Study Of Ionospheric Scintillation Research Articles

Systematic study of ionospheric scintillation over the indian low-latitudes during low solar activity conditions

A systematic study of ionospheric scintillation at the low-latitudes, especially around the Equatorial Ionization Anomaly (EIA) and the magnetic equator, is essential in understanding the dynamics of ionospheric variation and related physical processes. Our study involves NavIC S4C observations over Indore and Hyderabad. Additionally, GPS S4C observations over Indore were analyzed, under disturbed as well as quiet time ionospheric conditions from September 2017 through 2019, falling in the declining phase of the solar cycle 24. The S4C observations were further analyzed using proxy parameters: ROT and ROTI. These results have been obtained from three satellites of the NavIC constellation (PRNs 2, 5, and 6). The onset times of scintillations were observed to be around 19:30 LT (h) and 20:30 LT (h) for Hyderabad and Indore respectively, while the S4C peak values occurred between 22:00 LT (h) and 23:00 LT (h). The reliability of NavIC was evaluated using scattering coefficients that revealed a good correlation across the pair of signals during quiet time ionospheric conditions. The observations clearly show that the amplitude scintillation of the NavIC signal follows the Nakagami-m distribution along with the α-μ distribution as a depiction of the deep power fades caused by scintillation on these signals. This paper shows the impact of such systematic studies near these locations for the first time, in improving the understanding of the dynamic nature of low-latitude ionosphere under low solar activity conditions.

Study of ionospheric scintillation during geomagnetic storms at equatorial anomaly region Bhopal

GPS L-band signals get affected by ionospheric scintillation; as a result, satellite navigation too gets affected. The most extreme scintillation activity is expected to occur near the equatorial region during geomagnetic storms. The behavior and morphology of low-latitude ionosphere are different from the other latitudes. The space weather conditions in low latitude show different nature because of the geomagnetic field. Due to penetration of soft, high energetic particles, the plasma density increases, which is the main source of generation of ionospheric irregularities scintillation. GPS scintillation at low latitudes is primarily associated with equatorial spread F. Equatorial spread F is caused by ionospheric irregularities with a spatial spectrum extending from 100 km to less than 1 m. When GPS signals encounter the ionospheric irregularities of various sizes produced during high geomagnetic and solar activity, they undergo drastic changes in their phase and amplitude scintillation indices. The accuracy and reliability of GPS system get affected by scintillation. Also the atmosphere air molecule’s content and deviation of electrons, protons, neutrons according to flow rate are observed. In the present paper, we have studied the scintillation activity at low-latitude station Bhopal.

Amplitude scintillation index derived from C/N0 measurements released by common geodetic GNSS receivers operating at 1 Hz

Two widely used scintillation indexes $$ S_{4} $$ and $$ \sigma_{\varphi } $$ are generated by dedicated ionospheric scintillation monitoring receivers (ISMRs), which typically have 50-Hz temporal resolution and thus require substantial memory capabilities. Taking into consideration the huge number of common Global Navigation Satellite System (GNSS) receivers, the derivation of a GNSS receiver-based scintillation index as a supplement to the ISMR indexes is expected to improve the study of ionospheric scintillation. We developed an amplitude scintillation index, $$ S_{{4{\text{c}}}} $$, which is derived from the carrier-to-noise density ratio ($$ C/N_{0} $$) data released by common geodetic GNSS receivers operating at 1-Hz. The reliability of the $$ S_{{4{\text{c}}}} $$ index is compared with the typical scintillation index $$ S_{4} $$ of three ISMRs located in Hong Kong and Brazil. The statistics indicate that during scintillation activity, the correlation coefficient between $$ S_{{4{\text{c}}}} $$ (derived from common receivers) and $$ S_{4} $$ (generated by ISMRs) is generally higher than 0.9. The reliability of $$ S_{{4{\text{c}}}} $$ was also verified based on 1-year observations from two adjacent stations in Hong Kong, which are equipped with Leica GR50 and Septentrio PolaRxS Pro receivers, respectively. Long-term scintillation occurrence ($$ S_{{4{\text{c}}}} $$ > 0.2 vs. $$ S_{4} $$ > 0.2) rates show good agreement between $$ S_{{4{\text{c}}}} $$ and $$ S_{4} $$. In addition, two-dimensional $$ S_{{4{\text{c}}}} $$ maps (1° × 1°) generated by GPS L1 and BDS B1 signals data collected at 117 continuous operation tracking stations in China clearly show post-sunset super plasma bubbles as the source of ionospheric scintillation during the main phase of the intense storm that occurred on September 8, 2017. These results demonstrate the feasibility of using the $$ S_{{4{\text{c}}}} $$ index derived from the large volume of GNSS observations recorded by non-scintillation GNSS receivers for the study and monitoring of ionospheric scintillation.

S 4 index: Does it only measure ionospheric scintillation?

The study of ionospheric scintillation has played a critical role in ionospheric research and also in satellite positioning. This is due to the growing influence of GNSS in navigation and remote sensing activities and also because the scintillation severely degrades the performance of this system. The main parameter that has been used to investigate the ionospheric scintillation impact on quality of GNSS satellite signals is the S 4 index. However, we show that other effects such as multipath may mask the scintillation effects. Furthermore, we propose a method to separate the effect of multipath from scintillation in the S 4 index by a non-decimated wavelet multiscale decomposition, which is shift invariant and more appropriate to use in the analysis of time series. The results show that the multipath effect is evident in the smoother scales of multiscale decomposition by wavelet in the weak scintillation period. Once identified and estimated, this effect can be removed from the S 4 index series during strong scintillation periods and it becomes not significant in the scintillation S 4 index wavelet analysis. Investigations using data from different stations and satellites demonstrate that the effect of ionospheric scintillation varies with station location and elevation angle of the satellite. Therefore, each case must be treated individually.

A comparative study of GPS ionospheric scintillations and ionogram spread F over Sanya

Abstract. We analyze the data recorded during December 2011–November 2012 by a digital ionosonde and a GPS (Global Positioning System) scintillation and (total electron content) TEC receiver collocated at Sanya (109.6° E, 18.3° N; dip lat. 12.8° N), a low-latitude station in the Chinese longitude sector, to carry out a comparative study of ionospheric scintillations and spread F. A good consistency between the temporal variations of GPS scintillation (represented by the S4 index) and of ionogram spread F (represented by the QF index) is found in the pre-midnight period during equinox. However in the post-midnight period during equinox and in the period from post-sunset to pre-sunrise during June solstice, moderate spread F is seen without concurrent GPS scintillation. The possible cause responsible for the difference between post-midnight GPS scintillation and spread F during equinox could be due to the decaying of 400 m scale irregularities associated with equatorial spread F. Regarding the irregularities producing moderate QF and low S4 indices during June solstice, we suggest that the frequently observed sporadic E (Es) layer and the medium-scale traveling ionospheric disturbances (MSTIDs) over Sanya could play important roles in triggering the June solstitial spread-F events.

Initial GPS scintillation results from CASES receiver at South Pole, Antarctica

Connected Autonomous Space Environment Sensor (CASES) Global Positioning System (GPS) software‐defined receivers developed for ionospheric scintillation studies have been deployed on Autonomous Adaptive Low‐Power Instrument Platforms (AAL‐PIP) at South Pole, Antarctica. In this paper, we describe the AAL‐PIP experimental setup focusing on CASES. We explain in detail the method developed for analyzing CASES data, and report initial AAL‐PIP CASES results. Furthermore, we compare the CASES measurements with those from a modified Novatel GSV4004 GPS Ionospheric Scintillations and TEC Monitor (GISTM) receiver at the South Pole. CASES receivers have been successfully deployed and reliably operated in equatorial and midlatitude regions. Four of these GPS receivers, for the first time, are deployed in high‐latitude regions as a part of the National Science Foundation (NSF) funded project of deploying space science instrument platforms, AAL‐PIPs, in Antarctica since December 2010–2011. We present initial scintillation results recorded by a CASES receiver at South Pole during the storm on 24 January 2012 along with AAL‐PIP magnetometer observations. We have deduced that the CASES receiver scintillation observations agree with those from the Novatel GPS scintillation receiver. Since this is the first time a CASES receiver has been deployed to operate in a high latitude, low temperature, and low humidity environment, we consider this comparison a demonstration of its reliable operation as a science‐grade scintillation receiver in such conditions. We plan to study high latitude ionospheric irregularities by using observations from CASES and other ancillary instruments from Antarctica coupled with physical parameters derived from models.

Analysis of the Characteristics of Low-Latitude GPS Amplitude Scintillation Measured During Solar Maximum Conditions and Implications for Receiver Performance

Ionospheric scintillations are fluctuations in the phase and/or amplitude of trans-ionospheric radio signals caused by electron density irregularities in the ionosphere. A better understanding of the scintillation pattern is important to make a better assessment of GPS receiver performance, for instance. Additionally, scintillation can be used as a tool for remote sensing of ionospheric irregularities. Therefore, the study of ionospheric scintillation has both scientific as well as technological implications. In the past few years, there has been a significant advance in the methods for analysis of scintillation and in our understanding of the impact of scintillation on GPS receiver performance. In this work, we revisit some of the existing methods of analysis of scintillation, propose an alternative approach, and apply these techniques in a comprehensive study of the characteristics of amplitude scintillation. This comprehensive study made use of 32 days of high-rate (50 Hz) measurements made by a GPS-based scintillation monitor located in Sao Jose dos Campos, Brazil (23.2°S, 45.9°W, −17.5° dip latitude) near the Equatorial Anomaly during high solar flux conditions. The variability of the decorrelation time (τ0) of scintillation patterns is presented as a function of scintillation severity index (S4). We found that the values of τ0 tend to decrease with the increase of S4, confirming the results of previous studies. In addition, we found that, at least for the measurements made during this campaign, averaged values of τ0 (for fixed S4 index values) did not vary much as a function of local time. Our results also indicate a significant impact of τ0 in the GPS carrier loop performance for S4 ≥ 0.7. An alternative way to compute the probability of cycle slip that takes into account the fading duration time is also presented. The results of this approach show a 38% probability of cycle slips during strong scintillation scenarios (S4 close to 1 and τ0 near 0.2 s). Finally, we present results of an analysis of the individual amplitude fades observed in our set of measurements. This analysis suggests that users operating GPS receivers with C/N0 thresholds around 30 dB-Hz and above can be affected significantly by low-latitude scintillation.

Observations of the power cosmic radio sources on the radio telescope URAN-4 during 1998–2004

To investigate the variability of the flux density, observations of four power radio sources (3C144, 3C274, 3C405 and 3C461) were carried out on the radio telescope URAN-4 at two frequencies, 20 and 25 MHz, during 1998–2005. The automatic procedure for obtaining the observations is considered briefly in this paper. The results of previous procedures are presented in the tables. They contained information that allows the vast amount of material that has been gathered to be analysed in more detail as follows: estimation of the source flux densities, study of ionospheric scintillations, investigation of the dependence of the direction pattern on the hour angle and the solving of other tasks. The dependence of the URAN-4 direction pattern on the hour angle is cited as an example of the mean procedure using many observation data. Long-time observation series allowed the cycle year dependence of the ionospheric scintillation index to be obtained.

Multifrequency study of ionospheric scintillation at Ascension Island

Multifrequency amplitude scintillation data at L and C bands from the equatorial region at Ascension Island are used to study the spectral index n for the scintillation index S4. The average frequency dependence of the scintillation index (S4) is found to be f−1.68. It is shown that the spectral index tends to be larger for events which occur after 2030 local time than for events which occur before 2030. This may indicate temporal evolution of the irregularity spectrum. Model studies based on a two component power law irregularity spectrum are applied to relate changes in n to spectral evolution and to show that the observations are consistent with recent in situ measurements. Possible geophysical implications are also discussed.

Radio wave scintillations in the ionosphere

The phenomenon of scintillation of radio waves propagating through the ionosphere is reviewed in this paper. The emphasis is on propagational aspects, including both theoretical and experimental results. The review opens with a discussion of the motivation for stochastic formulation of the problem. Based on measurements from in-situ, radar, and propagation experiments, ionospheric irregularities ate found to be characterized, in general, by a power-law spectrum. While earlier measurements indicated a spectral index of about 4, there is recent evidence showing that the index may vary with the strength of the irregularity and possibly a two-component spectrum may exist with different spectral indices for large and small structures. Several scintillation theories including the Phase Screen, Rytov, and Parabolic Equation Method (PEM) are discussed next. Statistical parameters of the signal such as the average signal, scintillation index, rms phase fluctuations, correlation functions, power spectra, distributions, etc., are investigated. Effects of multiple scattering are discussed. Experimental results concerning irregularity structures and signal statics are presented. These results are compared with theoretical predictions. The agreements are shown to be satisfactory in a large measure. Next, the temporal behavior of a transionospheric radio signal is studied in terms of a two-frequency mutual coherence function and the temporal moments. Results including numerical simulations are discussed. Finally, some future efforts in ionospheric scintillation studies in the areas of transionospheric communication and space- and geophysics are recommended.

A study of ionospheric scintillations of phase and quadrature components

Statistical properties of the phase as well as the quadrature components of the ionospheric scintillating radio signal are investigated using data received from the ATS 6 radio beacon experiment. For weak scintillation the phase‐quadrature components dominate the fluctuations. When the scintillation level is increased, the multiple scattering seems to have the effect of equalizing the power between the two quadrature components. The phase spectra are consistent with power law irregularity models. For strong scintillations the phase spectra become flattened. The spectra for the quadrature components as well as the frequency dependence of the mean square phase fluctuations are studied. The experimental data were interpreted using existing scintillation theories.