Scintillation Model Research Articles

A Review of Ionospheric Scintillation Models

This is a general review of the existing climatological models of ionospheric radio scintillation for high and equatorial latitudes. Trans-ionospheric communication of radio waves from transmitter to user is affected by the ionosphere which is highly variable and dynamic in both time and space. Scintillation is the term given to irregular amplitude and phase fluctuations of the received signals and related to the electron density irregularities in the ionosphere. Key sources of ionospheric irregularities are plasma instabilities; every irregularities model is based on the theory of radio wave propagation in random media. It is important to understand scintillation phenomena and the approach of different theories. Therefore, we have briefly discussed the theories that are used to interpret ionospheric scintillation data. The global morphology of ionospheric scintillation is also discussed briefly. The most important (in our opinion) analytical and physical models of scintillation are reviewed here.

Tracking- and Scintillation-Aware Channel Model for GEO Satellite to Land Mobile Terminals at Ku-Band

Recent advances in satellite to land mobile terminal services and technologies, which utilize high frequencies with directional antennas, have made the design of an appropriate model for land mobile satellite (LMS) channels a necessity. This paper presents LMS channel model at Ku-band with features that enhance accuracy, comprehensiveness, and reliability. The effect of satellite tracking loss at different mobile terminal speeds is considered for directional mobile antenna systems, a reliable tropospheric scintillation model for an LMS scenario at tropical and temperate regions is presented, and finally a new quality indicator module for different modulation and coding schemes is included. The proposedextended LMS channel (ELMSC)model is designed based on actual experimental measurements and can be applied to narrow- and wide-band signals at different regions and at different speeds and multichannel states. The proposed model exhibits lower root mean square error (RMSE) and significant performance observation compared with the conventional model in terms of the signal fluctuations, fade depth, signal-to-noise ratio (SNR), and quality indicators accompanied for several transmission schemes.

The tropospheric scintillation prediction of earth-to-satellite link for Bangladeshi climatic condition

The performance of earth-to-satellite link largely depends on various environmental factors like rain, fog, cloud, and atmospheric effects like ionospheric and tropospheric scintillation. In this paper, the tropospheric scintillation of Bangladesh, a subtropical country, is predicted based on measured climatic parameters, like relative humidity, temperature. In this prediction, ITU scintillation model are used. Four major cities, named Dhaka, Chittagong, Rajshahi and Sylhet, of Bangladesh are selected for prediction of scintillation. From the simulation result, Rajshahi is found to be the most badly affected region by the scintillation fade depth (SFD), which is followed by Chittagong and the SFD is minimum in Dhaka and Sylhet. The difference in SFDs among the considered cities does not vary heavily. It is also found that the SFD varies from 3 dB to 13 dB depending on the frequency in used. Moreover, higher scintillation is found in rainy season of Bangladesh. During this period, the scintillation becomes double of the average figure.

Using solar wind data to predict daily GPS scintillation occurrence in the African and Asian low‐latitude regions

AbstractThe feasibility of predicting the daily occurrence of Global Positioning System scintillation events using forecasts of common geophysical indices to drive a physics‐based model of the system is demonstrated over a 5 month period for the African and Asian longitude sectors. The output from the Wing Kp model, which uses solar wind data to predict the geomagnetic activity level up to 4 h in advance, was used to drive the National Center for Atmospheric Research thermosphere/ionosphere model, from which the strength of the Rayleigh‐Taylor instability growth rate was calculated to determine the likelihood of scintillation. It is found that the physics‐based model demonstrates superior skill to an empirical scintillation model (Wideband Model (WBMOD)) in forecasting scintillation suppression events during seasons when scintillation is common. However, neither of the models driven in this way possess the ability to forecast isolated scintillation events during transitional and off‐peak seasons.

An Extended Tropospheric Scintillation Model for Free Space Optical Communication Systems

Fluctuations caused mostly by tropospheric scintillation at the free space optical receiver end have been a major problem in the rapid development of telecommunication and the increasing demands for larger bandwidth is forcing the use of free space optical (FSO) technology. This paper examined existing tropospheric scintillation models of Karasawa, Van de Kamp model, Otung, Ortgies and ITU-R, and discovered that all of them operate at the microwave range, which limits their application in FSO laser beam technology that operates in PHz frequency-range. ITU-R model was later selected owing to its global application and modified for use in FSO communication system. The new model can serve as basis for communication engineers to use as platform in the link budgetary for planning and design of low margin systems of free space optical communication link.

Global Positioning System (GPS) Positioning Errors During Ionospheric Scintillation Event

As technology advancement progresses throughout the years in this modern age, every technology has its part to play in that the world is moving towards a brighter future. GPS (Global Positioning System) has diverse application in current globalized world, its application has pervasive benefits not only to navigation and positioning, it is pivotal in industries like logistics, shipping, financial services and agriculture. Since the decision to shut down the Selectivity Availability (SA) by former U.S. President, Bill Clinton, ionospheric effect is now the primary concern of error contributing factors in GPS. Ionospheric scintillation induces rapid fluctuations in the phase and the amplitude of received Global Navigation Satellite System (GNSS) signals. These rapid fluctuations or scintillation potentially introduce cycle slips, degrade range measurements, and if severe enough lead to loss of lock in phase and code. Global Ionospheric Scintillation Model (GISM) was used to compute amplitude scintillation parameter for each GPS satellite visible from Melaka, Malaysia (Latitude 20 14’ N, Longitude 1020 16’ E) as its location has strong equatorial scintillation behavior. The output data from GISM was then used to calculate the positioning error where it is depends on the Dilution of Precision (DOP) and User Equivalent Range Error (UERE). There are two schemes that were used. First, the positioning error was calculated for all the visible satellites with better DOP but worse UERE due to scintillation event. Secondly, the positioning error was calculated for those satellites that have amplitude scintillation index, S4 < 0.7 which leads to worse DOP with better UERE. Comparison of results from the both schemes was then made.

Extended ionospheric amplitude scintillation model for GPS receivers

Ionospheric scintillation is a phenomenon that occurs after sunset, especially in the low-latitude region, affecting radio signals that propagate through the ionosphere. Depending on geophysical conditions, ionospheric scintillation may cause availability and precision problems to Global Navigation Satellite System users. The present work is concerned with the development of an extended model for describing the effects of the amplitude ionospheric scintillation on GPS receivers. Using the α-μ probabilistic model, introduced by previous authors in different contexts, the variance of GPS receiver tracking loop error may be estimated more realistically. The proposed model is developed with basis on the α-μ parameters and also considering correlation between amplitude and phase scintillation. Its results are interpreted to explain how a receiver may experience different error values under the influence of ionospheric conditions leading to a fixed scintillation level S4. The model is applied to a large experimental data set obtained at São José dos Campos, Brazil, near the peak of the equatorial anomaly during high solar flux conditions, between December 2001 and January 2002. The results from the proposed model show that depending on the α-μ pair, moderate scintillation (0.5 ≤ S4 ≤ 0.7) may be an issue for the receiver performance. When S4 > 0.7, the results indicate that the effects of scintillation are serious, leading to a reduction in the receiver availability for providing positioning solutions in approximately 50% of the cases.

Quantification of the atmospheric scintillation for laser illumination in active imaging.

Most of the analytical scintillation models used by experts to simulate the illumination performances of active imaging systems are based on the use of monochromatic, punctual, and coherent sources. These analytical models seem pessimistic regarding lightpipe-based illumination techniques. Outdoor trials have been made with 1.57 μm laser illuminators with and without lightpipe to record illumination maps and associated refractive index structure parameter C(n)2 with a propagation distance of 1 km. Analysis shows a reduction of the scintillation by a factor of 2.5 comparing analytical models and laser illumination with lightpipe.

Kinetic Monte Carlo Simulations of Scintillation Processes in NaI(Tl)

Developing a comprehensive understanding of the processes that govern the scintillation behavior of inorganic scintillators provides a pathway to optimize current scintillators and allows for the science-driven search for new scintillator materials. Recent experimental data on the excitation density dependence of the light yield of inorganic scintillators presents an opportunity to incorporate parameterized interactions between excitations in scintillation models and thus enable more realistic simulations of the nonproportionality of inorganic scintillators. Therefore, a kinetic Monte Carlo (KMC) model of elementary scintillation processes in NaI(Tl) is developed in this paper to simulate the kinetics of scintillation for a range of temperatures and Tl concentrations as well as the scintillation efficiency as a function of excitation density. The ability of the KMC model to reproduce available experimental data allows for elucidating the elementary processes that give rise to the kinetics and efficiency of scintillation observed experimentally for a range of conditions.

Impacts of Ionospheric Scintillation on the BIOMASS P-Band Satellite SAR

The European Space Agency is conducting studies for a low-earth orbiting polarimetric synthetic aperture radar called BIOMASS to provide global measurements of forest biomass and tree height. Phase scintillation across the synthetic aperture caused by ionospheric irregularities can degrade the impulse response function (IRF) and cause squinting, and its temporal variation can cause decorrelation in repeat-pass interferometry. These effects are simulated for a range of conditions for the baseline BIOMASS system configuration using the Wideband model of scintillation, which predicts that for a dawn-dusk orbit, impacts of scintillation over forest regions are negligible under all conditions except at high latitudes in the North American sector under high sunspot activity. In this sector, single-look IRFs have mean integrated sidelobe ratios (ISLRs) and peak sidelobe ratios (PSLRs) better than 0 and -5 dB, respectively, at 90% confidence interval under median solar activity up to the northern tree line ( ~ 70° geomagnetic). Degradation in the mean 3-dB resolution of up to 10% is predicted, with mean absolute azimuth shifts of the IRF peak of up to 2 m, which increases to 5 m at high sunspot number. Similar values are found for the dawn and dusk sides, and seasonal variations are negligible for latitudes below the tree line. Repeat-pass interferometric image pairs maintain coherence up to 50 ° N under median sunspot conditions. Four-look processing improves the ISLR and PSLR by several decibels, but causes significant degradation of the 3-dB resolution due to incoherent averaging of images with different random azimuth shifts.

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.

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.

Performance Comparison of OFDM based FSO Communication System under Log-normal and Gamma-Gamma Distribution

Recently, researches on Orthogonal Frequency Division Multiplexing (OFDM) based Free Space Optics (FSO) communication system gain interest since it combines the advantages of both techniques by mitigating the multipath propagation effects to improve the transmission data rate. The performance of such systems depends on base band modulation used, number of subcarriers, turbulence modeling, nature of laser beam and so on. In this paper, a performance comparison is carried out considering three different levels (weak, medium and strong) of atmospheric turbulence with log-normal and Gamma- Gamma scintillation model for plane, spherical and Gaussian beams. The Gamma-Gamma distribution analysis shows that for all kinds of laser beams, Bit Error Rate (BER) is high for weak turbulence which decreases further for medium and strong. The only difference is that the BER variation for Gamma-Gamma distribution with Gaussian beam is more prominent than for plane beam. The decrease in BER is clearly observed at higher SNR value. This kind of improvement in BER is observed with log-normal PDF at low SNR with weak turbulence. Thus we can say that weak atmospheric turbulence can be modeled by log-normal PDF and medium to strong condition can be modeled by Gamma-Gamma PDF.

Study on the Adaptability of Global Ionoshperic Scintillation Model at Low Latitude in China

为检验全球电离层闪烁模型（GISM）在中国低纬地区预测的准确性，根据2011年7月至2012年6月期间中国低纬地区三个观测站记录的GPSL1频点的电离层闪烁数据，对GISM模型的预测结果进行了分析.研究表明，在太阳活动高年，该模型能够反映出中国低纬地区闪烁的主要特征.模型预测的闪烁开始时间与观测结果较为一致，而结束时间滞后观测值约1h；模型预测的低纬地区闪烁强度峰值与观测结果基本一致，而在相同累积概率条件下，模型预测的闪烁强度则高于观测值；模型显示闪烁发生概率和闪烁强度随纬度的增加而减小，这一结果与观测结果一致.

CALORIMETRY OF GRB 030329: SIMULTANEOUS MODEL FITTING TO THE BROADBAND RADIO AFTERGLOW AND THE OBSERVED IMAGE EXPANSION RATE

We perform calorimetry on the bright gamma ray burst (GRB) 030329 by fitting simultaneously the broadband radio afterglow and the observed afterglow image size to a semi-analytic magnetohydrodynamical (MHD) and afterglow emission model. Our semi-analytic method is valid in both the relativistic and non-relativistic regimes, and incorporates a model of the interstellar scintillation that substantially effects the broadband afterglow below 10 GHz. The model is fitted to archival measurements of the afterglow flux from 1 day to 8.3 years after the burst. Values for the initial burst parameters are determined and the nature of the circumburst medium is explored. Additionally, direct measurements of the lateral expansion rate of the radio afterglow image size allow us to estimate the initial Lorentz factor of the jet.

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.

Two-year monitoring of intra-day variability of quasar 1156+295 at 4.8 GHz

The quasar 1156+295 (4C +29.45) is one of the targets in the Urumqi monitoring program which aimed to search for evidence of annual modulation in the timescales of intra-day variable (IDV) sources. The IDV observations of 1156+295 were carried out nearly monthly from October 2007 to October 2009, with the Urumqi 25m radio telescope at 4.8 GHz. The source has shown prominent IDV of total flux density in most observing sessions with variability timescales of <= 1 day at 4.8 GHz. The estimated IDV timescales seem to follow an annual cycle that can be fitted with an anisotropic interstellar scintillation (ISS) model suggesting that a significant part of the flux density variations is due to ISS. The source underwent a dramatic flare in 2008. We studied the possible consequences of the flare on the IDV of 1156+295 by comparing the changes in its IDV characteristics with the evolution of the 43 GHz Very Long Baseline Array (VLBA) core size of the source. Conclusions: The quasar 1156+295 shows evidence for an annual modulation of its IDV timescales at 4.8 GHz, the ISS-induced IDV timescales and variability strength might be affected by the overall activity state of the source core. More frequent IDV and VLBI measurements are required to confirm the relation between the IDV appearance and the core-size evolution of the source.

Evaluation of the strong turbulence impact over free-space optical links

This work expands the study of the impact of the atmospheric scintillation phenomenon in a free-space optical (FSO) communication system. Its behavior is evaluated by means of the bit error rate (BER). The contribution of our work is the BER calculation of the FSO system for different system parameters through simulations of the link combined to the already established scintillation model as the gamma–gamma model. The results show how a FSO link can be impacted by any turbulence regime.

Variation of the ionospheric scintillation index with elevation angle of the transmitter

We have analyzed GPS data from 2007–2011 to determine the nature of variation of scintillation index with elevation of the direction of propagation at an observing point Warsaw, Poland, and Hornsund, Svalbard. To compare with the theory, the intensity scintillation index is simulated as a function of elevation angle, azimuth, magnetic field inclination, and shape of irregularities, using the phase screen model of scintillation as formulated by Rino (1979). Data analysis has been done for the seasonal as well as geomagnetic activity dependence of ionospheric scintillation. Scintillation index is a power-law function of the cosecant of the elevation angle. Results show that the power law strongly depends on the form of irregularities, being larger than in isotropic case for irregularities with dimension along the magnetic field direction smaller than those across the magnetic field. The present work also shows the need to use experimentally derived dependence on elevation.

New statistical model for atmospheric optical scintillation and its application

A generic statistical model, termed Malaga, or M distribution has been proposed recently for the irradiance fluctuations. Based on this model, the irradiance has been written as a product of one term that model large-scale turbulent effects by a second term that represents the statistically independent small-scale turbulent effects. The distribution of the small-scale fluctuations has been derived in terms of the confluent hypergeometric function. The large-scale fluctuations is widely accepted to be a log-normal (LN) amplitude, however, to derive a closed-form expression for the probability density function of the M distribution, it has been modelled by Gamma distribution. It is well-known that the Gamma distribution is not a good approximation for LN distribution. Hence, in this paper, the inverse Gaussian distribution is proposed, as an alternative to the LN model. It is demonstrated that this substitution gives birth to a new statistical model, termed S distribution, which can be written in a closed-form expression and makes it possible to model accurately the irradiance fluctuations. To give an application, the performance of a wireless optical heterodyne communication system is investigated over S -distributed turbulence channel and closed-form expression is derived for the average bit error rate of the system.