it is considered to provide integrated electron content values for altitudes below ∼1,500 km. The second—the dispersive-group-delay technique, in which the phase of the modulation envelope between a carrier and its sideband is compared at two frequencies—is independent of the Earth's magnetic field and thus yields the integrated electron content between the observer and the satellite signal source. The Faraday content, NF, and the dispersive-group-delay content, NT, therefore, yield the TEC up to ∼1,500 km and geostationary altitudes, respectively. The difference between NT and NF yields the content above ∼1,500 km, which is referred to as the plasmaspheric content, Np.

Determination of total electron content from differential Doppler records

Several existing and new methods of determining total electron content ( I) from differential Doppler records obtained from orbiting satellites are examined. The relative accuracy of different methods is compared through simulated and actual examples. It is found that though in case of no- or linear gradients all the methods give same results, only the method based on minimum curvature of I( t) curves is reliable in general case.

Determination of electron content at a low-latitude station with off-zenith transverse point

The importance of the choice of mean ionospheric height (hM) in the determination of latitude variation of total electron content (TEC) from satellite transmissions at a low-latitude station is investigated. By considering the concept of magneto-ionic mode coupling in the vicinity of the transverse region, the Faraday rotation as a function of latitude for a frequency of 40 MHz has been theoretically computed for Calcutta (12°N geomagnetic) by using typical electron concentration profiles representing different ionospheric conditions. This result was used to determine the criterion for the proper choice of hM consistent with least error in the determination of TEC over the entire latitude range of interest. It is found that the correct choice corresponds to the height of the transverse point at that latitude (TP) for which the Faraday rotation is a minimum. An incorrect choice of this height leads to substantial error in the computed electron content at latitudes to the north of TP, the error being as large as 3% per 10 km deviation from the best choice of hM. A method of deriving the correct choice of hM from actual Faraday rotation records is indicated.

Reply [to “Discussion of paper by F. L. Scarf, ‘Effect of coherent density fluctuations on the radar determination of total electron content’”

Journal of Geophysical Research (1896-1977)Volume 72, Issue 17 p. 4598-4601 Letters Reply [to “Discussion of paper by F. L. Scarf, ‘Effect of coherent density fluctuations on the radar determination of total electron content’”] Frederick L. Scarf, Frederick L. ScarfSearch for more papers by this author Frederick L. Scarf, Frederick L. ScarfSearch for more papers by this author First published: 1 September 1967 https://doi.org/10.1029/JZ072i017p04598AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume72, Issue171 September 1967Pages 4598-4601 RelatedInformation

Discussion of paper by F. L. Scarf, ‘Effect of coherent density fluctuations on the radar determination of total electron content’

Howard et al. [1965] and Yoh et al. [1966] have recently reported on a beautiful set of radar experiments in which group and phase delay introduced by the cislunar medium were interpreted in terms of a mean plasma electron concentration. Electron concentrations found by these techniques appear to be very much higher than those derived by other means, such as from whistlers [Carpenter, 1966], from micropulsations [Watanabe, 1965], or on theoretical grounds [Dessler and Michel, 1966]. Scarf [1966] subsequently attempted to explain the discrepancy as an effect of coherent density fluctuation on the mean propagation constants of the plasma, In what follows we show that the effect discussed by Scarf is probably unimportant and hence that some other explanation of the curious discrepancy between the results of the radar propagation experiments and the currently accepted model of the magnetospheric tail must be sought.

Effect of coherent density fluctuations on the radar determination of total electron content

Density fluctuation effect on radar determination of total electron content in terms of recent cislunar density measurement