Amplitude Scintillation Research Articles

A measure of ionospheric irregularities: zonal velocity and its implications for L-band scintillation at low-latitudes

We estimate the zonal drift velocity of small-scale ionospheric irregularities at low latitude by leveraging the spaced-receivers technique applied to two GNSS receivers for scintillation monitoring installed along the magnetic parallel passing in Presidente Prudente (Brazil, magnetic latitude 12.8°S). The investigated ionospheric sector is ideal to study small-scale irregularities, being located close to the expected position of the southern crest of the equatorial ionospheric anomaly. The measurement campaign took place between September 2013 and February 2014, i.e. equinox and summer solstice seasons under solar maximum, during which the probability of formation of small-scale irregularities is expected to maximize. We found that the hourly average of the velocity increases up to 135 m/s right after the local sunset at ionospheric altitudes and then smoothly decreases in the next hours. Such measurements are in agreement with independent estimations of the velocity made by the Incoherent Scatter Radar located at the Jicamarca Radio Observatory (magnetic latitude 0.1°N), by the Boa Vista Ionosonde (magnetic latitude 12.0°N), and by applying a recently-developed empirical regional short-term forecasting model. Additionally, we investigated the relationship with the percentage occurrence of amplitude scintillation; we report that it is exponentially dependent on the zonal velocity of the irregularities that cause it.

Daytime GNSS scintillation due to Es over Arabian Peninsula during low solar activity

A constant presence of daytime GNSS phase (σϕ) and amplitude (S4) scintillation during the times sporadic-E (Es) was observed, is reported. The most favorable local time (LT) of the day for the occurrences are the morning (08:00 to 12:00) and the late afternoon (16:00 to 18:00) hours. Es and σϕ/S4 are found to be in very good correlation. Low occurrences of post-sunset scintillation suggest that the main driver of the ionospheric scintillation over Arabian Peninsula during the low solar activity period is the presence of Es.

Development and performance evaluation of tropospheric scintillation model on Ku-band satellite link over Akure, Nigeria

Existing amplitude scintillation prediction models often perform less satisfactorily when deployed outside the regions where they were formulated. This necessitates the need to evaluate the performance of scintillation models developed in one region using data data from other regions while documenting their relative errors. Due to its variation with elevation angle, frequency, other link parameters and meteorological factors, we employed three years (January 2016 to December 2018) of concurrently measured satellite radio beacons and tropospheric weather parameters to develop a location-based amplitude scintillation prediction model over the Earth-space path of Akure (7.17oN, 5.18oE), South-western Nigeria. The satellite beacon measurement used Tektronix Y400 NetTek Analyzer at 1 s integration time while meteorological parameters, namely; temperature, pressure and relative humidity were measured using Davis Vantage Vue weather station at 1 min integration time. Comparative study of the model’s performance with nine (9) existing scintillation prediction models indicates that the best and worst performing models, in terms of root mean square error (RMSE), are the Statistical Temperature and Refractivity (STN) and direct physical and statistical prediction (DPSP) models with values 11.48 and 51.03 respectively. Also, worst month analysis indicates that April, with respective enhancement and fade values of 0.88 and 0.90 dB for 0.01% exceedance, is the overall worst calendar month for amplitude scintillation.

Carrier frequency disturbance distributions on GPS during equatorial ionospheric scintillation

In the equatorial region, deep amplitude fading in global positioning system (GPS) signals frequently occurs during the strong ionospheric scintillation, it can lead to the loss of lock in GPS carrier tracking loops, and result in increased positioning error and even navigation interruption. The relationships between amplitude scintillation indices and detrended carrier frequency are investigated, based on GPS L1 C/A signals during the last peak of the solar cycle at the low latitude site of São José dos Campos, Brazil (23.2S, 45.9W) from 2013 to 2015. Corresponding mathematic model of the probability distribution function is built for the first time to provide statistical analysis on the above relationships. The results show that the standard carrier frequencies reveal an almost linear relation with the amplitude scintillation indices. Moreover, the frequency widths of de-trended frequency are proportional to levels of amplitude scintillation when the value of the peak probability is lower than the corresponding boundary. A conclusion can be drawn that different levels of amplitude scintillation will influence the fluctuation of the carrier frequency. The analysis will provide useful guidance to set the receiver's bandwidth with respect to the different scintillation levels and design the advanced tracking algorithms to improve the robustness and precision of the GPS receiver.

Space Diversity Mitigation Effects on Ionospheric Amplitude Scintillation With Basis on the Analysis of C/NOFS Planar Langmuir Probe Data

AbstractThe present contribution applies a modified version of a well‐known weak‐scatter scintillation model to the propagation paths between an Earth station and two geostationary satellites, as they are affected by drifting ionospheric irregularities detected by the planar Langmuir probe onboard the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. This study considers one year of data from a limited altitude range, two longitude sectors and frequencies to analyze the mitigation effects from the angular distance between the geostationary satellites on the space diversity gain, considering the statistical distributions of the amplitude scintillation index S4. The results indicate that the space diversity gain increases with the angular distance between geostationary satellites. However, once the angular distance between the geostationary satellites reaches a certain limit (approximately 20°), the space diversity gain no longer increases. Additionally, these gains are high at the L1 frequency and less impressive at an Ultra High Frequency (UHF). It is shown that these observations are consistent with the South American and Indian‐Asian equatorial and low‐latitude ionospheric environments, also characterized through the same data and the scintillation formulation.

Leveraging Geodetic GPS Receivers for Ionospheric Scintillation Science

AbstractWe demonstrate scintillation analysis from a network of geodetic Global Positioning System (GPS) receivers which provide data at 1‐second resolution. We introduce proxy phase (σTEC) and amplitude (SNR4) scintillation indices and validate them against the rate of change of TEC index (ROTI) and S4. Additionally, we validate scintillation observations against a Connected Autonomous Space Environment Sensor scintillation receiver. We develop receiver‐dependent scintillation event thresholding using hardware‐dependent noise variance. We analyze 6 days adjacent to the 7–8 September 2017 geomagnetic storm, using 169 receivers covering magnetic latitudes between 15° and 65° in the American longitude sector. We leverage the available spatial sampling coverage to construct 2‐D maps of scintillation and present episodic evolution of scintillation intensifications during the storm. We show that low‐latitude and high‐latitude scintillation morphology match well‐established scintillation climatology patterns. At midlatitudes, spatiotemporal evolution of scintillation partially agrees with known scintillation patterns. Additionally, the results reveal previously undocumented midlatitude scintillation‐producing structures. The results provide an unprecedented view into the spatiotemporal development of scintillation‐producing plasma irregularities and provide a resource to further exploit scintillation evolution at large spatial scales.

An analysis of global ionospheric disturbances and scintillations during the strong magnetic storm in September 2017

Severe space weather events, e.g., solar flares and magnetic storm, can cause significant disturbances to the global ionosphere. The radio frequency signals, such as wireless communications and global satellite navigation system (GNSS) signals, often experience strong scintillations when traveling through the disturbed ionosphere layer. On 6 September 2017, the sun emitted the largest solar flare classified X9.3 since the 24th solar activity week. It triggered the geomagnetic storm and ionospheric storm on September 8, causing severe disturbances and scintillations of ionospheric. In this work, we take this event as the objective to investigate the characteristics of the ionosphere disturbance. First, the temporal and spatial distributions of ionospheric total electron content (TEC) are analyzed using the ground-based IGS data. The change of TEC is highly correlated with that of the geomagnetic indices and the magnetic storm has the greatest impact on low latitudes. Then, a five-point moving average method is adopted to extract the spatial fluctuations based on post-processed electron density and TEC data from COSMIC and GRACE missions. We find they show different disturbance characteristics in spatial distribution. In addition, the GNSS amplitude scintillation index S4 which is available from the COSMIC satellite mission is used to characterize ionospheric scintillation during this event. Weak scintillation occurred in most parts of the world on September 8 2017, while moderate scintillation is mainly concentrated around 120° W and 100° E. Our study can provide a basis for better evaluating the impact of ionosphere disturbance changes on satellite communication and navigation in space weather events.

Ionospheric irregularities and scintillations: a direct comparison of in situ density observations with ground-based L-band receivers

Ionospheric irregularities can affect satellite communication and navigation by causing scintillations of radio signals. The scintillations are routinely measured using ground-based networks of receivers. This study presents observations of ionospheric irregularities by Langmuir probes on the Swarm satellites. They are compared with amplitude scintillation events recorded by the Global Positioning System-Scintillation Network and Decision Aid (GPS-SCINDA) receiver installed in Mbarara (Lat: 0.6^{circ }hbox {S}, Lon: 30.8^{circ }hbox {E} , Mag. lat: 10.2^{circ }hbox {S}). The study covers the years from 2014 to 2018 when both data sets were available. It was found that the ground-based amplitude scintillations were enhanced when Swarm registered ionospheric irregularities for a large number of passes. The number of matching observations was greater for Swarm A and C which orbited at lower altitudes compared to Swarm B. However, some counterexamples, i.e., cases when in situ electron density fluctuations were not associated with any observed L-band amplitude scintillation and vice versa, were also found. Therefore, mismatches between observed irregularity structures and scintillations can occur just over a few minutes and within distances of a few tens of kilometers. The amplitude scintillation strength, characterized by the S4 index was estimated from the electron density data using the well-known phase screen model for weak scattering. The derived amplitude scintillation was on average lower for Swarm B than for A and C and less in accordance with the observed range. Irregularities at an altitude of about 450 km contribute strongly to scintillations in the L-band, while irregularities at about 510-km altitude contribute significantly less. We infer that in situ density fluctuations observed on passes over or near Mbarara may be used to indicate the risk that ionospheric radio wave scintillations occur at that site.

GPS derived amplitude scintillation proxy model: A case over a low latitude station in East Africa

Ionospheric scintillation is quite a common phenomenon over the low latitude regions and in East Africa it is often monitored using measurements from the SCIntillation Network Decision Aid (SCINDA) receivers. The SCINDA receivers over East Africa are characterized by long base lines and data paucity thus offering a huge challenge in the long term scintillation characterization over the region. To alleviate this challenge, we implemented the use of data from the dual frequency GPS receivers of the IGS network in combination with data from the SCINDA receiver at Nairobi, Kenya to model amplitude scintillation. The data from the SCINDA (geographic coordinates 36.808oE, −1.274oN) and GPS (geographic coordinates 36.893oE, −1.221oN) receivers were used to derive S4 index and its proxy respectively. Comparison of the S4 and its proxy revealed a high correlation coefficient between the two datasets. Scintillation occurrence was observed to peak during the equinox months of March–April and September–October. The vernal equinox was observed to have less frequent scintillation events than the autumnal equinox. The local time (LT) scintillation occurrence shows a peak between 20:00 LT and 23:00 LT. An empirical hybrid amplitude scintillation occurrence probability model was then developed. The results show that the model predicted values were in good agreement with the observed amplitude scintillation occurrence probabilities from the SCINDA receiver. This observation suggests that the model is a useful tool for approximating amplitude scintillation occurrence probabilities at L-band frequencies at African equatorial latitudes.

Characteristics of Ionospheric Irregularities Using GNSS Scintillation Indices Measured at Jang Bogo Station, Antarctica (74.62°S, 164.22°E)

AbstractGlobal Navigation Satellite System (GNSS) signals strongly depend on the ionospheric conditions, which are composed of electrons and ions generated by solar radiation and particle precipitation. Ionospheric plasma irregularities may cause the scintillation of the GNSS signals or even the loss of signal lock, resulting in the reduction of positioning accuracy and timing precision. Phase scintillation phenomenon is known to occur frequently at high latitudes and primarily related to a significant plasma density gradient, which is due to fast plasma flows in the polar region, energetic particle precipitation in the auroral region, polar cap patches, or several instability mechanisms. Statistical studies are required to understand the characteristics of ionospheric (both phase and amplitude) scintillations at high latitudes. Here, we report the results of ionospheric scintillation measurements at Jang Bogo Station (JBS; 74.62°S, 164.22°E), located inside the polar cap region in Antarctica. The occurrence rates of ionospheric scintillations over the JBS are recorded for 2 years (2017–2018) during solar minimum conditions. The occurrence rates of amplitude scintillations increase only at lower elevation angles (below 30°), which are hard to determine whether the source is ionospheric irregularity or ambient noise such as multipath. In contrast, the occurrence rates of phase scintillations depend on the azimuth angle, season, magnetic activity, magnetic local time, and signal frequency. The results of our analysis suggest that users of the GNSS should consider these parameters to prepare for the degradation of the GNSS performance at high latitudes in the Southern Hemisphere.

L-Band Amplitude Scintillations During Solar Maximum at a Low Latitude Station

The Global Positioning System (GPS) is one of the most important and useful technologies developed for information and communication technology. Propagated wireless signals along the GPS link are affected by the ionospheric irregularities, therefore the GPS signals may experience ionospheric scintillation. In this study, GPS L-band amplitude scintillations observed at a low latitude station. Data from the Global Navigation Satellite System (GNSS) Ionospheric Scintillation and Total Electron Content (TEC) monitor (GISTM) receiver installed at the Space Science Centre (ANGKASA), Institute of Climate Change, UniversitiKebangsaan Malaysia, UKM (2.92°N, 101.78°E) were used for this study. Of the 460 scintillation (by neglecting S4<0.15) events recorded during February 2014, 55% were weak (0.15≤S4<0.25), 32% were moderate (0.25≤S4 <0.35) and 13% were strong (S4 ≥0.35). For February 2014, the amplitude scintillations were most pronounced in the post-sunset time to pre-midnight time. Finally, these analysed data are used to study the variability of scintillation with solar activities.

Kriging‐based ionospheric TEC, ROTI and amplitude scintillation index (S4) maps for India

In this study, an attempt is made to develop regional ionospheric total electron content (TEC), rate of TEC index (ROTI) and amplitude scintillation index (S 4) maps using data from 26 dual-frequency global positioning system (GPS) receivers under GPS aided geo-stationary earth orbit augmented navigation programme over Indian region. One-minute spatial TEC maps are generated for the entire Indian region covering 65–100°E geographic longitudes, 5–40°N geographic latitudes with 2° × 2° grid separation using Kriging method. Also, the ROTI and amplitude scintillation index (S 4) maps for every 5 min are generated. The performance of the generated regional TEC maps is evaluated during a severe geomagnetic storm condition. Patterns of equatorial ionisation anomaly (EIA) TEC structures are investigated for St. Patrick's storm between the days 15 and 20 March 2015 with the generated TEC maps. The proposed TEC maps depict the northern crest of EIA features in latitudinal extent and TEC strength. The kriging method detects the suppressed and downshift of EIA features on 18 March 2015. The movement of plasma bubbles are analysed over Indian latitudes during the transition period of a geomagnetic storm on 17 March 2015.

Active (Evolving) Phase of Equatorial Plasma Bubbles Observed Over Tirunelveli

AbstractUsual post‐sunset generation of equatorial spread F (ESF) irregularities on quiet days (Q‐days) and midnight or post‐midnight generation of ESF on magnetically disturbed days (D‐days) is widely known. However, the duration of evolving or active phase of these freshly generated ESF (FESF) irregularities is not clearly understood. Here, the active phase duration refers to the time period during which the perturbation electric field associated with equatorial plasma bubbles drifting over Tirunelveli is alive. Recently, Gurram et al. (2018) quantified the active phase duration of FESF for both Q‐days and D‐days. It was the first exercise to obtain the average active phase duration of FESF from observations. In view of this, we carried out detailed analysis to examine their dependence on solar flux and geomagnetic activity using long‐term amplitude scintillation observations on 251‐MHz signal. It is found that percentage of days with longer active phase (td≥ 50 min) is higher on D‐days, and it is consistent for all levels of solar flux. Average duration of the active phase of FESF, ⟨td⟩, is 57.9 ± 52.3 min on D‐days and 33.8 ± 23.4 min on Q‐days. The active phase of FESF has tendency to sustain for longer time during low solar flux, which is attributed to presence of weaker ambient ionospheric electric field during that period. It is noted that FESF generated on days with stronger geomagnetic activity tend to have longer active phase. Also, days with FESF cause more moderate–strong scintillations as compared to days with drifted‐in ESF.

Degradation of Satellite‐Based Navigation Performance Observed From an Anomaly Crest Location in the Indian Longitude Sector

AbstractGPS amplitude and phase scintillations in terms of the index S4 and σϕ and the corresponding losses of lock in signal have been studied with consequent errors in receiver positions for the whole month of March 2014 from Calcutta situated near the northern crest of the equatorial ionization anomaly (EIA). The impact of phase and amplitude scintillations is found to be different on GPS satellites in terms of intensities and duration. There are 42 and 59 cases of loss of lock in C/NO and phase, respectively, all occurring during 13–18 UT (LT = UT + 06:00). For all the cases, duration of amplitude loss of lock is longer than that of phase loss of lock. Associated with such signal perturbations, deviations in receiver positions are found to occur having maximum values of 31.72 m for latitude and 85.2 m for longitude during 15–16 UT. Though 9.5% of the cases start when amplitude scintillation was moderate (0.4 &lt; S4 ≤ 0.6), 32.2% of the cases occurred when phase scintillation was moderate (0.2 &lt; σϕ ≤ 0.7). The percentage of occurrences of moderate amplitude scintillation is 5.07% during 19:00–20:00 UT and does not occur thereafter, whereas the percentage of occurrences of moderate phase scintillations are found to be 18% even during 21:00–22:00 UT. The percentage of occurrences of weak phase scintillations was also higher (49.25%) compared to 1.98% corresponding to amplitude scintillations even at 23:00 UT. Occurrence of phase scintillations on GPS links has not been frequently reported from this longitude sector before, mainly due to nonavailability of appropriate transmissions.

A Comparative Performance Analysis of GPS L1 C/A, L5 Acquisition and Tracking Stages Under Polar and Equatorial Scintillations

This article provides a comparative performance analysis of different acquisition and tracking methods of GPS L1 C/A and GPS L5 signals testing their robustness to the presence of scintillations in the propagation environment. This article compares the different acquisition methods in terms of probabilities of detection/false alarm, peak-to-noise floor ratios for the acquired signal and execution time, assessing the performance loss in the presence of scintillations. Moreover, robust tracking architectures that are optimized to operate in a harsh ionospheric environment have been employed. The performance of the carrier tracking methods, namely, traditional phase-locked loop (PLL) and Kalman filter based-PLL, have been compared in terms of the standard deviation of Doppler estimation, phase error, phase lock indicator (PLI), and phase jitter. The article is based on real global navigation satellite systems (GNSS) signals affected by significant phase and amplitude scintillation effects, collected at the South African Antarctic research base (SANAE IV) and Brazilian Centro de Radioastronomia e Astrofisica Mackenzie (CRAAM) monitoring stations. Performance is assessed exploiting a fully software GNSS receiver, which implements the different architectures. The comparative analysis allows to choose the best setting of the acquisition and tracking parameters, in order to allow the operation of signal acquisition and tracking at a required performance level under scintillation conditions.

Ionospheric S4 Scintillations from GNSS Radio Occultation (RO) at Slant Path

Ionospheric scintillation can significantly degrade the performance and the usability of space-based communication and navigation signals. Characterization and prediction of ionospheric scintillation can be made from the Global Navigation Satellite System (GNSS) radio occultation (RO) technique using the measurement from a deep slant path where the RO tangent height (ht) is far below the ionospheric sources. In this study, the L–band S4 from the RO measurements at ht = 30 km is used to infer the amplitude scintillation on the ground. The analysis of global RO data at ht = 30 km shows that sporadic–E (Es), equatorial plasma bubbles (EPBs), and equatorial spread–F (ESF) produce most of the significant S4 enhancements, although the polar S4 is generally weak. The enhanced S4 is a strong function of local time and magnetic dip angle. The Es–induced daytime S4 tends to have a negative correlation with the solar cycle at low latitudes but a positive correlation at high latitudes. The nighttime S4 is dominated by a strong semiannual variation at low latitudes.

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.

Solar Cycle Variations of GPS Amplitude Scintillation for the Polar Region

AbstractGlobal Positioning System (GPS) L1 amplitude data, obtained using the Canadian High Arctic Ionospheric Network (CHAIN) during the period 2008–2018, is used to study the seasonal and solar cycle dependence of high‐latitude amplitude scintillation. The occurrence of amplitude scintillation is predominantly confined to the 10–18 magnetic local time (MLT) and 72–87° Altitude‐Adjusted Corrected Geomagnetic (AACGM) sector and is a winter and equinoctial phenomenon. The occurrence of amplitude scintillation shows a clear seasonal and solar cycle dependence with a maximum value of ∼11% during the high solar activity early winter periods, and a secondary maximum in equinoctial months, and almost no occurrence during summer months. This pattern in occurrence suggests that amplitude scintillation is a phenomenon that is closely associated with the presence of patches and particle precipitation events.

Impacts of Ionospheric Irregularities on L-Band Geosynchronous Synthetic Aperture Radar

An L-band geosynchronous synthetic aperture radar (GEO SAR) system has to be confronted by an intractable issue of the decorrelations imposed by ionospheric irregularities. On the one hand, the phase and amplitude scintillations will bring about the decorrelation within the synthetic aperture and result in azimuth-imaging degradation. On the other hand, the imposed scintillation history is spatially decorrelated across the ultra-large GEO SAR scene. In this article, a signal model of the GEO SAR acquisitionis established with the two-way ionospheric transfer function (ITF) modulation to incorporate these two types of decorrelations. This model meanwhile takes the anisotropic and flowing irregularities into account. By using this model, the L-band GEO SAR azimuth-imaging is evaluated in terms of five indexes, whose performances are dependent on nine ionospheric parameters. Furthermore, the spatial correlation of the phase and intensity scintillation histories is investigated for the L-band GEO SAR scene, both in simulation and statistics. The statistical result implies a sized scene, in which the phase scintillation history tends to be consistent. Finally, the interferometric performance is investigated between the pure and contaminated GEO SAR images. The simulation result shows that the degradation of the interferometric coherence results from the in-aperture decorrelation.

Study of tropospheric scintillation effects in Ku-band frequency for satellite communication system

Scintillation is a rapid fluctuation of an electromagnetic waves in terms of phase and amplitude due to a small-scale inconsistency in the transmission path (or paths) with time. Scintillation exists continuously throughout a day whether during raining or clear sky conditions. The raw signal data need to exclude other propagations factors that include signal fluctuations to further understand the scintillation studies. This paper presents the analysis of tropospheric scintillation data from January 2016 till December 2016 at Ku-band frequency of 12.202 GHz beacon signal. The experimental data from MEASAT 3B were collected and analyzed to see the effect of tropospheric scintillation. The elevation angle of the dish antenna is 77.45o. The highlighted objectives are to analyze the scintillation data at Ku-band, and to compare and validate the results with other scintillation models. The result shows that the stipulated scintillation analysis has higher amplitude, which is 0.73 dB compared to other scintillation analysis which has lower scintillation amplitude: 0.45 dB (Karasawa), 0.42 dB (ITU-R), 0.4 dB (Nadirah &amp; Rafiqul), 0.42 dB (Van De Kamp) and 0.11 dB (Anthony &amp; Mandeep).