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1
Walker, I. K., J. A. T. Heaton, L. Kersley, C. N. Mitchell, S. E. Pryse, and M. J. Williams. "EISCAT verification in the development of ionospheric tomography." Annales Geophysicae 14, no. 12 (December 31, 1996): 1413–21. http://dx.doi.org/10.1007/s00585-996-1413-8.
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Abstract. This paper highlights the important role played by the EISCAT radar for verification in the development of tomographic techniques to produce images of ionospheric electron density. A brief review is given of some of the stages in the application of tomographic reconstruction techniques to the ionosphere. Results are presented to illustrate the effectiveness of the method in imaging ionospheric structures at high latitudes. In addition, the results include the first tomographic image of the ionosphere for a region extending from mid-latitudes over mainland Scandinavia to high latitudes above Svalbard.
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Prajapati, Parinda, and Nimisha Patel. "Ionospheric Model Development for Indian Region: A Survey Paper." ECS Transactions 107, no. 1 (April 24, 2022): 11075–82. http://dx.doi.org/10.1149/10701.11075ecst.
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Ionosphere’s role is most important in vigorous satellite communication for the navigation positional correctness purpose. Ionosphere contains diverse layers reliant on its electron density with altitude in the layer. There are various ionospheric models to forecast electron density with temporal resolutions cited by literatures. GPS data is frequently used by these models. So, the necessity is a prerequisite of evolving ionospheric models with different time duration for low latitudes of India. Also, an ionosphere tomography is considered as an ill-posed problem. Ionospheric TEC found simultaneously at numerous locations can be preserved with several algorithms to conquer electron density. This research is proposed for evolving a model to forecast 3D tomography of total electron density for the whole Indian region. Mainly used satellite data can be collected by various means. The management of vast statistics are planned by using data mining techniques and artificial neural network techniques for estimation. This paper is an outcome of detailed research on ionospheric model development.
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Jin, Shuanggen, J. U. Park, J. L. Wang, B. K. Choi, and P. H. Park. "Electron Density Profiles Derived From Ground-Based GPS Observations." Journal of Navigation 59, no. 3 (August 23, 2006): 395–401. http://dx.doi.org/10.1017/s0373463306003821.
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Nowadays GPS is widely used to monitor the ionosphere. However, the current results from ground-based GPS observations only provide some information on the horizontal structure of the ionosphere, and are extremely restricted in mapping its vertical structure. In this paper, tomography reconstruction technique was used to image 3D ionospheric structure with ground-based GPS. The first result of the 3D images of the ionospheric electron density distribution in South Korea has been generated from the permanent Korean GPS Network (KGN) data. Compared with the profiles obtained by independent ionosondes at or near the GPS receiver stations, the electron density profiles obtained by the GPS tomographic construction method are in better agreement, showing the validity of the GPS ionospheric tomographic reconstruction. It has also indicated that GPS-based 3D ionospheric mapping has the potential to complement other expensive observing techniques in ionospheric mapping, such as ionosondes and radar.
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Bae, Tae-Suk, and Minho Kim. "Performance Analysis of Network-RTK Techniques for Drone Navigation considering Ionospheric Conditions." Journal of Sensors 2018 (2018): 1–8. http://dx.doi.org/10.1155/2018/5154697.
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Recently, an accurate positioning has become the kernel of autonomous navigation with the rapid growth of drones including mapping purpose. The Network-based Real-time Kinematic (NRTK) system was predominantly used for precision positioning in many fields such as surveying and agriculture, mostly in static mode or low-speed operation. The NRTK positioning, in general, shows much better performance with the fixed integer ambiguities. However, the success rate of the ambiguity resolution is highly dependent on the ionospheric condition and the surrounding environment of Global Navigation Satellite System (GNSS) positioning, which particularly corresponds to the low-cost GNSS receivers. We analyzed the effects of the ionospheric conditions on the GNSS NRTK, as well as the possibility of applying the mobile NRTK to drone navigation for mapping. Two NRTK systems in operation were analyzed during a period of high ionospheric conditions, and the accuracy and the performance were compared for several operational cases. The test results show that a submeter accuracy is available even with float ambiguity under a favorable condition (i.e., visibility of the satellites as well as stable ionosphere). We still need to consider how to deal with ionospheric disturbances which may prevent NRTK positioning.
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Amm, O., A. Aruliah, S. C. Buchert, R. Fujii, J. W. Gjerloev, A. Ieda, T. Matsuo, C. Stolle, H. Vanhamäki, and A. Yoshikawa. "Towards understanding the electrodynamics of the 3-dimensional high-latitude ionosphere: present and future." Annales Geophysicae 26, no. 12 (December 5, 2008): 3913–32. http://dx.doi.org/10.5194/angeo-26-3913-2008.
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Abstract. Traditionally, due to observational constraints, ionospheric modelling and data analysis techniques have been devised either in one dimension (e.g. along a single radar beam), or in two dimensions (e.g. over a network of magnetometers). With new upcoming missions like the Swarm ionospheric multi-satellite project, or the EISCAT 3-D project, the time has come to take into account variations in all three dimensions simultaneously, as they occur in the real ionosphere. The link between ionospheric electrodynamics and the neutral atmosphere circulation which has gained increasing interest in the recent years also intrinsically requires a truly 3-dimensional (3-D) description. In this paper, we identify five major science questions that need to be addressed by 3-D ionospheric modelling and data analysis. We briefly review what proceedings in the young field of 3-D ionospheric electrodynamics have been made in the past to address these selected question, and we outline how these issues can be addressed in the future with additional observations and/or improved data analysis and simulation techniques. Throughout the paper, we limit the discussion to high-latitude and mesoscale ionospheric electrodynamics, and to directly data-driven (not statistical) data analysis.
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Hughes, J. M., W. A. Bristow, R. A. Greenwald, and R. J. Barnes. "Determining characteristics of HF communications links using SuperDARN." Annales Geophysicae 20, no. 7 (July 31, 2002): 1023–30. http://dx.doi.org/10.5194/angeo-20-1023-2002.
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Abstract. Space weather effects can strongly influence high-frequency (HF) communications by changing the ionospheric environment through which the radio waves propagate. Since many systems utilize HF communications, the ability to make real-time assessments of propagation conditions is an important part of space weather monitoring systems. In this paper, we present new techniques for measuring high-latitude HF communications link parameters using data from SuperDARN radars. These techniques use ground-scatter returns to define the variation in skip distance with frequency. From these data, the maximum usable frequency (MUF) as a function of range is determined and ionospheric critical frequencies are estimated. These calculations are made in near-real-time and the results are made available on the World Wide Web. F-region critical frequencies calculated using this method show good agreement with ionosonde data.Key words. Ionosphere (active experiments; instruments and techniques) – Radio science (ionospheric propagation)
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Chan, A. H. Y., and P. S. Cannon. "Nonlinear forecasts of ƒ<i>o</i>F2: variation of model predictive accuracy over time." Annales Geophysicae 20, no. 7 (July 31, 2002): 1031–38. http://dx.doi.org/10.5194/angeo-20-1031-2002.
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Abstract. Space weather effects can strongly influence high-frequency (HF) communications by changing the ionospheric environment through which the radio waves propagate. Since many systems utilize HF communications, the ability to make real-time assessments of propagation conditions is an important part of space weather monitoring systems. In this paper, we present new techniques for measuring high-latitude HF communications link parameters using data from SuperDARN radars. These techniques use ground-scatter returns to define the variation in skip distance with frequency. From these data, the maximum usable frequency (MUF) as a function of range is determined and ionospheric critical frequencies are estimated. These calculations are made in near-real-time and the results are made available on the World Wide Web. F-region critical frequencies calculated using this method show good agreement with ionosonde data.Key words. Ionosphere (active experiments; instruments and techniques) – Radio science (ionospheric propagation)
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Pimenta, A. A., P. R. Fagundes, Y. Sahai, J. A. Bittencourt, and J. R. Abalde. "Equatorial F-region plasma depletion drifts: latitudinal and seasonal variations." Annales Geophysicae 21, no. 12 (December 31, 2003): 2315–22. http://dx.doi.org/10.5194/angeo-21-2315-2003.
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Abstract. The equatorial ionospheric irregularities have been observed in the past few years by different techniques (e.g. ground-based radar, digisonde, GPS, optical instruments, in situ satellite and rocket instrumentation), and its time evolution and propagation characteristics can be used to study important aspects of ionospheric dynamics and thermosphere-ionosphere coupling. At present, one of the most powerful optical techniques to study the large-scale ionospheric irregularities is the all-sky imaging photometer system, which normally measures the strong F-region nightglow 630 nm emission from atomic oxygen. The monochromatic OI 630 nm emission images usually show quasi-north-south magnetic field-aligned intensity depletion bands, which are the bottomside optical signatures of large-scale F-region plasma irregularities (also called plasma bubbles). The zonal drift velocities of the plasma bubbles can be inferred from the space-time displacement of the dark structures (low intensity regions) seen on the images. In this study, images obtained with an all-sky imaging photometer, using the OI 630 nm nightglow emission, from Cachoeira Paulista (22.7° S, 45° W, 15.8° S dip latitude), Brazil, have been used to determine the nocturnal monthly and latitudinal variation characteristics of the zonal plasma bubble drift velocities in the low latitude (16.7° S to 28.7° S) region. The east and west walls of the plasma bubble show a different evolution with time. The method used here is based on the western wall of the bubble, which presents a more stable behavior. Also, the observed zonal plasma bubble drift velocities are compared with the thermospheric zonal neutral wind velocities obtained from the HWM-90 model (Hedin et al., 1991) to investigate the thermosphere-ionosphere coupling. Salient features from this study are presented and discussed.Key words. Ionosphere (ionosphere-atmosphere interactions; ionospheric irregularities; instruments and techniques)
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Provan, G., T. K. Yeoman, S. E. Milan, J. M. Ruohoniemi, and R. Barnes. "An assessment of the "map-potential" and "beam-swinging" techniques for measuring the ionospheric convection pattern using data from the SuperDARN radars." Annales Geophysicae 20, no. 2 (February 28, 2002): 191–202. http://dx.doi.org/10.5194/angeo-20-191-2002.
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Abstract. The SuperDARN HF coherent scatter radars (Greenwald et al., 1995) provide line-of-sight (l-o-s) velocity measurements of ionospheric convection flow over the polar regions of the northern and southern hemispheres. A number of techniques have been developed in order to obtain 2-D plasma flow vectors from these l-o-s observations. This study entails a comparison of the ionospheric flow vectors derived using the "map-potential", and "beam-swinging" techniques with the vectors derived using the "merging" technique. The merging technique is assumed to be the most accurate method of deriving local flow vectors from l-o-s velocities. We can conclude that the map-potential model is significantly more successful than the beam-swinging technique at estimating both the magnitude and the direction of the large-scale ionospheric convection flow vectors. The quality of the fit is dependent on time of day, with vectors observed at low latitudes in the dawn sector agreeing most closely with the merged vector flow pattern.Key words. Ionosphere (plasma convection; instruments and techniques) – Radio science (instruments and techniques)
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Le Roux, Y. M., J. Ménard, J. P. Jolivet, and P. J. Davy. "<i>Letter to the Editor:</i> SCIPION, a new flexible ionospheric sounder in Senegal." Annales Geophysicae 16, no. 6 (June 30, 1998): 738–42. http://dx.doi.org/10.1007/s00585-998-0738-x.
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Abstract. SCIPION is a new state of the art digital sounder that has been devoloped by France Telecom-CNET for ionospheric monitoring and research. Extensive data processing using DSP technology has resulted in a low power, low cost and full featured system for both vertical and oblique soundings. A SCIPION system is in the process of being installed in Dakar, Senegal, to study HF propagation in the sub-equatorial ionosphere. However, preliminary results have still been obtained during experiments wit a prototype system. In this paper, the system is described and some illustrative examples of its capabilities are shown.Keywords. Ionosphere (Equatorial ionosphere, Instruments and Techniques) &#x22C5 Radio science (ionospheric propagation).
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Jarmołowski, Wojciech, Anna Belehaki, Manuel Hernández Pajares, Michael Schmidt, Andreas Goss, Paweł Wielgosz, Heng Yang, et al. "Combining Swarm Langmuir probe observations, LEO-POD-based and ground-based GNSS receivers and ionosondes for prompt detection of ionospheric earthquake and tsunami signatures: case study of 2015 Chile-Illapel event." Journal of Space Weather and Space Climate 11 (2021): 58. http://dx.doi.org/10.1051/swsc/2021042.
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The study investigates ionospheric electric field responses to the earthquake (EQ) of magnitude 8.3, and the related seismic activity and tsunami triggered by the mainshock in Chile-Illapel region, at 22:54 UTC, in the evening of September 16, 2015. The work is a wider review of available ground and satellite data and techniques available to detect seismically induced traveling ionospheric disturbances (TID) and irregularities of smaller scale. The data used in the experiment includes several types of ground and satellite observations from low-Earth orbit (LEO) satellites. The number of techniques applied here is also extended and includes spectral analysis of LEO along-track data and composed analysis of ground GNSS data. The timeframe of the analyses is focused on September 16 and 17, 2015 but also extended to several adjacent days, where an enhanced seismic activity has been recorded. Several examples of seismically triggered TIDs are shown, as detected by combined observations from more than one source and applying different methods, including spectral analysis. These disturbances occur before the mainshock, just after, or in time following this large EQ, and can be found in close neighborhood of Chile-Illapel or far away from the epicenter. The objective of the work was to demonstrate an increasing number of available data and techniques, which can be limited when applied alone, but their combination can provide many advantages in the analysis of seismically disturbed ionosphere. The combination of LEO satellite data reaching all regions of the globe with local but dense ground-based GNSS data and ionospheric HF sounders looks promising, especially in view of the nearby availability of CubeSat constellations equipped with instruments for ionosphere sounding. An important conclusion coming from the study is a need for spectral analysis techniques in the processing of LEO along-track data and the requirement of the validation of LEO observations with separate LEO data or ground-based data. A general but key finding refers to the complementarities of different observations of the ionospheric electric field, which is critically important in the case of analyzing ionospheric irregularities in the extended and composed ionosphere, especially if not every sounding direction can successfully find it.
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Savastano, Giorgio, Attila Komjathy, Esayas Shume, Panagiotis Vergados, Michela Ravanelli, Olga Verkhoglyadova, Xing Meng, and Mattia Crespi. "Advantages of Geostationary Satellites for Ionospheric Anomaly Studies: Ionospheric Plasma Depletion Following a Rocket Launch." Remote Sensing 11, no. 14 (July 23, 2019): 1734. http://dx.doi.org/10.3390/rs11141734.
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In this study, we analyzed signals transmitted by the U.S. Wide Area Augmentation System (WAAS) geostationary (GEO) satellites using the Variometric Approach for Real-Time Ionosphere Observation (VARION) algorithm in a simulated real-time scenario, to characterize the ionospheric response to the 24 August 2017 Falcon 9 rocket launch from Vandenberg Air Force Base in California. VARION is a real-time Global Navigation Satellites Systems (GNSS)-based algorithm that can be used to detect various ionospheric disturbances associated with natural hazards, such as tsunamis and earthquakes. A noise reduction algorithm was applied to the VARION-GEO solutions to remove the satellite-dependent noise term. Our analysis showed that the interactions of the exhaust plume with the ionospheric plasma depleted the total electron content (TEC) to a level comparable with nighttime TEC values. During this event, the geometry of the satellite-receiver link is such that GEO satellites measured the depleted plasma hole before any GPS satellites. We estimated that the ionosphere relaxed back to a pre-perturbed state after about 3 h, and the hole propagated with a mean speed of about 600 m/s over a region of 700 km in radius. We conclude that the VARION-GEO approach can provide important ionospheric TEC real-time measurements, which are not affected by the motion of the ionospheric pierce points (IPPs). Furthermore, the VARION-GEO measurements experience a steady noise level throughout the entire observation period, making this technique particularly useful to augment and enhance the capabilities of well-established GNSS-based ionosphere remote sensing techniques and future ionospheric-based early warning systems.
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Smith, N. D., D. Pokhotelov, C. N. Mitchell, and C. J. Budd. "Image-model coupling: application to an ionospheric storm." Nonlinear Processes in Geophysics 17, no. 4 (August 20, 2010): 361–69. http://dx.doi.org/10.5194/npg-17-361-2010.
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Abstract. Techniques such as tomographic reconstruction may be used to provide images of electron content in the ionosphere. Models are also available which attempt to describe the dominant physical processes operating in the ionosphere, or the statistical relationships between ionospheric variables. It is sensible to try and couple model output to tomographic images with the aim of inferring the values of driver variables which best replicate some description of electron content imaged in the ionosphere, according to some criterion. This is a challenging task. The following describes an attempt to couple an ionospheric model to a tomographic reconstruction of the geomagnetic storm of 20 November 2003, along a latitudal line segment above north America. A simple model was chosen to reduce the number of input drivers that were varied. The investigation illustrates some of the issues involved in image-model coupling. The ability to make scientific deductions depends on the accuracy of the assumptions in the ionospheric model and the accuracy of the tomographic reconstruction. An ensemble technique was used to help assess confidence in the reconstruction.
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Pryse, S. E., L. Kersley, M. J. Williams, and I. K. Walker. "The spatial structure of the dayside ionospheric trough." Annales Geophysicae 16, no. 10 (October 31, 1998): 1169–79. http://dx.doi.org/10.1007/s00585-998-1169-4.
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Abstract. Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polar-cap convection.Key words. Ionosphere-magnetosphere interactions · Polar ionosphere · Radio science · Ionospheric propagation
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Bhattacharyya, Archana. "Equatorial Plasma Bubbles: A Review." Atmosphere 13, no. 10 (October 8, 2022): 1637. http://dx.doi.org/10.3390/atmos13101637.
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The equatorial plasma bubble (EPB) phenomenon is an important component of space weather as the ionospheric irregularities that develop within EPBs can have major detrimental effects on the operation of satellite-based communication and navigation systems. Although the name suggests that EPBs occur in the equatorial ionosphere, the nature of the plasma instability that gives rise to EPBs is such that the bubbles may extend over a large part of the global ionosphere between geomagnetic latitudes of approximately ±15°. The scientific challenge continues to be to understand the day-to-day variability in the occurrence and characteristics of EPBs, such as their latitudinal extent and the development of irregularities within EPBs. In this paper, basic theoretical aspects of the plasma processes involved in the generation of EPBs, associated ionospheric irregularities, and observations of their characteristics using different techniques will be reviewed. Special focus will be given to observations of scintillations produced by the scattering of VHF and higher frequency radio waves while they propagate through ionospheric irregularities associated with EPBs, as these observations have revealed new information about the non-linear development of Rayleigh–Taylor instability in equatorial ionospheric plasma, which is the genesis of EPBs.
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de Villiers, J. S., and P. J. Cilliers. "Applying inversion techniques to derive source currents and geoelectric fields for geomagnetically induced current calculations." Annales Geophysicae 32, no. 10 (October 16, 2014): 1263–75. http://dx.doi.org/10.5194/angeo-32-1263-2014.
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Abstract. This research focuses on the inversion of geomagnetic variation field measurement to obtain source currents in the ionosphere. During a geomagnetic disturbance, the ionospheric currents create magnetic field variations that induce geoelectric fields, which drive geomagnetically induced currents (GIC) in power systems. These GIC may disturb the operation of power systems and cause damage to grounded power transformers. The geoelectric fields at any location of interest can be determined from the source currents in the ionosphere through a solution of the forward problem. Line currents running east–west along given surface position are postulated to exist at a certain height above the Earth's surface. This physical arrangement results in the fields on the ground having the magnetic north and down components, and the electric east component. Ionospheric currents are modelled by inverting Fourier integrals (over the wavenumber) of elementary geomagnetic fields using the Levenberg–Marquardt technique. The output parameters of the inversion model are the current strength, height and surface position of the ionospheric current system. A ground conductivity structure with five layers from Quebec, Canada, based on the Layered-Earth model is used to obtain the complex skin depth at a given angular frequency. This paper presents preliminary and inversion results based on these structures and simulated geomagnetic fields. The results show some interesting features in the frequency domain. Model parameters obtained through inversion are within 2% of simulated values. This technique has applications for modelling the currents of electrojets at the equator and auroral regions, as well as currents in the magnetosphere.
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Ning, Yafei, and Jun Tang. "Study of ionospheric disturbances over the China mid- and low-latitude region with GPS observations." Annales Geophysicae 36, no. 1 (January 22, 2018): 81–89. http://dx.doi.org/10.5194/angeo-36-81-2018.
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Abstract. Ionospheric disturbances constitute the main restriction factor for precise positioning techniques based on global positioning system (GPS) measurements. Simultaneously, GPS observations are widely used to determine ionospheric disturbances with total electron content (TEC). In this paper, we present an analysis of ionospheric disturbances over China mid- and low-latitude area before and during the magnetic storm on 17 March 2015. The work analyses the variation of magnetic indices, the amplitude of ionospheric irregularities observed with four arrays of GPS stations and the influence of geomagnetic storm on GPS positioning. The results show that significant ionospheric TEC disturbances occurred between 10:30 and 12:00 UT during the main phase of the large storm, and the static position reliability for this period are little affected by these disturbances. It is observed that the positive and negative disturbances propagate southward along the meridian from mid-latitude to low-latitude regions. The propagation velocity is from about 200 to 700 m s−1 and the amplitude of ionospheric disturbances is from about 0.2 to 0.9 TECU min−1. Moreover, the position dilution of precession (PDOP) with static precise point positioning (PPP) on storm and quiet days is 1.8 and 0.9 cm, respectively. This study is based on the analysis of ionospheric variability with differential rate of vertical TEC (DROVT) and impact of ionospheric storm on positioning with technique of GPS PPP. Keywords. Ionosphere (ionospheric disturbances)
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Prol, Fabricio Dos Santos, and Paulo De Oliveira Camargo. "REVIEW OF TOMOGRAPHIC RECONSTRUCTION METHODS OF THE IONOSPHERE USING GNSS." Revista Brasileira de Geofísica 33, no. 3 (July 27, 2015): 445. http://dx.doi.org/10.22564/rbgf.v33i3.947.
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ABSTRACT. Spatial and temporal variation of the electron density in the atmosphere makes the ionosphere a difficult region to model. A major difficulty arises due to the incomplete geometrical coverage of the Global Navigation Satellite System (GNSS) for tomographic applications, making the ionospheric tomographic system an ill-conditioned problem. Although the tomographic system is ill-conditioned, several techniques have been developed to partially overcome the problem. There is great interest in using tomographic techniques for ionospheric imaging, because it allows describing the ionosphere in terms of electron density, which is an important parameter for studying the behavior of the physical processes that occur in the upper atmosphere. In Brazil, there are additional interests in the tomographic techniques, due to the peculiar characteristics of the ionosphere and of the geomagnetic field over the region. In this direction, methods of ionospheric tomographic reconstruction are presented and discussed in this review. Particular emphasis is given to the mathematical formulation from grid-based and function-based methods and are presented some of their main advantages and limitations.Keywords: TEC, Inverse Problem, Grid-Based Tomography, Function-Based Tomography, Ionospheric Imaging. RESUMO. A variação espaço-temporal da densidade eletrônica na atmosfera terrestre torna a ionosfera uma região de difícil modelagem. A principal dificuldade no imageamento da ionosfera com o GNSS (Global Navigation Satellite System ) é devido à geometria dos satélites, pois torna o sistema tomográfico mal condicionado. Muito embora a geometria não permita solução direta do sistema, diversas técnicas foram desenvolvidas para parcialmente superar tal problema. Há grande interesse no uso de técnicas de tomografia para o imageamento da ionosfera, pois permitem descrever a ionosfera ao nível da densidade eletrônica, sendo este um importante parâmetro para compreender os processos físicos que ocorrem na alta atmosfera. No Brasil, existem interesses adicionais no imageamento ionosférico por meio de técnicas tomográficas devido às características peculiares da ionosfera e do campo geomagnético sobre a região. Neste sentido, métodos utilizados para a reconstrução tomográfica da ionosfera são apresentados e discutidos nesta revisão. Uma ênfase especial é dada para a formulação matemática dos métodos baseados em células e em funções, além da apresentação de algumas de suas principais vantagens e limitações.Palavras-chave: TEC, Problema Inverso, Tomografia Baseada em Células, Tomografia Baseada em Funções, Imageamento Ionosférico.
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Heaton, J. A. T., G. O. L. Jones, and L. Kersley. "Toward ionospheric tomography in Antarctica: first steps and comparison with dynasonde observations." Antarctic Science 8, no. 3 (September 1996): 297–302. http://dx.doi.org/10.1017/s0954102096000430.
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Total electron content (TEC) measurements obtained at two Antarctic stations over nine months beginning early in 1994 have been analysed as a first step to performing ionospheric tomography. Two receiving systems were deployed at the Faraday and Halley research stations operated by the British Antarctic Survey to monitor signals from a random selection of passes of satellites in the Navy Navigational Satellite System. The resultant measurements of total electron content have been inverted and combined with ionosonde measurements of true height and foF2 to yield two-dimensional contour maps of ionospheric electron density. In spite of the poor geometry of the observations, some 130 satellite passes were found to be suitable for reconstruction using the techniques developed for ionospheric tomography. The contour maps of plasma density have been compared with independent observations of the vertical electron density profile measured by the dynasonde ionospheric sounder located at Halley. An example is presented of a deep trough investigated by the technique, illustrating the potential of the tomographic method for study of an extended spatial region of the ionosphere over inhospitable terrain.
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Samardjiev, T., P. A. Bradley, Lj R. Cander, and M. I. Dick. "Ionospheric mapping by computer contouring techniques." Electronics Letters 29, no. 20 (1993): 1794. http://dx.doi.org/10.1049/el:19931194.
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André, R., M. Pinnock, J. P. Villain, and C. Hanuise. "Influence of magnetospheric processes on winter HF radar spectra characteristics." Annales Geophysicae 20, no. 11 (November 30, 2002): 1783–93. http://dx.doi.org/10.5194/angeo-20-1783-2002.
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Abstract. This study investigates further the relationship between regions of the magnetosphere and the characteristics of HF radar Doppler spectra recorded in the ionospheric projection of those regions. It builds on earlier work, which has reported a relationship between the Doppler spectral width and the ionospheric projection of the magnetospheric cusp region, by introducing novel techniques for classifying the Doppler spectra recorded by the SuperDARN radars. We first review the geophysical factors that can condition the characteristics of the autocorrelation function (ACF) data produced by the radars. This leads to a classification scheme of the ACF data which is then applied to a large database compiled from winter data taken by the Northern Hemisphere Super-DARN radars. This statistical study shows that the ACF characteristics are not randomly distributed in space, but rather are spatially organized in the ionosphere. This paper suggests that these regions are ordered primarily by the low energy (<approx> 1 keV) electron precipitation region and the presence of intense ULF wave activity.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; plasma convection)
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Altadill, David, Antoni Segarra, Estefania Blanch, José Miguel Juan, Vadym V. Paznukhov, Dalia Buresova, Ivan Galkin, Bodo W. Reinisch, and Anna Belehaki. "A method for real-time identification and tracking of traveling ionospheric disturbances using ionosonde data: first results." Journal of Space Weather and Space Climate 10 (2020): 2. http://dx.doi.org/10.1051/swsc/2019042.
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Traveling Ionospheric Disturbances (TIDs) are wave-like propagating irregularities that alter the electron density environment and play an important role spreading radio signals propagating through the ionosphere. A method combining spectral analysis and cross-correlation is applied to time series of ionospheric characteristics (i.e., MUF(3000)F2 or foF2) using data of the networks of ionosondes in Europe and South Africa to estimate the period, amplitude, velocity and direction of propagation of TIDs. The method is verified using synthetic data and is validated through comparison of TID detection results made with independent observational techniques. The method provides near real time capability of detection and tracking of Large-Scale TIDs (LSTIDs), usually associated with auroral activity.
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Захаров, Виктор, Viktor Zakharov, Вячеслав Пилипенко, Vyacheslav Pilipenko, Валерий Грушин, Valeriy Grushin, Аскар Хамидуллин, and Askar Khamidullin. "Impact of typhoon Vongfong 2014 on the ionosphere and geomagnetic field according to Swarm satellite data: 1. Wave disturbances of ionospheric plasma." Solar-Terrestrial Physics 5, no. 2 (June 28, 2019): 101–8. http://dx.doi.org/10.12737/stp-52201914.
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The article considers the influence of large atmospheric processes on the ionosphere by the example of tropical typhoon Vongfong 2014. We use data obtained from three SWARM satellite missions (450–500 km altitude). We discuss two possible mechanisms of transfer of atmospheric disturbances to ionospheric heights. The first mechanism is the generation of acoustic-gravity waves (AGWs); the second mechanism considers the excitation of electric fields in the atmosphere. We propose new techniques for detecting the ionospheric response to AGW, which rely on low-orbit satellite data. The first technique is based on determination of relative electron density variations in the frequency band from 15 to 150–180 s, corresponding to certain scales of AGW. The second technique estimates space-time derivatives of the electron density, measured by two nearby SWARM satellites. We present and estimate the characteristic magnitudes of ionospheric response effects, their localization and spatial-temporal characteristics for the large tropical cyclone under study.
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Захаров, Виктор, Viktor Zakharov, Вячеслав Пилипенко, Vyacheslav Pilipenko, Валерий Грушин, Valeriy Grushin, Аскар Хамидуллин, and Askar Khamidullin. "Impact of typhoon Vongfong 2014 on the ionosphere and geomagnetic field according to Swarm satellite data: 1. Wave disturbances of ionospheric plasma." Solnechno-Zemnaya Fizika 5, no. 2 (June 28, 2019): 114–23. http://dx.doi.org/10.12737/szf-52201914.
Full textAbstract:
The article considers the influence of large atmospheric processes on the ionosphere by the example of tropical typhoon Vongfong 2014. We use data obtained from three SWARM satellite missions (450–500 km altitude). We discuss two possible mechanisms of transfer of atmospheric disturbances to ionospheric heights. The first mechanism is the generation of acoustic-gravity waves (AGWs); the second mechanism considers the excitation of electric fields in the atmosphere. We propose new techniques for detecting the ionospheric response to AGW, which rely on low-orbit satellite data. The first technique is based on determination of relative electron density variations in the frequency band from 15 to 150–180 s, corresponding to certain scales of AGW. The second technique estimates space-time derivatives of the electron density, measured by two nearby SWARM satellites. We present and estimate the characteristic magnitudes of ionospheric response effects, their localization and spatial-temporal characteristics for the large tropical cyclone under study.
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Angrisano, Antonio, Salvatore Gaglione, Ciro Gioia, Marco Massaro, and Salvatore Troisi. "Benefit of the NeQuick Galileo Version in GNSS Single-Point Positioning." International Journal of Navigation and Observation 2013 (November 27, 2013): 1–11. http://dx.doi.org/10.1155/2013/302947.
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The GNSS measurements are strongly affected by ionospheric effects, due to the signal propagation through ionosphere; these effects could severely degrade the position; hence, a model to limit or remove the ionospheric error is necessary. The use of several techniques (DGPS, SBAS, and GBAS) reduces the ionospheric effect, but implies the use of expensive devices and/or complex architectures necessary to meet strong requirements in terms of accuracy and reliability for safety critical application. The cheapest and most widespread GNSS devices are single frequency stand-alone receivers able to partially correct this kind of error using suitable models. These algorithms compute the ionospheric delay starting from ionospheric model, which uses parameters broadcast within the navigation messages. NeQuick is a three-dimensional and time-dependent ionospheric model adopted by Galileo, the European GNSS, and developed by International Centre for Theoretical Physics (ICTP) together with Institute for Geophysics, Astrophysics, and Meteorology of the University of Graz. The aim of this paper is the performance assessment in single point positioning of the NeQuick Galileo version provided by ESA and the comparison with respect to the Klobuchar model used for GPS; the analysis is performed in position domain and the errors are examined in terms of RMS and maximum error for the horizontal and vertical components. A deep analysis is also provided for the application of the exanimated model in the first possible Galileo only position fix.
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Shi, Liu, Guo, Liu, You, and Wang. "Pre-Earthquake and Coseismic Ionosphere Disturbances of the Mw 6.6 Lushan Earthquake on 20 April 2013 Monitored by CMONOC." Atmosphere 10, no. 4 (April 22, 2019): 216. http://dx.doi.org/10.3390/atmos10040216.
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In order to study the coupling relationship between large earthquakes and the ionosphere, the techniques of ionosphere data acquisition were refined by the Crustal Movement Observation Network of China (CMONOC) to detect the pre-earthquake ionospheric abnormal and coseismic ionospheric disturbances (CID) of the Mw 6.6 Lushan earthquake on 20 April 2013. Based on the regional ionosphere maps (RIMs) derived from the Global Positioning System (GPS) observations of CMONOC, the ionospheric local effects near the epicenter of the Lushan earthquake one month prior to the shock were analyzed. The results show that the total electron content (TEC) anomalies appeared 12–14 (6–8 April), 19 (1 April), and 25–27 (24–26 March) days prior to the Lushan earthquake, which are defined as periods 1, 2, and 3, respectively. Multi-indices including the ring current index (Dst), geomagnetic planetary (Kp) index, wind plasma speed (Vsw) index, F10.7, and solar flares were utilized to represent the solar–terrestrial environment in different scales and eliminate the effects of solar and geomagnetic activities on the ionosphere. After the interference of solar–terrestrial activity and the diurnal variation in the lower thermosphere were excluded, the TEC variations with obvious equatorial ionospheric anomaly (EIA) in period-1 were considered to be related to the Lushan earthquake. We further retrieved precise slant TECs (STECs) near the epicenter to study the coseismic ionospheric disturbance (CID). The results show that there was clear STEC disturbance occurring within half an hour after the Lushan earthquake, and the CID propagation distance was less than the impact radius of the Lushan earthquake (689 km). The shell models with different altitudes were adopted to analyze the propagation speed of the CID. It is found that at the F2-layer with the altitude of 277 km, which had a CID horizontal propagation velocity of 0.84 ± 0.03 km/s, was in accordance with the acoustic wave propagation velocity. The calculated velocity acoustic wave from the epicenter to the ionospheric pierce points of this shell model was about 0.53 ± 0.03km/s, which was also consistent with its actual velocity within the altitude of 0–277 km. Affected by the geomagnetic field, the CID mainly propagated along the southeast direction at the azimuth of 190°, which was almost parallel to the local magnetic line.
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Amm, O. "Method of characteristics in spherical geometry applied to a Harang-discontinuity situation." Annales Geophysicae 16, no. 4 (April 30, 1998): 413–24. http://dx.doi.org/10.1007/s00585-998-0413-2.
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Abstract. The method of characteristics for obtaining spatial distributions of ionospheric electrodynamic parameters from ground-based spatial observations of the ground magnetic disturbance and the ionospheric electric field is presented in spherical geometry. The method includes tools for separation of the external magnetic disturbance, its continuation to the ionosphere, and calculation of ionospheric equivalent currents. Based on these and the measured electric field distribution, the ionospheric Hall conductance is calculated as the primary output of the method. By estimating the Hall- to-Pedersen conductance ratio distribution, the remaining ionospheric electrodynamic parameters are inferred. The method does not assume ∇×E=0 to allow to study time-dependent situations. The application of this method to a Harang discontinuity (HD) situation on 27 October 1977, 17:39 UT, reveals the following: (1) The conductances at and north of the HD are clearly reduced as compared to the eastern electrojet region. (2) Plasma flow across the HD is observed, but almost all horizontal current is diverted into upward-flowing field-aligned currents (FACs) there. (3) The FACs connected to the Hall currents form a latitudinally aligned sheet with a magnitude peak between the electrically and magnetically defined HD, where break-up arcs are often observed. Their magnitude is larger than that of the more uniformly distributed FACs connected to the Pedersen currents. They also cause the southward shift of the magnetically defined HD with respect to the electrically defined one. (4) A tilt of the HD with respect to geomagnetic latitude as proposed by an earlier study on the same event, which used composite vector plot technique, and by statistical studies, is not observed in our single time-step analysis.Key words. Ionosphere · Electric fields and currents · Instruments and techniques · Magnetospheric physics · Current systems
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Seema, C. S., and P. R. Prince. "Phase analysis of solar activity indices using wavelet techniques." Proceedings of the International Astronomical Union 13, S340 (February 2018): 165–66. http://dx.doi.org/10.1017/s1743921318001266.
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AbstractA precise knowledge of solar extreme ultraviolet (EUV) irradiance is of great importance for better understanding of Earth′s ionosphere and thermosphere. The search for an ideal solar EUV proxy is vital since the ionospheric and thermospheric models are based on the solar proxies of EUV radiation. In this study, the phase asynchrony analysis of solar EUV data with other solar activity indices during solar cycle 23 is done. The cross-wavelet transform (XWT) technique is used to reveal the phase difference between the two time series of solar indices. Analysis reveals that the phase relationship between the indices is both time and frequency dependent. The solar indices F10.7 and Mg II core-to-wing index are found to be more synchronous with solar EUV data for low frequency components.
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Hocke, K., and K. Schlegel. "A review of atmospheric gravity waves and travelling ionospheric disturbances: 1982-1995." Annales Geophysicae 14, no. 9 (September 30, 1996): 917–40. http://dx.doi.org/10.1007/s00585-996-0917-6.
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Abstract. Recent investigations of atmospheric gravity waves (AGW) and travelling ionospheric disturbances (TID) in the Earth\\'s thermosphere and ionosphere are reviewed. In the past decade, the generation of gravity waves at high latitudes and their subsequent propagation to low latitudes have been studied by several global model simulations and coordinated observation campaigns such as the Worldwide Atmospheric Gravity-wave Study (WAGS), the results are presented in the first part of the review. The second part describes the progress towards understanding the AGW/TID characteristics. It points to the AGW/TID relationship which has been recently revealed with the aid of model-data comparisons and by the application of new inversion techniques. We describe the morphology and climatology of gravity waves and their ionospheric manifestations, TIDs, from numerous new observations.
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Dudeney, J. R., K. B. Baker, P. H. Stoker, and A. D. M. Walker. "The Southern Hemisphere Auroral Radar Experiment (SHARE)." Antarctic Science 6, no. 1 (March 1994): 123–24. http://dx.doi.org/10.1017/s0954102094000155.
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The near Earth space environment (known as Geospace) is dominated by the interaction between the solar wind and the geomagnetic field, which creates the magnetosphere. Considerable energy flows from the solar wind into the magnetosphere and ends up in the Earth's upper atmosphere (the thermosphere and ionosphere). The coupling of the geomagnetic field with that of the solar wind (known as the interplanetary magnetic field, or IMF) produces a variety of electro-dynamic responses with signatures such as electric fields and currents in the polar ionospheres. These produce, inter alia, motion of the ionospheric plasma (at altitudes between 100 and 1000kms) which can be monitored from the ground using radar techniques. Analysis of such plasma motion provides a very powerful means of investigating the nature of the interactions taking place at the boundaries between the magnetosphere and the solar wind. To do this effectively requires simultaneous measurements over as large an area (in latitude and longitude) as possible.
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Limberger, M., W. Liang, M. Schmidt, D. Dettmering, and U. Hugentobler. "Regional representation of F2 Chapman parameters based on electron density profiles." Annales Geophysicae 31, no. 12 (December 20, 2013): 2215–27. http://dx.doi.org/10.5194/angeo-31-2215-2013.
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Abstract. Understanding the physical processes within the ionosphere is a key requirement to improve and extend ionospheric modeling approaches. The determination of meaningful parameters to describe the vertical electron density distribution and how they are influenced by the solar activity is an important topic in ionospheric research. In this regard, the F2 layer of the ionosphere plays a key role as it contains the highest concentration of electrons and ions. In this contribution, the maximum electron density NmF2, peak height hmF2 and scale height HF2 of the F2 layer are determined by employing a model approach for regional applications realized by the combination of endpoint-interpolating polynomial B splines with an adapted physics-motivated Chapman layer. For this purpose, electron density profiles derived from ionospheric GPS radio occultation measurements of the satellite missions FORMOSAT-3/COSMIC, GRACE and CHAMP have been successfully exploited. Profiles contain electron density observations at discrete spots, in contrast to the commonly used integrated total electron content from GNSS, and therefore are highly sensitive to obtaining the required information of the vertical electron density structure. The spatio-temporal availability of profiles is indeed rather sparse, but the model approach meets all requirements to combine observation techniques implicating the mutual support of the measurements concerning accuracy, sensitivity and data resolution. For the model initialization and to bridge observation gaps, the International Reference Ionosphere 2007 is applied. Validations by means of simulations and selected real data scenarios show that this model approach has significant potential and the ability to yield reliable results.
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Tereshchenko, E. D., B. Z. Khudukon, M. O. Kozlova, and T. Nygrén. "Anisotropy of ionospheric irregularities determined from the amplitude of satellite signals at a single receiver." Annales Geophysicae 17, no. 4 (April 30, 1999): 508–18. http://dx.doi.org/10.1007/s00585-999-0508-4.
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Abstract. A new method of determining the anisotropy parameters of small-scale irregularities in the ionospheric F region is presented and experimental results are shown. The method is based on observations of amplitude fluctuations of radio waves transmitted by satellites flying above the F region. In practice, Russian navigational satellites are used and both the amplitude and the phase of the received signal is measured on the ground level. The method determines both the field-aligned anisotropy and the field-perpendicular anisotropy and orientation of the spatial spectrum of the irregularities, assuming that the contours of constant power have an elliptic shape. A possibility of applying the method to amplitude tomography is also discussed. Using a chain of receivers on the ground level, one could locate the regions of small-scale irregularities as well as determine their relative intensities. Then the large-scale background structures could be mapped simultaneously by means of ordinary ray tomography using the phase observations, and therefore the relations of small-scale and large-scale structures could be investigated.Key words. Ionosphere (auroral ionosphere; ionospheric irregularities; instruments and techniques)
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Chisham, G., and M. Pinnock. "Assessing the contamination of SuperDARN global convection maps by non-F-region backscatter." Annales Geophysicae 20, no. 1 (January 31, 2002): 13–28. http://dx.doi.org/10.5194/angeo-20-13-2002.
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Abstract. Global convection mapping using line-of-sight Doppler velocity data from the Super Dual Auroral Radar Network (SuperDARN) is now an accepted method of imaging high-latitude ionospheric convection. This mapping process requires that the flow measured by the radars is defined solely by the convection electric field. This is generally only true of radar backscatter from the ionospheric F-region. We investigate the extent to which the E-region and ground backscatter in the SuperDARN data set may be misidentified as F-region backscatter, and assess the contamination of global convection maps which results from the addition of this non-F-region backscatter. We present examples which highlight the importance of identifying this contamination, especially with regard to the mesoscale structure in the convection maps.Key words. Ionosphere (plasma convection) – Radio science (radio wave propagation; instruments and techniques)
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Materassi, Massimo, Tommaso Alberti, Yenca Migoya-Orué, Sandro Maria Radicella, and Giuseppe Consolini. "Chaos and Predictability in Ionospheric Time Series." Entropy 25, no. 2 (February 17, 2023): 368. http://dx.doi.org/10.3390/e25020368.
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Modelling the Earth’s ionosphere is a big challenge, due to the complexity of the system. Different first principle models have been developed over the last 50 years, based on ionospheric physics and chemistry, mostly controlled by Space Weather conditions. However, it is not understood in depth if the residual or mismodelled component of the ionosphere’s behaviour is predictable in principle as a simple dynamical system, or is conversely so chaotic to be practically stochastic. Working on an ionospheric quantity very popular in aeronomy, we here suggest data analysis techniques to deal with the question of how chaotic and how predictable the local ionosphere’s behaviour is. In particular, we calculate the correlation dimension D2 and the Kolmogorov entropy rate K2 for two one-year long time series of data of vertical total electron content (vTEC), collected on the top of the mid-latitude GNSS station of Matera (Italy), one for the year of Solar Maximum 2001 and one for the year of Solar Minimum 2008. The quantity D2 is a proxy of the degree of chaos and dynamical complexity. K2 measures the speed of destruction of the time-shifted self-mutual information of the signal, so that K2−1 is a sort of maximum time horizon for predictability. The analysis of the D2 and K2 for the vTEC time series allows to give a measure of chaos and predictability of the Earth’s ionosphere, expected to limit any claim of prediction capacity of any model. The results reported here are preliminary, and must be intended only to demonstrate how the application of the analysis of these quantities to the ionospheric variability is feasible, and with a reasonable output.
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Afraimovich, E. L., E. I. Astafieva, and S. V. Voyeikov. "Isolated ionospheric disturbances as deduced from global GPS network." Annales Geophysicae 22, no. 1 (January 1, 2004): 47–62. http://dx.doi.org/10.5194/angeo-22-47-2004.
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Abstract. We investigate an unusual class of medium-scale traveling ionospheric disturbances of the nonwave type, isolated ionospheric disturbances (IIDs) that manifest themselves in total electron content (TEC) variations in the form of single aperiodic negative TEC disturbances of a duration of about 10min (the total electron content spikes, TECS). The data were obtained using the technology of global detection of ionospheric disturbances using measurements of TEC variations from a global network of receivers of the GPS. For the first time, we present the TECS morphology for 170 days in 1998–2001. The total number of TEC series, with a duration of each series of about 2.3h (2h18m), exceeded 850000. It was found that TECS are observed in no more than 1–2% of the total number of TEC series mainly in the nighttime in the spring and autumn periods. The TECS amplitude exceeds the mean value of the "background" TEC variation amplitude by a factor of 5–10 as a minimum. TECS represent a local phenomenon with a typical radius of spatial correlation not larger than 500km. The IID-induced TEC variations are similar in their amplitude, form and duration to the TEC response to shock-acoustic waves (SAW) generated during rocket launchings and earthquakes. However, the IID propagation velocity is less than the SAW velocity (800–1000m/s) and are most likely to correspond to the velocity of background medium-scale acoustic-gravity waves, on the order of 100–200m/s. Key words. Ionosphere (ionospheric irregularities, instruments and techniques) - Radio science (ionospheric propagation)
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Yeoman, T. K., D. M. Wright, T. R. Robinson, J. A. Davies, and M. Rietveld. "High spatial and temporal resolution observations of an impulse-driven field line resonance in radar backscatter artificially generated with the Tromsø heater." Annales Geophysicae 15, no. 6 (June 30, 1997): 634–44. http://dx.doi.org/10.1007/s00585-997-0634-9.
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Abstract. The CUTLASS Finland HF radar has been operated in conjunction with the EISCAT Tromsø RF ionospheric heater facility to examine a ULF wave characteristic of the development of a field line resonance (FLR) driven by a cavity mode caused by a magnetospheric impulse. When the heater is on, striating the ionosphere with field-aligned ionospheric electron density irregularities, a large enough radar target is generated to allow post-integration over only 1 second. When combined with 15 km range gates, this gives radar measurements of a naturally occurring ULF wave at a far better temporal and spatial resolution than has been achieved previously. The time-dependent signature of the ULF wave has been examined as it evolves from a large-scale cavity resonance, through a transient where the wave period was latitude-dependent and the oscillation had the characteristics of freely ringing field lines, and finally to a very narrow, small-scale local field line resonance. The resonance width of the FLR is only 60 km and this is compared with previous observations and theory. The FLR wave signature is strongly attenuated in the ground magnetometer data. The characterisation of the impulse driven FLR was only achieved very crudely with the ground magnetometer data and, in fact, an accurate determination of the properties of the cavity and field line resonant systems challenges the currently available limitations of ionospheric radar techniques. The combination of the latest ionospheric radars and facilities such as the Tromsø ionospheric heater can result in a powerful new tool for geophysical research.
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Stolle, C., N. Jakowski, K. Schlegel, and M. Rietveld. "Comparison of high latitude electron density profiles obtained with the GPS radio occultation technique and EISCAT measurements." Annales Geophysicae 22, no. 6 (June 14, 2004): 2015–22. http://dx.doi.org/10.5194/angeo-22-2015-2004.
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Abstract. To obtain a comprehensive view on high latitude processes by applying different observation techniques, the SIRCUS campaign was initiated in 2001/2002. This paper compares electron density profiles derived from CHAMP radio occultation data and those measured with the EISCAT facility. Since ionospheric profiling with the help of space-based received GPS is a relatively new technique, validations with established independent instruments are of crucial need. We present 28 profiling events for quasi-statistical analyses, which occurred during the SIRCUS campaigns and describe some of them in more detail. We found out that the majority of profile comparisons in electron density peak value and height, as well as in TEC, lie within the error ranges of the two methods. Differences in the ionospheric quantities do not necessarily occur when the locations of the occultation and of the radar site show considerable distances. Differences are more pronounced when the ionosphere is remarkably structured.
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Cherniak, Iurii, Irina Zakharenkova, John Braun, Qian Wu, Nicholas Pedatella, William Schreiner, Jan-Peter Weiss, and Douglas Hunt. "Accuracy assessment of the quiet-time ionospheric F2 peak parameters as derived from COSMIC-2 multi-GNSS radio occultation measurements." Journal of Space Weather and Space Climate 11 (2021): 18. http://dx.doi.org/10.1051/swsc/2020080.
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The Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) mission was launched into a low-inclination (24°) orbit on June 25, 2019. Six satellites, each with an advanced Tri-GNSS Radio-Occultation Receiver System (TGRS), provide a global and uniform data coverage of the equatorial region with several thousand electron density profiles daily. The COSMIC-2 electron density profiles, and specifically the derived ionospheric F2 peak parameters, are properly validated in this study with reliable “truth” observations. For this purpose, we used manually scaled ionograms from 29 ground-based ionosondes located globally at low and middle latitudes. For this validation campaign, we considered only geomagnetically quiet conditions in order to establish benchmark level of the new mission’s ionospheric observation quality and to evaluate the operational capability of the COSMIC-2 Radio Occultation (RO) payload at the background of normal day-to-day variability of the ionosphere. For reliable colocations between two independent techniques, we selected only COSMIC-2 RO profiles whose F2 peak point coordinates were within 5° of the closest ionosonde. Our comparison of the ionospheric F2 peak height (hmF2) derived from COSMIC-2 RO and ground-based ionosonde measurements showed a very good agreement, with a mean of ~5 and ~2 km at low and middle latitudes, respectively, while RMS error was of ~23 and ~14 km, respectively. That range corresponds to a deviation of only 6–9% from the reference, ionosonde observations. Examination of representative collocation events with multiple (2–5) simultaneous RO tracks near the same ionosonde with different RO geometry, multi-satellite and multi-GNSS combination give us observational evidence that COSMIC-2 RO-based EDPs derived from GPS and GLONAS links show good self-consistency in terms of the ionospheric F2 peak values and electron density profile shape. We can conclude that COSMIC-2 provides high quality data for specification the ionospheric electron density at the F2 peak region.
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Leonovich, L. A., E. L. Afraimovich, E. B. Romanova, and A. V. Taschilin. "Estimating the contribution from different ionospheric regions to the TEC response to the solar flares using data from the international GPS network." Annales Geophysicae 20, no. 12 (December 31, 2002): 1935–41. http://dx.doi.org/10.5194/angeo-20-1935-2002.
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Abstract. This paper proposes a new method for estimating the contribution from different ionospheric regions to the response of total electron content variations to the solar flare, based on data from the international network of two-frequency multichannel receivers of the navigation GPS system. The method uses the effect of partial "shadowing" of the atmosphere by the terrestrial globe. The study of the solar flare influence on the atmosphere uses GPS stations located near the boundary of the shadow on the ground in the nightside hemisphere. The beams between the satellite-borne transmitter and the receiver on the ground for these stations pass partially through the atmosphere lying in the region of total shadow, and partially through the illuminated atmosphere. The analysis of the ionospheric effect of a powerful solar flare of class X5.7/3B that was recorded on 14 July 2000 (10:24 UT, N22 W07) in quiet geomagnetic conditions (Dst = -10 nT) has shown that about 75% of the TEC increase corresponds to the ionospheric region lying below 300 km and about 25% to regions lying above 300 km.Key words. Ionosphere (solar radiation and cosmic ray effects; instruments and techniques) – Solar physics, astrophysics and astronomy (ultraviolet emissions)
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Aruliah, A. L., and E. Griffin. "Evidence of meso-scale structure in the high-latitude thermosphere." Annales Geophysicae 19, no. 1 (January 31, 2001): 37–46. http://dx.doi.org/10.5194/angeo-19-37-2001.
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Abstract. There is a widely held assumption that the thermospheric neutral gas is slow to respond to magnetospheric forcing owing to its large inertia and therefore, may be treated as a steady state background medium for the more dynamic ionosphere. This is shown to be over simplistic. The data presented here compare direct measurements of the thermospheric neutral winds made in Northern Scandinavia by Fabry-Perot Interferometers (FPIs) with direct measurements of the ionosphere made by the EISCAT radar and with model simulations. These comparisons will show that the neutral atmosphere is capable of responding to ionospheric changes on mesoscale levels, i.e., spatial and temporal scale sizes of less than a few hundred kilometres and tens of minutes, respectively.Key words. Atmospheric composition and structure (air-glow and aurora; instruments and techniques) – Ionosphere (ionosphere-atmosphere interactions)
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Turunen, T., J. Markkanen, and A. P. van Eyken. "Ground clutter cancellation in incoherent radars: solutions for EISCAT Svalbard radar." Annales Geophysicae 18, no. 9 (September 30, 2000): 1242–47. http://dx.doi.org/10.1007/s00585-000-1242-0.
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Abstract. Incoherent scatter radars measure ionosphere parameters using modified Thomson scatter from free electrons in the target (see e.g. Hagfors, 1997). The integrated cross section of the ionospheric scatterers is extremely small and the measurements can easily be disturbed by signals returned by unwanted targets. Ground clutter signals, entering via the antenna side lobes, can render measurements at the nearest target ranges totally impossible. The EISCAT Svalbard Radar (ESR), which started measurements in 1996, suffers from severe ground clutter and the ionosphere cannot be measured in any simple manner at ranges less than about 120–150 km, depending on the modulation employed. If the target and clutter signals have different, and clearly identifiable, properties then, in principle, there are always ways to eliminate the clutter. In incoherent scatter measurements, differences in the coherence times of the wanted and unwanted signals can be used for clutter cancellation. The clutter cancellation must be applied to all modulations, usually alternating codes in modern experiments, used for shorter ranges. Excellent results have been obtained at the ESR using a simple pulse-to-pulse clutter subtraction method, but there are also other possibilities.Key words: Radio science (ionospheric physics; signal processing; instruments and techniques)
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El-Rahman, Mahmoud Abd, and Ahmed El-Rabbany. "Performance Evaluation of USTEC Product for Single-Frequency Precise Point Positioning." GEOMATICA 67, no. 4 (December 2013): 253–57. http://dx.doi.org/10.5623/cig2013-051.
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Geodetic-grade dual-frequency GPS receivers are typically used for precise point positioning (PPP). Unfortunately, these receiver systems are expensive and may not provide a cost-effective solution in many instances. The use of low-cost single-frequency GPS receivers, on the other hand, are limited by the effect of ionospheric delay. A number of mitigation techniques have been proposed to account for the effect of ionospheric delay for single-frequency GPS users. Unfortunately, however, those mitigation techniques are not suitable for PPP. More recently, the U.S. Total Electron Content (USTEC) product has been developed by the National Oceanic and Atmospheric Administration (NOAA), which describes the ionospheric total electron content in high resolution over most of North America. This paper investigates the performance of USTEC and studies its effect on single-frequency PPP solution. A performance comparison with two widely-used ionospheric mitigation models is also presented.
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Dyrud, Lars, Aleksandar Jovancevic, Andrew Brown, Derek Wilson, and Suman Ganguly. "Ionospheric measurement with GPS: Receiver techniques and methods." Radio Science 43, no. 6 (November 8, 2008): n/a. http://dx.doi.org/10.1029/2007rs003770.
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Aksnes, A., O. Amm, J. Stadsnes, N. Østgaard, G. A. Germany, R. R. Vondrak, and I. Sillanpää. "Ionospheric conductances derived from satellite measurements of auroral UV and X-ray emissions, and ground-based electromagnetic data: a comparison." Annales Geophysicae 23, no. 2 (February 28, 2005): 343–58. http://dx.doi.org/10.5194/angeo-23-343-2005.
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Abstract. Global instantaneous conductance maps can be derived from remote sensing of UV and X-ray emissions by the UVI and PIXIE cameras on board the Polar satellite. Another technique called the 1-D method of characteristics provides mesoscale instantaneous conductance profiles from the MIRACLE ground-based network in Northern Scandinavia, using electric field measurements from the STARE coherent scatter radar and ground magnetometer data from the IMAGE network. The method based on UVI and PIXIE data gives conductance maps with a resolution of ~800km in space and ~4.5min in time, while the 1-D method of characteristics establishes conductances every 20s and with a spatial resolution of ~50km. In this study, we examine three periods with substorm activity in 1998 to investigate whether the two techniques converge when the results from the 1-D method of characteristics are averaged over the spatial and temporal resolution of the UVI/PIXIE data. In general, we find that the calculated conductance sets do not correlate. However, a fairly good agreement may be reached when the ionosphere is in a state that does not exhibit strong local turbulence. By defining a certain tolerance level of turbulence, we show that 14 of the 15 calculated conductance pairs during relatively uniform ionospheric conditions differ less than ±30%. The same is true for only 4 of the 9 data points derived when the ionosphere is in a highly turbulent state. A correlation coefficient between the two conductance sets of 0.27 is derived when all the measurements are included. By removing the data points from time periods when too much ionospheric turbulence occurs, the correlation coefficient raises to 0.57. Considering the two very different techniques used in this study to derive the conductances, with different assumptions, limitations and scale sizes, our results indicate that simple averaging of mesoscale results allows a continuous transition to large-scale results. Therefore, it is possible to use a combined approach to study ionospheric events with satellite optical and ground-based electrodynamic data of different spatial and temporal resolutions. We must be careful, though, when using these two techniques during disturbed conditions. The two methods will only give results that systematically converge when relatively uniform conditions exist.
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Gerzen, T., and D. Minkwitz. "Simultaneous multiplicative column-normalized method (SMART) for 3-D ionosphere tomography in comparison to other algebraic methods." Annales Geophysicae 34, no. 1 (January 22, 2016): 97–115. http://dx.doi.org/10.5194/angeo-34-97-2016.
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Abstract. The accuracy and availability of satellite-based applications like GNSS positioning and remote sensing crucially depends on the knowledge of the ionospheric electron density distribution. The tomography of the ionosphere is one of the major tools to provide link specific ionospheric corrections as well as to study and monitor physical processes in the ionosphere. In this paper, we introduce a simultaneous multiplicative column-normalized method (SMART) for electron density reconstruction. Further, SMART+ is developed by combining SMART with a successive correction method. In this way, a balancing between the measurements of intersected and not intersected voxels is realised. The methods are compared with the well-known algebraic reconstruction techniques ART and SART. All the four methods are applied to reconstruct the 3-D electron density distribution by ingestion of ground-based GNSS TEC data into the NeQuick model. The comparative case study is implemented over Europe during two periods of the year 2011 covering quiet to disturbed ionospheric conditions. In particular, the performance of the methods is compared in terms of the convergence behaviour and the capability to reproduce sTEC and electron density profiles. For this purpose, independent sTEC data of four IGS stations and electron density profiles of four ionosonde stations are taken as reference. The results indicate that SMART significantly reduces the number of iterations necessary to achieve a predefined accuracy level. Further, SMART+ decreases the median of the absolute sTEC error up to 15, 22, 46 and 67 % compared to SMART, SART, ART and NeQuick respectively.
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Aksenov, Oleg, Stanislav Kozlov, Andrey Lyakhov, Vyacheslav Trekin, Yuriy Perunov, and Sergey Yakubovsky. "ANALYZING EXISTING APPLIED MODELS OF THE IONOSPHERE FOR CALCULATING RADIO WAVE PROPAGATION AND POSSIBILITY OF THEIR USE FOR RADAR SYSTEMS. I. CLASSIFICATION OF APPLIED MODELS AND THE MAIN REQUIREMENTS IMPOSED ON THEM FOR RADAR AIDS." Solar-Terrestrial Physics 6, no. 1 (April 1, 2020): 69–76. http://dx.doi.org/10.12737/stp-61202008.
Full textAbstract:
We review modern HF–X band radars covering over-the-horizon problems. The ionosphere significantly affects wave propagation in all the bands. We describe available correction techniques, which use additional evidence on the ionosphere, as well as models of different degrees of complexity. The fact that the field of view cannot be covered by ground-based instruments as well as the growing requirements to the precision and stability of the radars result in the impossibility of ionospheric correction with up-to-date models, hence the latter require further elaboration. We give a virtually full classification of the models. The article summarizes the requirements to the models for the radars depending on their function.
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Aksenov, Oleg, Stanislav Kozlov, Andrey Lyakhov, Vyacheslav Trekin, Yuriy Perunov, and Sergey Yakubovsky. "ANALYZING EXISTING APPLIED MODELS OF THE IONOSPHERE FOR CALCULATING RADIO WAVE PROPAGATION AND POSSIBILITY OF THEIR USE FOR RADAR SYSTEMS. I. CLASSIFICATION OF APPLIED MODELS AND THE MAIN REQUIREMENTS IMPOSED ON THEM FOR RADAR AIDS." Solnechno-Zemnaya Fizika 6, no. 1 (March 30, 2020): 86–96. http://dx.doi.org/10.12737/szf-61202008.
Full textAbstract:
We review modern HF–X band radars covering over-the-horizon problems. The ionosphere significantly affects wave propagation in all the bands. We describe available correction techniques, which use additional evidence on the ionosphere, as well as models of different degrees of complexity. The fact that the field of view cannot be covered by ground-based instruments as well as the growing requirements to the precision and stability of the radars result in the impossibility of ionospheric correction with up-to-date models, hence the latter require further elaboration. We give a virtually full classification of the models. The article summarizes the requirements to the models for the radars depending on their function.
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Nielsen, E., F. Honary, and M. Grill. "Time resolution of cosmic noise observations with acorrelation experiment." Annales Geophysicae 22, no. 5 (April 8, 2004): 1687–89. http://dx.doi.org/10.5194/angeo-22-1687-2004.
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Abstract. A radio wave correlation experiment using a Mills Cross technique can be used to observe the cosmic noise intensity from the ground for the purpose of determining the absorption in the ionosphere. To ensure a time resolution of 10 to 20s of the absorption observations, it is necessary that the autocorrelation function of the signal received within a wanted spatial resolution and in a given receiver is >8% of the total signal amplitude incident on that receiver.Key words. Radio Science (Instruments and techniques; Interferometry; Ionospheric physics)
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Dabas, R. S., and L. Kersley. "Study of mid-latitude nighttime enhancement in F-region electron density using tomographic images over the UK." Annales Geophysicae 21, no. 12 (December 31, 2003): 2323–28. http://dx.doi.org/10.5194/angeo-21-2323-2003.
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Abstract. Nighttime enhancements in ionospheric electron content (IEC)/peak electron density (NmF2) have been studied by various workers in the equatorial anomaly and mid-latitude regions. Such studies give an idea about their enhancement over that location only. In the present study tomographic images over the UK, which give a latitudinal versus height distributions of ionospheric electron density in a much wider area, have been used to study the anomalous increases in nighttime F-region electron density at mid-latitudes. From the analysis of four seasonal representative months (November 1997, March, June and October 1998) data it was noted that the majority of the cases of nighttime enhancements were observed after local midnight, with a maximum between 03:00–04:00 LT in the month of November 1997. Enhancements were observed mostly between 45–50° N latitudes, and their positions are not affected by magnetic activity (Kp ) variations, whereas the separation between the mid-latitude trough and enhancement decreases with increases in magnetic activity. This finding shows that only the trough moves equatorward with the increase in magnetic activity. It is also noted that the electron density gradient from the trough to the enhancement increases with an increase in Kp. Results are discussed in terms of downward plasma transport from the protonosphere to the ionosphere and the nighttime neutral winds.Key words. Ionosphere (mid-latitude ionosphere; modeling and forecasting; instruments and techniques)
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Denisenko, P. F., N. V. Nastasyina, and V. I. Vodolazkin. "Usage of regularization techniques for effective electron collision frequency determination from oblique ionospheric sounding." Annales Geophysicae 14, no. 8 (August 31, 1996): 811–15. http://dx.doi.org/10.1007/s00585-996-0811-2.
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Abstract. Computer modelling is used to investigate the possibility of determining ionospheric parameters from slightly oblique ionospheric soundings, using absorption data for decametric radio waves of different polarization. It is shown that with mean square measurement errors of 0.5 dB, and using regularization algorithms to solve the inverse problems, electron collision frequency profiles can be obtained for the night F-region with errors of less than 30%. Both temperatures of electrons and neutrals are also determined to within 10%.