Bibliografie tematiche / Ionospheric radio wave propagation

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Letteratura scientifica selezionata sul tema "Ionospheric radio wave propagation"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 29 luglio 2024

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Articoli di riviste sul tema "Ionospheric radio wave propagation"

Li, Qingfeng, Zeyun Li e Hanxian Fang. "Using 3D Ray Tracing Technology to Study the Disturbance Effect of Rocket Plume on Ionosphere". Atmosphere 13, n. 7 (20 luglio 2022): 1150. http://dx.doi.org/10.3390/atmos13071150.

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In this paper, the initial neutral atmospheric parameters, background ionospheric parameters and geomagnetic field parameters of the ionosphere are obtained by NRLMSISE-00 model, IRI-2016 model and IGRF-13 model, respectively. Considering the neutral gas diffusion process, ion chemical reaction and plasma diffusion process, a three-dimensional dynamic model of chemical substances released by rocket plume disturbing the ionosphere is constructed. The influence of the disturbance on the echo path of high frequency radio waves with different incident frequencies is simulated by using three-dimensional digital ray-tracing technology. Using this model, the process of ionospheric disturbance caused by the main chemical substances H2 and H2O in the rocket plume under three different release conditions: fixed-point release at 300 km, vertical path at 250–350 km and parabolic path at 250–350 km, and the influence of the ionospheric cavity on the radio wave propagation of high frequency radio waves at different frequencies are simulated. The main purpose of the article is to focus on the effect of the cavity generated by the rocket exhaust on the propagation of radio waves. It mainly studies the perturbation effect on the ionosphere under different release conditions, considers the neutral gas diffusion process, ion chemical reaction and plasma diffusion process, and establishes the three-dimensional dynamics of the ionospheric electron density and the spatiotemporal distribution of the plume plasma learning model. Finally, the three-dimensional ray-tracing algorithm is used to simulate the propagation path of the radio wave through the disturbance area. We considered three different release conditions, including fixed-point release, vertical path and parabolic path. The ionospheric disturbances produced by these different releases are compared and analyzed, and their effects on the propagation path of radio waves are studied.

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Krasheninnikov, I. V., e V. N. Shubin. "Features of Forecasting the Operation of Ionospheric Radio Lines in Upper Rays Modes". Геомагнетизм и аэрономия 63, n. 4 (1 luglio 2023): 473–80. http://dx.doi.org/10.31857/s0016794023600096.

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The frequency dependence of transmitted information qualitative indicators is analyzed on theexample of two meridional radio links: single-hop (~2600 km) and dominant two-hop (~5100 km) for basicmodes of radio wave propagation in the ionosphere. It is shown that the presence of highly efficient receivingtransmittingantennas in a radio communication system leads to the need to take the existence of a priori energeticallyextremely weak modes into account in the problem of radio path specification statement. In thiscase, we consider those formed exclusively by the mechanism of radiation transfer along the upper-angles raytrajectories in the ionospheric propagation of radio waves. If the angles of departure and arrival for suchmodes and the directions of the main lobes of the antenna patterns at the end points of the radio path coincide,the signal-to-noise ratio for the wave field can reach the required threshold value and ensure the successfuloperation of the radio communication system. This may expand the upper frequency limit for the passageof radio waves in the transition regions of jump propagation of radio waves in the ionosphere; it shouldbe taken into account in forecasting the operation of ionospheric radio links.

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Yang, Li-Xia, Chao Liu, Qing-Liang Li e Yu-Bo Yan. "Electromagnetic wave propagation characteristics of oblique incidence nonlinear ionospheric Langmuir disturbance". Acta Physica Sinica 71, n. 6 (2022): 064101. http://dx.doi.org/10.7498/aps.71.20211204.

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Based on the generalized Zakharov model, a numerical model of electromagnetic wave propagating in the ionosphere at different angles is established by combining the finite difference time domain (FDTD) method of obliquely incident plasma with the double hydrodynamics equation and through equivalently transforming the two-dimensional Maxwell equation into one-dimensional Maxwell equation and the plasma hydrodynamics equation. In this paper. the dominant equation of Z-wave in obliquely incident nonlinear ionospheric plasma having been analyzed and deduced, the FDTD algorithm suitable for calculating the propagation characteristics of ionospheric electromagnetic wave is deduced. The simulation results prove the accuracy and effectiveness of this method for the Langmuir disturbance caused by electromagnetic wave heating the ionosphere at a small inclination angle. The results show that under small angle incidence, the high-power high-frequency electromagnetic wave excites the Langmuir wave near the O-wave reflection point in the ionospheric plasma. At the same time, the wave particle interaction causes the O-wave to convert into Z-wave and propagate into the higher region of the ionosphere. In this work, the electromagnetic wave propagation characteristics are further studied based on ionospheric plasma, which is helpful in laying the foundation of numerical algorithm for comprehensively and in depth analyzing the influence of ionospheric Langmuir disturbance on ionospheric radio wave propagation characteristics.

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LaBelle, J. "High-latitude propagation studies using a meridional chain of LF/MF/HF receivers". Annales Geophysicae 22, n. 5 (8 aprile 2004): 1705–18. http://dx.doi.org/10.5194/angeo-22-1705-2004.

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Abstract. For over a decade, Dartmouth College has operated programmable radio receivers at multiple high-latitude sites covering the frequency range 100-5000kHz with about a 1-s resolution. Besides detecting radio emissions of auroral origin, these receivers record characteristics of the ionospheric propagation of natural and man-made signals, documenting well-known effects, such as the diurnal variation in the propagation characteristics of short and long waves, and also revealing more subtle effects. For example, at auroral zone sites in equinoctial conditions, the amplitudes of distant transmissions on MF/HF frequencies are often enhanced by a few dB just before they fade away at dawn. The polarization and/or direction of the arrival of ionospherically propagating signals in the lower HF range (3-5MHz) show a consistent variation between pre-midnight, post-midnight, and pre-dawn conditions. As is well known, magnetic storms and substorms dramatically affect ionospheric propagation; data from multiple stations spanning the invariant latitude range 67-79° reveal spatial patterns of propagation characteristics associated with magnetic storms and substorms. For example, in the hours preceding many isolated substorms, favorable propagation conditions occur at progressively lower latitudes as a function of time preceding the substorm onset. For some of these effects, explanations follow readily from elementary ionospheric physics, but understanding others requires further investigation.Key words. Magnetospheric physics (annual phenomena) – Radio science (ionosphere propagation; radio-wave propagation)6

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Pavelyev, A. G., Y. A. Liou, K. Zhang, C. S. Wang, J. Wickert, T. Schmidt, V. N. Gubenko, A. A. Pavelyev e Y. Kuleshov. "Identification and localization of layers in the ionosphere using the eikonal and amplitude of radio occultation signals". Atmospheric Measurement Techniques 5, n. 1 (4 gennaio 2012): 1–16. http://dx.doi.org/10.5194/amt-5-1-2012.

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Abstract. By using the CHAllenge Minisatellite Payload (CHAMP) radio occultation (RO) data, a description of different types of the ionospheric impacts on the RO signals at the altitudes 30–90 km of the RO ray perigee is given and compared with the results of measurements obtained earlier in the satellite-to-Earth communication link at frequency 1.5415 GHz. An analytical model is introduced for describing propagation of radio waves in a stratified medium consisting of sectors with spherically symmetric refractivity distribution. This model gives analytical expressions for the phase, bending angle, and refractive attenuation of radio waves and is applied to the analysis of radio wave propagation phenomena along an extended path including the atmosphere and two parts of the ionosphere. The model explains significant amplitude and phase variations at altitudes 30–90 km of the RO ray perigee and attributes them to inclined ionospheric layers. Based on this analytical model, an innovative technique is introduced to locate layers in the atmosphere and ionosphere. A necessary and sufficient criterion is obtained for a layer to be located at the RO ray perigee. This criterion gives both qualitative and quantitative estimation of the displacement of an ionospheric and/or atmospheric layer from the RO ray perigee. This is important, in particular, for determining the location of wind shears and directions of the internal wave propagation in the lower ionosphere, and, possibly, in the atmosphere.

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Leyser, Thomas B., H. Gordon James, Björn Gustavsson e Michael T. Rietveld. "Evidence of <i>L</i>-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith". Annales Geophysicae 36, n. 1 (21 febbraio 2018): 243–51. http://dx.doi.org/10.5194/angeo-36-243-2018.

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Abstract. The response of ionospheric plasma to pumping by powerful HF (high frequency) electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association) Heating facility in magnetic zenith. The CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer) spacecraft in the topside ionosphere above the F-region density peak detected transionospheric pump radiation, although the pump frequency was below the maximum ionospheric plasma frequency. The pump wave is deduced to arrive at CASSIOPE through L-mode propagation and associated double (O to Z, Z to O) conversion in pump-induced radio windows. L-mode propagation allows the pump wave to reach higher plasma densities and higher ionospheric altitudes than O-mode propagation so that a pump wave in the L-mode can facilitate excitation of upper hybrid phenomena localized in density depletions in a larger altitude range. L-mode propagation is therefore suggested to be important in explaining the magnetic zenith effect. Keywords. Space plasma physics (active perturbation experiments)

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Danskin, D. W., A. V. Koustov, T. Ogawa, N. Nishitani, S. Nozawa, S. E. Milan, M. Lester e D. Andre. "On the factors controlling occurrence of F-region coherent echoes". Annales Geophysicae 20, n. 9 (30 settembre 2002): 1385–97. http://dx.doi.org/10.5194/angeo-20-1385-2002.

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Abstract. Several factors are known to control the HF echo occurrence rate, including electron density distribution in the ionosphere (affecting the propagation path of the radar wave), D-region radio wave absorption, and ionospheric irregularity intensity. In this study, we consider 4 days of CUTLASS Finland radar observations over an area where the EISCAT incoherent scatter radar has continuously monitored ionospheric parameters. We illustrate that for the event under consideration, the D-region absorption was not the major factor affecting the echo appearance. We show that the electron density distribution and the radar frequency selection were much more significant factors. The electron density magnitude affects the echo occurrence in two different ways. For small F-region densities, a minimum value of 1 × 1011 m-3 is required to have sufficient radio wave refraction so that the orthogonality (with the magnetic field lines) condition is met. For too large densities, radio wave strong "over-refraction" leads to the ionospheric echo disappearance. We estimate that the over-refraction is important for densities greater than 4 × 1011 m-3. We also investigated the backscatter power and the electric field magnitude relationship and found no obvious relationship contrary to the expectation that the gradient-drift plasma instability would lead to stronger irregularity intensity/echo power for larger electric fields.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; auroral ionosphere)

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Mabie, Justin, e Terence Bullett. "Multiple Cusp Signatures in Ionograms Associated with Rocket-Induced Infrasonic Waves". Atmosphere 13, n. 6 (12 giugno 2022): 958. http://dx.doi.org/10.3390/atmos13060958.

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We are interested in understanding how and when infrasonic waves propagate in the thermosphere, specifying the physical properties of those waves, and understanding how they affect radio wave propagation. We use a combination of traditional ionosonde observations and fixed frequency Doppler soundings to make high quality observations of vertically propagating infrasonic waves in the lower thermosphere/bottom side ionosphere. The presented results are the first simultaneous observations of infrasonic wave-induced deformations in ionograms and high-time-resolution observations of corresponding plasma displacements. Deformations in ionospheric echoes, which manifest as additional cusps and range variations, are shown to be caused by infrasonic wave-induced plasma displacements.

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Riabova, S. A., E. V. Olshanskaya e S. L. Shalimov. "Response of the Lower and Upper Ionosphere to Earthquakes in Turkey on February 6, 2023". Физика земли 2023, n. 6 (1 novembre 2023): 153–62. http://dx.doi.org/10.31857/s0002333723060182.

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Abstract—Ground-based magnetometers and ionospheric radio probing by means of GPS were used to analyze and interpret specific variations of the geomagnetic field and the total electron content of the ionosphere during strong catastrophic earthquakes in Turkey on February 6, 2023. It is shown that the ionospheric responses to these earthquakes recorded at distances of 1200–1600 km from the epicentre in the lower ionosphere and at distances of up to 500 km from the epicentre in the upper ionosphere can be interpreted in terms of the propagation of the Rayleigh seismic wave and atmospheric waves – shock, acoustic and internal, that is, those waves that are generated by the earthquake itself. The energy of seismic events was estimated from the ionospheric response.

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Waters, C. L., T. K. Yeoman, M. D. Sciffer, P. Ponomarenko e D. M. Wright. "Modulation of radio frequency signals by ULF waves". Annales Geophysicae 25, n. 5 (4 giugno 2007): 1113–24. http://dx.doi.org/10.5194/angeo-25-1113-2007.

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Abstract. The ionospheric plasma is continually perturbed by ultra-low frequency (ULF; 1–100 mHz) plasma waves that are incident from the magnetosphere. In this paper we present a combined experimental and modeling study of the variation in radio frequency of signals propagating in the ionosphere due to the interaction of ULF wave energy with the ionospheric plasma. Modeling the interaction shows that the magnitude of the ULF wave electric field, e, and the geomagnetic field, B0, giving an e×B0 drift, is the dominant mechanism for changing the radio frequency. We also show how data from high frequency (HF) Doppler sounders can be combined with HF radar data to provide details of the spatial structure of ULF wave energy in the ionosphere. Due to spatial averaging effects, the spatial structure of ULF waves measured in the ionosphere may be quite different to that obtained using ground based magnetometer arrays. The ULF wave spatial structure is shown to be a critical parameter that determines how ULF wave effects alter the frequency of HF signals propagating through the ionosphere.

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Più fonti

Tesi sul tema "Ionospheric radio wave propagation"

Tshisaphungo, Mpho. "Validation of high frequency propagation prediction models over Africa". Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1015239.

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The ionosphere is an important factor in high frequency (HF) radio propagation providing an opportunity to study ionospheric variability as well as the space weather conditions under which HF communication can take place. This thesis presents the validation of HF propagation conditions for the Ionospheric Communication Enhanced Profile Analysis and Circuit (ICEPAC) and Advanced Stand Alone Prediction System (ASAPS) models over Africa by comparing predictions with the measured data obtained from the International Beacon Project (IBP). Since these models were not developed using information on the African region, a more accurate HF propagation prediction tool is required. Two IBP transmitter stations are considered, Ruaraka, Kenya (1.24°S, 36.88°E) and Pretoria, South Africa (25.45°S, 28.10°E) with one beacon receiver station located in Hermanus, South Africa (34.27°S, 19.l2°E). The potential of these models in terms of HF propagation conditions is illustrated. An attempt to draw conclusions for future improvement of the models is also presented. Results show a low prediction accuracy for both ICEPAC and ASAPS models, although ICEPAC provided more accurate predictions for daily HF propagation conditions. This thesis suggests that the development of a new HF propagation prediction tool for the African region or the modification of one of the existing models to accommodate the African region, taking into account the importance of the African ionospheric region, should be considered as an option to ensure more accurate HF Propagation predictions over this region.

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Pathan, Bashir Mohammed. "Studies of low latitude ionosphere through satellite radio wave propagation". Thesis, IIG, 1994. http://localhost:8080/xmlui/handle/123456789/1566.

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Mercer, Christopher Crossley. "The search for an ionospheric model suitable for real-time applications in HF radio communications". Thesis, Rhodes University, 1994. http://hdl.handle.net/10962/d1005274.

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Statement of work: In essence the research work was to focus on the development of an ionospheric model suitable for real time HF frequency prediction and direction finding applications. The modelling of the ionosphere had to be generic in nature, sufficient to ensure that the CSIR could simultaneously secure commercial competitiveness in each of the three niche market areas aforementioned, while requiring only minimal changes to software architecture in the case of each application. A little research quickly showed that the development of an ionospheric model capable of driving a HFDFSSL system in "real time" would result in one having to make only slight re-structuring of the software to facilitate application of the same model in the areas of real time frequency prediction and spectrum management. The decision made at the outset of the project to slant the research toward the development of a model best suited for HF direction finding applications is reflected in the avenues followed during the course of the modelling process

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De, Larquier Sebastien. "The mid-latitude ionosphere under quiet geomagnetic conditions: propagation analysis of SuperDARN radar observations from large ionospheric perturbations". Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/24770.

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The Earth's ionosphere is a dynamic environment strongly coupled to the neutral atmosphere, magnetosphere and solar activity. In the context of this research, we restrict our interest to the mid-latitude (a.k.a., sub-auroral) ionosphere during quiet geomagnetic conditions. The Super Dual Auroral Radar Network (SuperDARN) is composed of more than 30 low-power High Frequency (HF, from 8-18 MHz) Doppler radars covering the sub-auroral, auroral and polar ionosphere in both hemispheres. SuperDARN radars rely on the dispersive properties of the ionosphere at HF to monitor dynamic features of the ionosphere. Though originally designed to follow auroral expansion during active periods, mid-latitude SuperDARN radars have observed ground and ionospheric scatter revealing several interesting features of the mid-latitude ionosphere during periods of moderate to low geomagnetic activity. The past 7 years' expansion of SuperDARN to mid-latitudes, combined with the recent extended solar minimum, provides large-scale continuous views of the sub-auroral ionosphere for the first time. We have leveraged these circumstances to study prominent and recurring features of the mid-latitude ionosphere under quiet geomagnetic conditions. First, we seek to establish a better model of HF propagation effects on SuperDARN observations. To do so, we developed a ray-tracing model coupled with the International Reference Ionosphere (IRI). This model is tested against another well established ray-tracing model, then optimized to be compared to SuperDARN observations (Chapter 2). The first prominent ionospheric feature studied is an anomaly in the standard ionospheric model of photo-ionization and recombination. This type of event provides an ideal candidate for testing the ray-tracing model and analyzing propagation effects in SuperDARN observations. The anomaly was first observed in ground backscatter occurring around sunset for the Blackstone, VA SuperDARN radar. We established that it is related to an unexpected enhancement in electron densities that leads to increased refraction of the HF signals. Using the ray-tracing, IRI model, and measurements from the Millstone Hill Incoherent Scatter Radar (ISR), we showed that this enhancement is part of a global phenomenon in the Northern Hemisphere, and is possibly related to the Southern Hemisphere's Weddell Sea Anomaly. We also tested a potential mechanism involving thermospheric winds and geomagnetic field configuration which showed promising results and will require further modeling to confirm (Chapter 3). The second ionospheric feature was a type of decameter-scale irregularity associated with very low drift velocities. Previous work had established that these irregularities occur throughout the year, during nighttime, and equatorward of both the auroral regions and the plasmapause boundary. An initial analysis suggested that the Temperature Gradient Instability (TGI) was responsible for the growth of such irregularities. We first used our ray-tracing model to distinguish between HF propagation effects and irregularity occurrence in SuperDARN observations. This revealed the irregularities to be widespread within the mid-latitude ionosphere and located in the bottom-side F-region (Chapter 4). A second study using measurements from the Millstone Hill ISR revealed that TGI driven growth was possible but only in the top-side F-region ionosphere. We found that initial growth may occur primarily at larger wavelengths, with subsequent cascade to decameter-scale with coupling throughout the F-region (Chapter 5). In summary, the research conducted during this PhD program has established a robust method to analyze quiet-time SuperDARN observations. It also furthered our physical understanding of some prominent features of the mid-latitude ionosphere. It leaves behind a flexible ray-tracing model, multiple online tools to browse SuperDARN data, and a thorough and growing Space Science API providing access to multiple datasets, models and visualization tools.
Ph. D.

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Löfås, Henrik. "Ionospheric modification by powerful HF-waves : Underdense F-region heating by X-Mode". Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121898.

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Observations of modifications of the electron temperature in the F-region produced by powerful high-frequency waves transmitted in X-mode are presented. The experiments were performed during quiet nighttime conditions with low ionospheric densities so no reflections occurred. Nevertheless temperature enhancements of the order of 300-400K were obtained. The modifications found can be well described by the theory of Ohmic heating by the pump wave and both temporal and spatial changes are reproduced. A brief overview of several different experimental campaigns at EISCAT facilities in the period from October 2006 to February 2008 are also given pointing out some interesting features from the different experiments. The main focus is then on the campaign during October 2006 and modifications of the electron temperature in the F-region.

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Botai, Ondego Joel. "Ionospheric total electron content variability and its influence in radio astronomy". Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1005258.

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Ionospheric phase delays of radio signals from Global Positioning System (GPS) satellites have been used to compute ionospheric Total Electron Content (TEC). An extended Chapman profle model is used to estimate the electron density profles and TEC. The Chapman profle that can be used to predict TEC over the mid-latitudes only applies during day time. To model night time TEC variability, a polynomial function is fitted to the night time peak electron density profles derived from the online International Reference Ionosphere (IRI) 2001. The observed and predicted TEC and its variability have been used to study ionospheric in°uence on Radio Astronomy in South Africa region. Di®erential phase delays of the radio signals from Radio Astronomy sources have been simulated using TEC. Using the simulated phase delays, the azimuth and declination o®sets of the radio sources have been estimated. Results indicate that, pointing errors of the order of miliarcseconds (mas) are likely if the ionospheric phase delays are not corrected for. These delays are not uniform and vary over a broad spectrum of timescales. This implies that fast frequency (referencing) switching, closure phases and fringe ¯tting schemes for ionospheric correction in astrometry are not the best option as they do not capture the real state of the ionosphere especially if the switching time is greater than the ionospheric TEC variability. However, advantage can be taken of the GPS satellite data available at intervals of a second from the GPS receiver network in South Africa to derive parameters which could be used to correct for the ionospheric delays. Furthermore GPS data can also be used to monitor the occurrence of scintillations, (which might corrupt radio signals) especially for the proposed, Square Kilometer Array (SKA) stations closer to the equatorial belt during magnetic storms and sub-storms. A 10 minute snapshot of GPS data recorded with the Hermanus [34:420 S, 19:220 E ] dual frequency receiver on 2003-04-11 did not show the occurrence of scintillations. This time scale is however too short and cannot be representative. Longer time scales; hours, days, seasons are needed to monitor the occurrence of scintillations.

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Oronsaye, Samuel Iyen Jeffrey. "Updating the ionospheric propagation factor, M(3000)F2, global model using the neural network technique and relevant geophysical input parameters". Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1001609.

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This thesis presents an update to the ionospheric propagation factor, M(3000)F2, global empirical model developed by Oyeyemi et al. (2007) (NNO). An additional aim of this research was to produce the updated model in a form that could be used within the International Reference Ionosphere (IRI) global model without adding to the complexity of the IRI. M(3000)F2 is the highest frequency at which a radio signal can be received over a distance of 3000 km after reflection in the ionosphere. The study employed the artificial neural network (ANN) technique using relevant geophysical input parameters which are known to influence the M(3000)F2 parameter. Ionosonde data from 135 ionospheric stations globally, including a number of equatorial stations, were available for this work. M(3000)F2 hourly values from 1976 to 2008, spanning all periods of low and high solar activity were used for model development and verification. A preliminary investigation was first carried out using a relatively small dataset to determine the appropriate input parameters for global M(3000)F2 parameter modelling. Inputs representing diurnal variation, seasonal variation, solar variation, modified dip latitude, longitude and latitude were found to be the optimum parameters for modelling the diurnal and seasonal variations of the M(3000)F2 parameter both on a temporal and spatial basis. The outcome of the preliminary study was applied to the overall dataset to develop a comprehensive ANN M(3000)F2 model which displays a remarkable improvement over the NNO model as well as the IRI version. The model shows 7.11% and 3.85% improvement over the NNO model as well as 13.04% and 10.05% over the IRI M(3000)F2 model, around high and low solar activity periods respectively. A comparison of the diurnal structure of the ANN and the IRI predicted values reveal that the ANN model is more effective in representing the diurnal structure of the M(3000)F2 values than the IRI M(3000)F2 model. The capability of the ANN model in reproducing the seasonal variation pattern of the M(3000)F2 values at 00h00UT, 06h00UT, 12h00UT, and l8h00UT more appropriately than the IRI version is illustrated in this work. A significant result obtained in this study is the ability of the ANN model in improving the post-sunset predicted values of the M(3000)F2 parameter which is known to be problematic to the IRI M(3000)F2 model in the low-latitude and the equatorial regions. The final M(3000)F2 model provides for an improved equatorial prediction and a simplified input space that allows for easy incorporation into the IRI model.

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Habarulema, John Bosco. "A contribution to TEC modelling over Southern Africa using GPS data". Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005241.

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Modelling ionospheric total electron content (TEC) is an important area of interest for radio wave propagation, geodesy, surveying, the understanding of space weather dynamics and error correction in relation to Global Navigation Satellite Systems (GNNS) applications. With the utilisation of improved ionosonde technology coupled with the use of GNSS, the response of technological systems due to changes in the ionosphere during both quiet and disturbed conditions can be historically inferred. TEC values are usually derived from GNSS measurements using mathematically intensive algorithms. However, the techniques used to estimate these TEC values depend heavily on the availability of near-real time GNSS data, and therefore, are sometimes unable to generate complete datasets. This thesis investigated possibilities for the modelling of TEC values derived from the South African Global Positioning System (GPS)receiver network using linear regression methods and artificial neural networks (NNs). GPS TEC values were derived using the Adjusted Spherical Harmonic Analysis (ASHA) algorithm. Considering TEC and the factors that influence its variability as “dependent and independent variables” respectively, the capabilities of linear regression methods and NNs for TEC modelling were first investigated using a small dataset from two GPS receiver stations. NN and regression models were separately developed and used to reproduce TEC fluctuations at different stations not included in the models’ development. For this purpose, TEC was modelled as a function of diurnal variation, seasonal variation, solar and magnetic activities. Comparative analysis showed that NN models provide predictions of GPS TEC that were an improvement on those predicted by the regression models developed. A separate study to empirically investigate the effects of solar wind on GPS TEC was carried out. Quantitative results indicated that solar wind does not have a significant influence on TEC variability. The final TEC simulation model developed makes use of the NN technique to find the relationship between historical TEC data variations and factors that are known to influence TEC variability (such as solar and magnetic activities, diurnal and seasonal variations and the geographical locations of the respective GPS stations) for the purposes of regional TEC modelling and mapping. The NN technique in conjunction with interpolation and extrapolation methods makes it possible to construct ionospheric TEC maps and to analyse the spatial and temporal TEC behaviour over Southern Africa. For independent validation, modelled TEC values were compared to ionosonde TEC and the International Reference Ionosphere (IRI) generated TEC values during both quiet and disturbed conditions. This thesis provides a comprehensive guide on the development of TEC models for predicting ionospheric variability over the South African region, and forms a significant contribution to ionospheric modelling efforts in Africa.

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Nordblad, Erik. "Opening New Radio Windows and Bending Twisted Beams". Doctoral thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-158797.

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In ground based high frequency (HF) radio pumping experiments, absorption of ordinary (O) mode pump waves energises the ionospheric plasma, producing optical emissions and other effects. Pump-induced or natural kilometre-scale field-aligned density depletions are believed to play a role in self-focussing phenomena such as the magnetic zenith (MZ) effect, i.e., the increased plasma response observed in the direction of Earth's magnetic field. Using ray tracing, we study the propagation of ordinary (O) mode HF radio waves in an ionosphere modified by density depletions, with special attention to transmission through the radio window (RW), where O mode waves convert into the extraordinary (X, or Z) mode. The depletions are shown to shift the position of the RW, or to introduce RWs at new locations. In a simplified model neglecting absorption, we estimate the wave electric field strength perpendicular to the magnetic field at altitudes normally inaccessible. This field could excite upper hybrid waves on small scale density perturbations. We also show how transmission and focussing combine to give stronger fields in some directions, notably at angles close to the MZ, with possible implications for the MZ effect. In a separate study, we consider electromagnetic (e-m) beams with helical wavefronts (i.e., twisted beams), which are associated with orbital angular momentum (OAM). By applying geometrical optics to each plane wave component of a twisted nonparaxial e-m Bessel beam, we calculate analytically the shift of the beam's centre of gravity during propagation perpendicularly and obliquely to a weak refractive index gradient in an isotropic medium. In addition to the so-called Hall shifts expected from paraxial theory, the nonparaxial treatment reveals new shifts in both the transverse and lateral directions. In some situations, the new shifts should be significant also for nearly paraxial beams.

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Opperman, B. D. L. "Reconstructing ionospheric TEC over South Africa using signals from a regional GPS network". Thesis, Rhodes University, 2008. http://hdl.handle.net/10962/d1005273.

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Radio signals transmitted by GPS satellites orbiting the Earth are modulated as they propagate through the electrically charged plasmasphere and ionosphere in the near-Earth space environment. Through a linear combination of GPS range and phase measurements observed on two carrier frequencies by terrestrial-based GPS receivers, the ionospheric total electron content (TEC) along oblique GPS signal paths may be quantified. Simultaneous observations of signals transmitted by multiple GPS satellites and observed from a network of South African dual frequency GPS receivers, constitute a spatially dense ionospheric measurement source over the region. A new methodology, based on an adjusted spherical harmonic (ASHA) expansion, was developed to estimate diurnal vertical TEC over the region using GPS observations over the region. The performance of the ASHA methodology to estimate diurnal TEC and satellite and receiver differential clock biases (DCBs) for a single GPS receiver was first tested with simulation data and subsequently applied to observed GPS data. The resulting diurnal TEC profiles estimated from GPS observations compared favourably to measurements from three South African ionosondes and two other GPS-based methodologies for 2006 solstice and equinox dates. The ASHA methodology was applied to calculating diurnal two-dimensional TEC maps from multiple receivers in the South African GPS network. The space physics application of the newly developed methodology was demonstrated by investigating the ionosphere’s behaviour during a severe geomagnetic storm and investigating the long-term ionospheric stability in support of the proposed Square Kilometre Array (SKA) radio astronomy project. The feasibility of employing the newly developed technique in an operational near real-time system for estimating and dissimenating TEC values over Southern Africa using observations from a regional GPS receiver network, was investigated.

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Libri sul tema "Ionospheric radio wave propagation"

Davies, Kenneth. Ionospheric radio. London, U.K: P. Peregrinus on behalf of the Institution of Electrical Engineers, 1989.

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A, Zherebt͡s︡ov G., e Sibirskiĭ institut zemnogo magnetizma, ionosfery i rasprostranenii͡a︡ radiovoln., a cura di. Fizika ionosfery i rasprostranenii͡a︡ radiovoln: Sbornik nauchnykh trudov. Moskva: "Nauka", 1988.

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A, Zherebt͡s︡ov G., Tashchilin A. V e Sibirskiĭ institut zemnogo magnetizma ionosfery i rasprostranenii͡a︡ radiovoln., a cura di. Fizika ionosfery i rasprostranenii͡a︡ radiovoln: Sbornik nauchnykh trudov. Moskva: Nauka, 1989.

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McNamara, L. F. The ionosphere: Communications, surveillance, and direction finding. Malabar, Fla: Krieger Pub. Co., 1991.

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Laboratory), Ionospheric Effects Symposium (6th 1990 Naval Research. The effect of the ionosphere on radiowave signals and system performance: Based on Ionospheric Effects Symposium, 1-3 May 1990. [Washington, DC: U.S. G.P.O., 1990.

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Gurevich, Aleksandr Viktorovich. Long distance propagation of HF radio waves. Berlin: Springer-Verlag, 1985.

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McNamara, L. F. Radio amateurs guide to the ionosphere. Malabar, Fla: Krieger Pub., 1994.

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Rawer, K. Wave propagation in the ionosphere. Dordrecht: Kluwer Academic, 1993.

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S, I͡A︡mpolʹskiĭ V., e Omskiĭ gosudarstvennyĭ pedagogicheskiĭ institut imeni A.M. Gorʹkogo., a cura di. Radiofizika i issledovanie svoĭstv veshchestva. Omsk: Omskiĭ gos. pedagog. in-t im. A.M. Gorʹkogo, 1990.

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Rawer, Karl. Wave Propagation in the Ionosphere. Dordrecht: Springer Netherlands, 1993.

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Capitoli di libri sul tema "Ionospheric radio wave propagation"

Rawer, Karl. "Propagation of radio waves in a cold magnetoplasma". In Wave Propagation in the Ionosphere, 53–66. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-017-3665-7_7.

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Larsen, Trygve R. "Irregular Variations in the High Latitude Ionosphere and their Effects on Propagation". In ELF-VLF Radio Wave Propagation, 171–85. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-010-2265-1_14.

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Rawer, Karl. "Refraction of radio waves in a plasma. Simplest case". In Wave Propagation in the Ionosphere, 7–18. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-017-3665-7_2.

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Gurevich, Alexsandr V., e Elena E. Tsedilina. "Regularities of Very Long-Distance Radio Wave Propagation in the Ionosphere". In Physics and Chemistry in Space, 71–119. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/978-3-642-70249-5_4.

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Dorman, Lev I. "Air Ionization by CR, Influence on the Ionosphere and Radio Wave Propagation". In Astrophysics and Space Science Library, 541–72. Dordrecht: Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-1-4020-2113-8_12.

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Pal, Sujay. "Remote Sensing of the Ignorosphere: Need for a Complete Earth-Ionosphere Radio Wave Propagation Model". In Astrophysics and Space Science Proceedings, 527–43. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-94607-8_41.

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Basak, Tamal. "Quantitative Modeling of Lower Ionospheric Response Due to Solar X-ray Flare: A Propagating Radio Wave Simulation Approach". In Astrophysics and Space Science Proceedings, 561–70. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-94607-8_43.

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Akinian, S. T., E. I. Mogilevskii e V. V. Fomichev. "Radio Astronomy Studies of the Sun at the Institute of Terrestrial Magnetism, the Ionosphere and Radio-Wave Propagation of the USSR Academy of Sciences". In A Brief History of Radio Astronomy in the USSR, 225–29. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-94-007-2834-9_10.

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Smol’kov, G. Y. "The Birth and Development of Radio Astronomy Studies of the Sun at the Siberian Institute of Terrestrial Magnetism, the Ionosphere and Radio-Wave Propagation". In A Brief History of Radio Astronomy in the USSR, 231–36. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-94-007-2834-9_11.

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Cander, Ljiljana R. "Ionosphere Space Weather and Radio Propagation". In Ionospheric Space Weather, 197–243. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-99331-7_8.

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Atti di convegni sul tema "Ionospheric radio wave propagation"

Bakhmet'eva, Natalia, Valery Vyakhirev, Elena Kalinina, Ilya Zhemyakov e Grigory Vinogradov. "Vertical Motions in the Lower Ionosphere and Dynamics of the Ionospheric Plasma". In 2019 Russian Open Conference on Radio Wave Propagation (RWP). IEEE, 2019. http://dx.doi.org/10.1109/rwp.2019.8810386.

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Deminov, Marat G., e Rafael G. Deminov. "Geomagnetic Index for Intense Ionospheric Storm". In 2019 Russian Open Conference on Radio Wave Propagation (RWP). IEEE, 2019. http://dx.doi.org/10.1109/rwp.2019.8810384.

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Guo, Qiang, Leonid F. Chernogor, Konstantin P. Garmash, Yiyang Luo, Victor T. Rozumenko e Yu Zheng. "Ionospheric Disturbances and Their Impacts on HF Radio Wave Propagation". In 2021 XXXIVth General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS). IEEE, 2021. http://dx.doi.org/10.23919/ursigass51995.2021.9560548.

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Ma Bao-Ke e Guo Li-Xin. "Study on scintillation of radio wave propagation through the ionospheric irregularities". In 2008 8th International Symposium on Antennas, Propagation & EM Theory (ISAPE - 2008). IEEE, 2008. http://dx.doi.org/10.1109/isape.2008.4735230.

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Maltseva, O. A., N. S. Mozhaeva, T. V. Nikitenko e T. T. Quang. "HF radio wave propagation in conditions of prolonged low solar activity". In 12th IET International Conference on Ionospheric Radio Systems and Techniques (IRST 2012). IET, 2012. http://dx.doi.org/10.1049/cp.2012.0402.

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Repin, Andrey, Mikhail Anishin, Boris Barabashov, Dmitry Demin, Valentina Denisova, Sergey Zhuravlev, Nadezhda Kotonayeva e Konstantin Tsybulya. "The Long- and Short-Term Ionospheric Forecast Service for the Shortwave Propagation". In 2019 Russian Open Conference on Radio Wave Propagation (RWP). IEEE, 2019. http://dx.doi.org/10.1109/rwp.2019.8810196.

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Ratovsky, Konstantin G., Maxim V. Klimenko, Yury V. Yasyukevich e Vladimir V. Klimenko. "Statistical Analysis of Ionospheric Global Electron Content Response to Geomagnetic Storms". In 2019 Russian Open Conference on Radio Wave Propagation (RWP). IEEE, 2019. http://dx.doi.org/10.1109/rwp.2019.8810392.

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Ivanova, V. A., V. I. Kurkin e V. A. Ivanov. "Peculiarities of the HF radio wave propagation over round-the-world paths". In IET 11th International Conference on Ionospheric Radio Systems and Techniques (IRST 2009). IEE, 2009. http://dx.doi.org/10.1049/cp.2009.0081.

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Khristoforov, Stanislav, e Vladimir Bochkarev. "Estimation of Geomagnetic and Solar Indices by Global Ionospheric Maps With Use of Neural Networks". In 2019 Russian Open Conference on Radio Wave Propagation (RWP). IEEE, 2019. http://dx.doi.org/10.1109/rwp.2019.8810207.

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Nguyen, Bach T., e Jamesina J. Simpson. "A stochastic FDTD model of electromagnetic wave propagation in magnetized ionospheric plasma". In 2013 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium). IEEE, 2013. http://dx.doi.org/10.1109/usnc-ursi.2013.6715363.

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Rapporti di organizzazioni sul tema "Ionospheric radio wave propagation"

Tawk, Youssef, e Christopher Romero. Millimeter Wave Radio Frequency Propagation Model Development. Fort Belvoir, VA: Defense Technical Information Center, agosto 2014. http://dx.doi.org/10.21236/ada609960.

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Kersley, L., S. E. Pryse e N. S. Wheadon. Radio-Wave Scintillations and Ionospheric Irregularities at High Latitudes. Fort Belvoir, VA: Defense Technical Information Center, maggio 1987. http://dx.doi.org/10.21236/ada192140.

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Argo, P. E., D. DeLapp, C. D. Sutherland e R. G. Farrer. Tracker: A three-dimensional raytracing program for ionospheric radio propagation. Office of Scientific and Technical Information (OSTI), dicembre 1994. http://dx.doi.org/10.2172/10196580.

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Barrios, A. E. Radio Wave Propagation in Horizontally Inhomogeneous Environments by Using the Parabolic Equation Method. Fort Belvoir, VA: Defense Technical Information Center, maggio 1991. http://dx.doi.org/10.21236/ada242082.

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Heinz, Brian J., David Richie, Song J. Park e Dale R. Shires. Real-Time Radio Wave Propagation for Mobile Ad-Hoc Network Emulation and Simulation Using General Purpose Graphics Processing Units (GPGPUs). Fort Belvoir, VA: Defense Technical Information Center, maggio 2014. http://dx.doi.org/10.21236/ada601670.

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