Scintillation Data Research Articles

Effect of seasonal variation on tropospheric scintillation at Ku-band in equatorial climate

One-minute tropospheric scintillation data recorded in Philippines over 3 years have been collected for analysis using a Superbird C Satellite (144°E) at 12.2 GHz with an antenna elevation angle of 58.8°. The results obtained from the analysis of seasonal variations and different tropospheric scintillation models proposed by various authors have been presented in this paper. Considerable differences between measured data and models have been observed at different percentages of time. The comparisons have been performed for both Northeast and Southwest monsoon seasons. Karasawa model gives the lowest root mean square error (3 %) compared to the other models.

A study on ionospheric scintillation near the EIA crest in relation to equatorial electrodynamics

AbstractEquatorial electrojet (EEJ) data, which are considered as a proxy index of equatorial electric field, are analyzed in conjunction with equatorial ionosonde, total electron content (TEC) and scintillation data near the equatorial ionization anomaly (EIA) crest for the equinoctial months of high solar activity years (2011–2012) to identify any precursor index of postsunset evolution of equatorial electron density irregularities and subsequent occurrence of scintillation near the northern EIA crest. Only geomagnetically quiet and normal electrojet days are considered. The diurnal profiles of EEJ on the scintillation days exhibit a secondary enhancement in the afternoon to presunset hours following diurnal peaks. A series of electrodynamical processes conducive for generation of irregularities emerge following secondary enhancement of EEJ. Latitudinal profile of TEC exhibits resurgence in EIA structure around the postsunset period. Diurnal TEC profile near the EIA crest resembles postsunset secondary enhancement on the days with afternoon enhancement in EEJ. Occurrence of equatorial spread F and postsunset scintillation near the EIA crest seems to follow the secondary enhancement events in EEJ. Both the magnitude and duration of enhanced EEJ are found to be important for postsunset intensification of EIA structure and subsequent occurrence of equatorial irregularities. A critical value combining the two may be considered an important precursor for postsunset occurrence of scintillation near the EIA crest. The results are validated using archived data for the years 1989–1990 and explained in terms of modulation effects of enhanced equatorial fountain.

On the second order statistics for GPS ionospheric scintillation modeling

AbstractEquatorial ionospheric scintillation is a phenomenon that occurs frequently, typically during nighttime, affecting radio signals that propagate through the ionosphere. Depending on the temporal and spatial distribution, ionospheric scintillation can represent a problem in the availability and precision for the Global Navigation Satellite System's users. This work is concerned with the statistical evaluation of the amplitude ionospheric scintillation fading events, namely, level crossing rate (LCR) and average fading duration (AFD). Using α‐μ model, the LCR and AFD are validated against experimental data obtained in São José dos Campos (23.1°S; 45.8°W; dip latitude 17.3°S), Brazil, a station located near the southern crest of the ionospheric equatorial ionization anomaly. The amplitude scintillation data were collected between December 2001 and January 2002, a period of high solar flux conditions. The obtained results with the proposed model fitted quite well with the experimental data and performed better when compared to the widely used Nakagami‐m model. Additionally, this work discusses the estimation of α and μ parameters, and the best fading coefficients found in this analysis are related to scintillation severity. Finally, for theoretical situations in which no set of experimental data are available, this work also presents parameterized equations to describe these fading statistics properly.

Low-latitude scintillation occurrences around the equatorial anomaly crest over Indonesia

Abstract. We investigated low-latitude ionospheric scintillation in Indonesia using two GPS receivers installed at Bandung (107.6° E, 6.9° S; magnetic latitude 17.5° S) and Pontianak (109.3° E, 0.02° S; magnetic latitude 8.9° S). This study aimed to characterise climatological and directional ionospheric scintillation occurrences, which are useful not only for the physics of ionospheric irregularities but also for practical use in GNSS (global navigation satellite system)-based navigation. We used the deployed instrument's amplitude scintillation (S4 index) data from 2009, 2010, and 2011; the yearly SSN (sunspot-smoothed numbers) were 3.1, 16.5, and 55.9, respectively. In summary, (1) scintillation occurrences in the post-sunset period (18:00–01:00 LT) during equinox months (plasma bubble season) at the two sites can be ascribed to the plasma bubble; (2) using directional analyses of the two sites, we found that the distribution of scintillation occurrences is generally concentrated between the two sites, indicating the average location of the EIA (equatorial ionisation anomaly) crest; (3) scintillation occurrence enhancements for the two sites in field-aligned directions are herein reported for the first time by ground-based observation in a low-latitude region; (4) distribution of scintillation occurrences at Pontianak are concentrated in the southern sky, especially in the southwest direction, which is very likely associated with the plasma bubble tilted westward with increasing latitude; and (5) scintillation occurrence in the post-midnight period in the non-plasma-bubble season is the most intriguing variable occurring between the two sites (i.e. post-midnight scintillations are observed more at Bandung than Pontianak). Most of the post-midnight scintillations observed at Bandung are concentrated in the northern sky, with low elevation angles. This might be due to the amplitude of irregularities in certain directions, which may be effectively enhanced by background density enhancement by the EIA and because satellite–receiver paths are longer in the EIA crest region and in a field-aligned direction.

Characterization of GNSS scintillations over Lagos, Nigeria during the minimum and ascending phases (2009–2011) of solar cycle 24

This study characterizes equatorial scintillations at L-band frequency over Lagos, Nigeria during the minimum and ascending phases of solar cycle 24. Three years (2009–2011) of amplitude scintillation data were used for the investigation. The data were grouped on daily, monthly, seasonal, and yearly scales at three levels of scintillation (weak (0.3⩽S4<0.4), moderate (0.4⩽S4<0.7), and intense (S4⩾0.7)). To ensure reliable statistical inferences, three data cut-off criteria were adopted. Scintillations were observed to have a daily trend of occurrence during the hours of 1900–0200LT, and higher levels of scintillations were localized within the hours of 2000–2300LT. On monthly basis, September and October recorded the highest occurrences of scintillation, while January recorded the least. Scintillations were recorded during all the months of 2011, except January. Surprisingly, pockets of scintillation events (weak levels) were also observed during the summer months (May, June, and July). Seasonally, equinoxes recorded the highest occurrences of scintillation, while June solstice recorded the least occurrences. Scintillation activity also increases with solar and geomagnetic activity. On a scintillation active day, the number of satellites available to the receiver’s view reduces as the duration of observation reduces. These results may support the development of future models that could provide real-time predictability of African equatorial scintillations, with a view to supporting the implementation of GNSS-based navigation for aviation applications in Africa.

Tropospheric scintillation prediction models for a high elevation angle based on measured data from a tropical region

The recent rapid evolution of new satellite services, including VSAT for internet access, LAN interconnection and multimedia applications, has triggered an increasing demand for bandwidth usage by satellite communications. However, these systems are susceptible to propagation effects that become significant as the frequency increases. Scintillation is the rapid signal fluctuation of the amplitude and phase of a radio wave, which is significant in tropical climates. This paper presents the analysis of the tropospheric scintillation data for satellite to Earth links at the Ku-band. Twelve months of data (January–December 2011) were collected and analyzed to evaluate the effect of tropospheric scintillation. Statistics were then further analyzed to inspect the seasonal, worst-month, diurnal and rain-induced scintillation effects. By employing the measured scintillation data, a modification of the Karasawa model for scintillation fades and enhancements is proposed based on data measured in Malaysia.

Yttrium antisite reduction and improved photodiode performance in Ce doped Y3Al5O12 by Czochralski growth in alumina rich melts

Single crystal cerium doped yttrium aluminum garnet boules were grown by the Czochralski method. Cerium concentrations were held at 1.0 at. % (with respect to yttrium in an on stoichiometric charge) but melt stoichiometry ranged from 10.0 at. % yttria rich to 10.0 at. % alumina rich in 5.0% increments. Photo-luminescence, lifetime, and scintillation data demonstrate a measureable decrease in UV defect emission as the melt becomes alumina rich. This is strongly consistent with a suppression of equilibrium YAl3+ antisite defect concentrations in the boule as melt stoichiometry shifts towards alumina rich. This decrease does not alter thermoluminescence behavior, making the case that carrier traps and YAl3+ antisites are independent defects. Additionally, an aluminum in-diffusion post growth treatment indicates the observed change is from reduction of YAl3+ antisite defect concentrations alone, as opposed to alteration of antisite-vacancy complexes. The results culminate in a large increase in visible emission and produce an excellent resolution of 5.04 ± 0.07% (662 keV; 10 mm thick) with electronic noise subtraction on a photodiode.

GNSS station characterisation for ionospheric scintillation applications

Ionospheric scintillations are fluctuations in the phase and amplitude of the signals from GNSS (Global Navigation Satellite Systems) occurring when they cross regions of electron density irregularities in the ionosphere. Such disturbances can cause serious degradation of several aspects of GNSS system performance, including integrity, accuracy and availability. The two indices adopted worldwide to characterise ionospheric scintillations are: the amplitude scintillation index, S4, which is the standard deviation of the received power normalised by its mean value, and the phase scintillation index, σΦ, which is the standard deviation of the de-trended carrier phase. Collaborative work between NGI and INGV supports a permanent network of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers that covers a wide range of latitudes in the northern European sector. Data from this network has contributed significantly to several papers during the past few years (see e.g. De Franceschi et al., 2008; Aquino et al., 2009; Spogli et al., 2009, 2010; Alfonsi et al., 2011). In these investigations multipath effects and noise that contaminate the scintillation measurements are largely filtered by applying an elevation angle threshold. A deeper analysis of the data quality and the development of a more complex filtering technique can improve the results obtained so far. The structures in the environment of each receiver in the network which contaminate scintillation measurements should be identified in order to improve the quality of the scintillation and TEC data by removing error sources due to the local environment. The analysis in this paper considers a data set characterised by quiet ionospheric conditions of the mid-latitude station located in Nottingham (UK), followed by a case study of the severe geomagnetic storm, which occurred in late 2003, known generally as the “Halloween Storm”.

ESWua: a tool to manage and access GNSS ionospheric data from mid-to-high latitudes

The electronic space weather upper atmosphere (eSWua) is a hardware–software system that is based on measurements collected by instruments installed by the Upper Atmosphere Physics Group of the Istituto Nazionale di Geofisica e Vulcanologia (INGV, Italy). More recently, it has also included the Global Navigation Satellite System (GNSS) ionospheric scintillation and total electron content (TEC) monitor (GISTM) stations that are managed and operated by the University of Nottingham (UK). By visiting the eSWua website, it is possible to access the database that has been implemented to organize and manage the large amount of information acquired. The section of the database designed for the TEC and scintillation data has been designed to address the needs of the space weather community as well as of scientific users. Through the web tools, it is possible to visualize, plot, extract and download the data from each station. This interactive website is supported by a structured database, and it provides a powerful tool for the scientific and technological community in the field of telecommunications and space weather. At present, the data transmission procedure, the database population algorithm, the linear plot and polar plot visualization tools, the statistics page, and the user management system are fully operational. Web access to the data and tools has been realized to handle the data from the sites at low, mid and high latitudes. In this report, we present the results of the system for the GNSS data in the Arctic, the Antarctica, and the three GISTM stations operated by the University of Nottingham: Nottingham, Trondheim and Dourbes. Case studies of the efficacy of this system for scientific and application purposes are also presented and discussed.

Modification of Karasawa tropospheric scintillation model for Malaysia climate

Tropospheric scintillation is the rapid fluctuation and degradation of satellite signals due to changes in refractive index of atmosphere. This phenomenon tends to affect signals more strongly at frequencies above 10 GHz. This paper introduces a new scintillation prediction model created by modifying the existing Karasawa model. The proposed model is compared with currently existing model using scintillation data collected in Parit Buntar, Malaysia. The proposed model can simultaneously predict scintillation intensity of both fade and enhancement scintillation with an error rate below 5 %.

Enantioselective Demethylation of Nicotine as a Mechanism for Variable Nornicotine Composition in Tobacco Leaf

Nicotine and its N-demethylation product nornicotine are two important alkaloids in Nicotiana tabacum L. (tobacco). Both nicotine and nornicotine have two stereoisomers that differ from each other at 2'-C position on the pyrrolidine ring. (S)-Nicotine is the predominant form in the tobacco leaf, whereas the (R)-enantiomer only accounts for ∼0.2% of the total nicotine pool. Despite considerable past efforts, a comprehensive understanding of the factors responsible for generating an elevated and variable enantiomer fraction of nornicotine (EF(nnic) of 0.04 to 0.75) from the consistently low EF observed for nicotine has been lacking. The objective of this study was to determine potential roles of enantioselective demethylation in the formation of the nornicotine EF. Recombinant CYP82E4, CYP82E5v2, and CYP82E10, three known tobacco nicotine demethylases, were expressed in yeast and assayed for their enantioselectivities in vitro. Recombinant CYP82E4, CYP82E5v2, and CYP82E10 demethylated (R)-nicotine 3-, 10-, and 10-fold faster than (S)-nicotine, respectively. The combined enantioselective properties of the three nicotine demethylases can reasonably account for the nornicotine composition observed in tobacco leaves, which was confirmed in planta. Collectively, our studies suggest that an enantioselective mechanism facilitates the maintenance of a reduced (R)-nicotine pool and, depending on the relative abundances of the three nicotine demethylase enzymes, can confer a high (R)-enantiomer percentage within the nornicotine fraction of the leaf.

Comparison of probability density functions for analyzing irradiance statistics due to atmospheric turbulence

A large number of model probability density functions (PDFs) are used to analyze atmospheric scintillation statistics. We have analyzed scintillation data from two different experimental setups covering a range of scintillation strengths to determine which candidate model PDFs best describe the experimental data. The PDFs were fitted to the experimental data using the method of least squares. The root-mean-squared fitting error was used to monitor the goodness of fit. The results of the fitting were found to depend strongly on the scintillation strength. We find that the log normally modulated Rician and the log normal PDFs are the best fit to the experimental data over the range of scintillation strengths encountered.

Evolution of equatorial irregularities under varying electrodynamical conditions: A multitechnique case study from Indian longitude zone

A comprehensive multitechnique study on the postsunset evolutions of equatorial ionization anomaly (EIA) and equatorial plasma density irregularities in the context of the varying electrodynamical conditions under normal equatorial electrojet (EEJ), complete and partial counter electrojet (CEJ) events is presented from the Indian longitude zone. The study involves analysis of scintillation data at VHF (250 MHz) and GPS L1 (1575.42 MHz) frequency, ionosonde data, magnetometer data along with global ionospheric maps (GIMs) of total electron content (TEC) for the vernal equinoctial months (March–April) of 2011. The investigation reveals inefficiency of the noontime peak EEJ to dictate the day‐to‐day variability of postsunset irregularity phenomena. Intensification of EEJ after ∼1530 IST (Indian standard time) on normal EEJ days and significantly enhanced residual fields presumably due to CEJ event after ∼1700 IST on complete and partial CEJ days are found to be associated with the resurgence of EIA and evolution of postsunset irregularities. The results are discussed in terms of superposition effects of electric fields arising from E‐ and F‐ region dynamos.

Neutrinoless Double Beta Decay with SNO+

SNO+ will search for neutrinoless double beta decay by loading 780 tonnes of linear alkylbenzene liquid scintillator with O(tonne) of neodymium. Using natural Nd at 0.1% loading will provide 43.7 kg of 150Nd given its 5.6% abundance and allow the experiment to reach a sensitivity to the effective neutrino mass of 100-200 meV at 90% C.L in a 3 year run. The SNO+ detector has ultra low backgrounds with 7000 tonnes of water shielding and self-shielding of the scintillator. Distillation and several other purification techniques will be used with the aim of achieving Borexino levels of backgrounds. The experiment is fully funded and data taking with light-water will commence in 2012 with scintillator data following in 2013.

An Analysis of Low-Latitude Ionospheric Scintillation and Its Effects on Precise Point Positioning

Global Positioning System (GPS) receivers at low latitudes have a high probability of experiencing severe ionospheric scintillations. This paper presents the results of scintillation characteristics and scintillation effect on GPS precise point positioning (PPP), using the data observed by the first ever GNSS scintillation monitoring receiver in Hong Kong. Ionospheric scintillation data were collected in July and August 2012 using a Septentrio PolaRxS Pro receiver located at a station (22°12′N, 114°15′E) in the south of Hong Kong. It was observed that August had much more and stronger scintillations than July in Hong Kong. Amplitude scintillation events ( 4 S ≥0.4) were frequently observed during 21:00-3:00 LT (UT+8 hour) in July and 20:004:00 LT in August. Strong scintillations ( 4 S ≥0.8 or rad 8 . 0    ) were mostly observed during 0:00-1:00 LT in July and 20:00-23:00 LT in August. The effect of scintillations on GPS positioning was evaluated using a dual-frequency PPP method. It revealed that under the impact of severe ionospheric scintillations ( 4 S ≥1.0 and   ≥1.0 rad), the largest PPP error can increase to more than 34 cm in the vertical and more than 20 cm in the horizontal components.

Ionospheric scintillation near the anomaly crest in relation to the variability of ambient ionization

Ionospheric scintillation near the anomaly crest is a matter of great concern for the design of transionospheric communication and navigation links and forecasting of the same is an important aspect of ensuing space weather scenario. Under present investigation, amplitude scintillation data at VHF/UHF, total electron content (TEC) data from Calcutta (geographic: longitude 88.38°E, latitude 22.58°N, dip: 32°N), situated virtually below the northern crest of equatorial ionization anomaly, are analyzed to study any correspondence between occurrences of postsunset equatorial scintillations and daytime ambient ionization characteristics. The study reveals distinctive features of diurnal TEC profiles on scintillation and non‐scintillation days. The differences are reflected in daytime TEC parameters like diurnal peak values of TEC, its occurrence time, 3‐dB width of diurnal TEC profile, daytime integrated TEC and average TEC level around the local sunset. The analysis reveals that local time of diurnal TEC maximum in conjunction with daytime integrated TEC values may potentially be selected to develop forecasting capability of postsunset scintillation for the equinoctial months of high solar activity years under quiet geomagnetic condition. The results are discussed in terms of sustenance probability of high ambient ionization in the postsunset period.

Interhemispheric comparison of GPS phase scintillation at high latitudes during the magnetic-cloud-induced geomagnetic storm of 5–7 April 2010

Abstract. Arrays of GPS Ionospheric Scintillation and TEC Monitors (GISTMs) are used in a comparative scintillation study focusing on quasi-conjugate pairs of GPS receivers in the Arctic and Antarctic. Intense GPS phase scintillation and rapid variations in ionospheric total electron content (TEC) that can result in cycle slips were observed at high latitudes with dual-frequency GPS receivers during the first significant geomagnetic storm of solar cycle 24 on 5–7 April 2010. The impact of a bipolar magnetic cloud of north-south (NS) type embedded in high speed solar wind from a coronal hole caused a geomagnetic storm with maximum 3-hourly Kp = 8- and hourly ring current Dst = −73 nT. The interhemispheric comparison of phase scintillation reveals similarities but also asymmetries of the ionospheric response in the northern and southern auroral zones, cusps and polar caps. In the nightside auroral oval and in the cusp/cleft sectors the phase scintillation was observed in both hemispheres at about the same times and was correlated with geomagnetic activity. The scintillation level was very similar in approximately conjugate locations in Qiqiktarjuaq (75.4° N; 23.4° E CGM lat. and lon.) and South Pole (74.1° S; 18.9° E), in Longyearbyen (75.3° N; 111.2° E) and Zhongshan (74.7° S; 96.7° E), while it was significantly higher in Cambridge Bay (77.0° N; 310.1° E) than at Mario Zucchelli (80.0° S; 307.7° E). In the polar cap, when the interplanetary magnetic field (IMF) was strongly northward, the ionization due to energetic particle precipitation was a likely cause of scintillation that was stronger at Concordia (88.8° S; 54.4° E) in the dark ionosphere than in the sunlit ionosphere over Eureka (88.1° N; 333.4° E), due to a difference in ionospheric conductivity. When the IMF tilted southward, weak or no significant scintillation was detected in the northern polar cap, while in the southern polar cap rapidly varying TEC and strong phase scintillation persisted for many hours. This interhemispheric asymmetry is explained by the difference in the location of solar terminator relative to the cusps in the Northern and Southern Hemisphere. Solar terminator was in the immediate proximity of the cusp in the Southern Hemisphere where sunlit ionospheric plasma was readily convected into the central polar cap and a long series of patches was observed. In contrast, solar terminator was far poleward of the northern cusp thus reducing the entry of sunlit plasma and formation of dense patches. This is consistent with the observed and modeled seasonal variation in occurrence of polar cap patches. The GPS scintillation and TEC data analysis is supported by data from ground-based networks of magnetometers, riometers, ionosondes, HF radars and all-sky imagers, as well as particle flux measurements by DMSP satellites.

Using TEC and radio scintillation data from the CITRIS radio beacon receiver to study low and midlatitude ionospheric irregularities

[1] Unique data on ionospheric plasma irregularities from the Naval Research Laboratory Scintillation and TEC Receiver in Space (CITRIS) instrument is presented. CITRIS is a multiband receiver that recorded Total Electron Content (TEC) and radio scintillations from Low-Earth Orbit (LEO) on STPSat1. The 555 ± 5 km altitude 35° inclination orbit covers low and midlatitudes. The measurements require propagation from a transmitter to a receiver through the F region plasma. CITRIS used both 1) satellite beacons in LEO and 2) the French sponsored global network of ground-based Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) beacons. This paper is both a brief review of the CITRIS experiment and the first combined TEC and scintillation study of ionospheric irregularities using a satellite-borne beacon receiver. It primarily focuses on CITRIS/DORIS observations and is a case study of the ionospheric irregularities and associated scintillation characteristics at 401.25 MHz during the 2008 equinox solar minimum. In addition, CITRIS was operated in a complementary fashion with the Communication/Navigations Outages Forecasting System (C/NOFS) satellite during C/NOFS' first year of operations and comparison with measured C/NOFS irregularity characteristics are made. Several types of irregularities have been studied including Spread–F and the newly discovered dawn-side depletions.

Statistics of GPS scintillations over South America at three levels of solar activity

This study characterizes low‐latitude scintillations at L‐band frequency in South America on daily, monthly, and seasonal time scales at three levels of solar activity: high, moderate and low levels. Three years (November 2001–October 2002, 2004 and 2008) of amplitude scintillation data from GPS receivers at three locations: Cuzco (14.0°S, 73.0°W, dip 1.0°S), Iquitos (3.8°S, 73.2°W, dip 7.0°N), and Bogota (4.4°N, 74.1°W, dip 16.0°N) were used for the investigation. These data were grouped into daily, monthly, and seasonal sets. We introduced tests on the data to reject signal fluctuations from non‐ionospheric sources, such as multipath from terrestrial objects. The scintillation events from the data were further classified into three levels: weak (0.3 ≤ S4 &lt; 0.4), moderate (0.4 ≤ S4 &lt; 0.7), and intense (S4 ≥ 0.7) scintillations and their monthly percentage of occurrences and durations were determined. We also used the seasonal averages of daily (1900 LT–2000 LT) TEC values to observe the variability of the equatorial anomaly using a chain of ten GPS receivers that are located at a latitudinal span of 10°N–40°S along the west coast of South America. This study concludes that GPS scintillations in this longitude sector are post‐sunset events and decay before or around local midnight, with intense activity and longer durations in the months of March and January. On seasonal time scales, the highest frequencies and longest durations of events were recorded during March Equinox and December Solstice. The months of May–July (June Solstice) had the least frequencies of occurrence and durations of events. Scintillation activity also increases with solar activity. Finally, scintillations increase in frequencies of occurrence and durations from Cuzco (near the magnetic equator) toward Bogota (near the crest of the equatorial anomaly) during solar maximum. However, a gradual collapse of the anomaly crest, away from Bogota toward Iquitos was observed as solar activity decreases, and as a result, the occurrence frequencies of scintillations at Iquitos increase relative to those at Bogota.

Development of a Real-Time Ion Spectrometer with a Scintillator for Laser-Driven Ion Acceleration Experiments

A real-time ion spectrometer mainly based on a high-resolution Thomson parabola and a plastic scintillator is designed and developed. The spectrometer is calibrated by protons from an electrostatic accelerator. The feasibility and reliability of the diagnostics are demonstrated in laser-driven ion acceleration experiments performed on the XL-II laser facility. The proton spectrum extrapolated from the scintillator data is in excellent agreement with the CR39 spectrum in terms of beam temperature and the cutoff energy. This real-time spectrometer allows an online measurement of the ion spectra in single shot, which enables efficient and statistical studies and applications in high-repetition-rate laser acceleration experiments.