Remote Sensing

Editorial

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8 pages, 250 KiB

Open AccessEditorial

Ionosphere Monitoring with Remote Sensing

by Fabio Giannattasio

Remote Sens. 2022, 14(21), 5325; https://doi.org/10.3390/rs14215325 - 25 Oct 2022

Cited by 3 | Viewed by 1625

Abstract

Characterising the physical properties of the Earth’s ionosphere is fundamental to shed light on the dynamic processes occurring therein on a wide range of both spatial and temporal scales and to understand several phenomena relevant to Space Weather [...] Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

Research

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15 pages, 1742 KiB

Open AccessArticle

Advanced Classification of Ionospheric Troughs in the Morning and Evening Conditions

by Alexander Karpachev

Remote Sens. 2022, 14(16), 4072; https://doi.org/10.3390/rs14164072 - 20 Aug 2022

Cited by 7 | Viewed by 1378

Abstract

The separation and classification of ionospheric troughs in the winter evening and morning ionospheres of the southern hemisphere were performed using CHAMP satellite data for high solar activity (2000–2002). In the high-latitude ionosphere, the main ionospheric trough (MIT) was separated from the high-latitude [...] Read more.

The separation and classification of ionospheric troughs in the winter evening and morning ionospheres of the southern hemisphere were performed using CHAMP satellite data for high solar activity (2000–2002). In the high-latitude ionosphere, the main ionospheric trough (MIT) was separated from the high-latitude trough (HLT). The separation was carried out using a thorough analysis of all the characteristic structures of the ionosphere in the framework of the auroral diffuse particle precipitation model. Two types of high-latitude troughs were identified: (1) a wide trough associated with zone II of diffuse precipitation on the poleward edge of the auroral oval and (2) a narrow trough of ionization, which is presumably associated with an electric field action. The poleward wall of MIT is as ever formed by diffuse precipitation in zone I on the equatorward edge of the auroral oval. The HLT and MIT separation is most difficult at the longitudes of the eastern hemisphere, where all structures are located at the highest latitudes and partially overlap. In the mid-latitude ionosphere, all the characteristic structures of the ionosphere were also identified and considered. MIT was separated from the ring ionospheric trough (RIT), which is formed by the decay processes of the magnetospheric ring current. The separation of MIT and RIT was performed based on an analysis of the prehistory of all geomagnetic disturbances during the period under study. In addition to the RIT, a decrease in the electron density equatorward of the MIT was found to be often formed at the America–Atlantic longitudes, which masks the MIT minimum. For completeness, all cases of a clearly defined polar cavity are also presented. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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25 pages, 14523 KiB

Open AccessArticle

Ionospheric Behavior during the 10 June 2021 Annular Solar Eclipse and Its Impact on GNSS Precise Point Positioning

by Juan Carlos Valdés-Abreu, Marcos A. Díaz, Manuel Bravo, Juan Carlos Báez and Yohadne Stable-Sánchez

Remote Sens. 2022, 14(13), 3119; https://doi.org/10.3390/rs14133119 - 29 Jun 2022

Cited by 8 | Viewed by 2697

Abstract

The main effects of the 10 June 2021 annular solar eclipse on GNSS position estimation accuracy are presented. The analysis is based on TEC measurements made by 2337 GNSS stations around the world. TEC perturbations were obtained by comparing results 2 days prior [...] Read more.

The main effects of the 10 June 2021 annular solar eclipse on GNSS position estimation accuracy are presented. The analysis is based on TEC measurements made by 2337 GNSS stations around the world. TEC perturbations were obtained by comparing results 2 days prior to and after the day of the event. For the analysis, global TEC maps were created using ordinary Kriging interpolation. From TEC changes, the apparent position variation was obtained using the post-processing kinematic precise point positioning with ambiguity resolution (PPP-AR) mode. We validated the TEC measurements by contrasting them with data from the Swarm-A satellite and four digiosondes in Central/South America. The TEC maps show a noticeable TEC depletion (<−60%) under the moon’s shadow. Important variations of TEC were also observed in both crests of the Equatorial Ionization Anomaly (EIA) region over the Caribbean and South America. The effects on GNSS precision were perceived not only close to the area of the eclipse but also as far as the west coast of South America (Chile) and North America (California). The number of stations with positioning errors of over 10 cm almost doubled during the event in these regions. The effects were sustained longer (∼10 h) than usually assumed. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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14 pages, 3811 KiB

Open AccessArticle

Assessment of Polar Ionospheric Observations by VIPIR/Dynasonde at Jang Bogo Station, Antarctica: Part 1—Ionospheric Densities

by Eunsol Kim, Geonhwa Jee, Young-Bae Ham, Nikolay Zabotin, Changsup Lee, Hyuck-Jin Kwon, Junseok Hong, Jeong-Han Kim and Terence Bullett

Remote Sens. 2022, 14(12), 2785; https://doi.org/10.3390/rs14122785 - 10 Jun 2022

Cited by 6 | Viewed by 1978

Abstract

Vertical incidence pulsed ionospheric radar (VIPIR) has been operated to observe the polar ionosphere with Dynasonde analysis software at Jang Bogo Station (JBS), Antarctica, since 2017. The JBS-VIPIR-Dynasonde (JVD) provides ionospheric parameters such as the height profile of electron density with NmF2 and [...] Read more.

Vertical incidence pulsed ionospheric radar (VIPIR) has been operated to observe the polar ionosphere with Dynasonde analysis software at Jang Bogo Station (JBS), Antarctica, since 2017. The JBS-VIPIR-Dynasonde (JVD) provides ionospheric parameters such as the height profile of electron density with NmF2 and hmF2, the ion drift, and the ionospheric tilt in the bottomside ionosphere. The JBS (74.6°S, 164.2°E) is located in the polar cap, cusp, or auroral region depending on the geomagnetic activity and local time. In the present study, an initial assessment of JVD ionospheric densities is attempted by the comparison with GPS TEC measurements which are simultaneously obtained from the GPS receiver at JBS during the solar minimum period from 2017 to 2019. It is found that the JVD NmF2 and bottomside TEC (bTEC) show a generally good correlation with GPS TEC for geomagnetically quiet conditions. However, the bTEC seems to be less correlated with the GPS TEC with slightly larger spreads especially during the daytime and in summer, which seems to be associated with the characteristics of the polar ionosphere such as energetic particle precipitations and large density irregularities. It is also found that the Dynasonde analysis seems to show some limitations to handle these characteristics of the polar ionosphere and needs to be improved to produce more accurate ionospheric density profiles especially during disturbed conditions. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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22 pages, 5262 KiB

Open AccessArticle

A Preliminary Study on Ionospheric Scintillation Anomalies Detected Using GNSS-R Data from NASA CYGNSS Mission as Possible Earthquake Precursors

by Carlos Molina, Badr-Eddine Boudriki Semlali, Hyuk Park and Adriano Camps

Remote Sens. 2022, 14(11), 2555; https://doi.org/10.3390/rs14112555 - 26 May 2022

Cited by 10 | Viewed by 2355

Abstract

Ionospheric perturbations affect the propagation of electromagnetic waves. These perturbations, besides being a problem for space communications, satellite navigation, and Earth observation techniques, could also be used as another Earth observation tool. Several recent studies showed correlations with earthquakes with ionospheric anomalies, but [...] Read more.

Ionospheric perturbations affect the propagation of electromagnetic waves. These perturbations, besides being a problem for space communications, satellite navigation, and Earth observation techniques, could also be used as another Earth observation tool. Several recent studies showed correlations with earthquakes with ionospheric anomalies, but almost all of them use ground stations to measure the Total Electron Content (TEC) variations, and, in particular, the ones occurring after an earthquake. Here, a preliminary study is presented on how the ionospheric scintillation measured with GNSS-R instruments over oceanic regions shows a small, but detectable correlation with the occurrence of earthquakes, which in some cases occurs before the earthquakes. This study uses GNSS-R data from NASA CYGNSS Mission to measure the ionospheric amplitude scintillation (

S_{4}

) for 6 months from March 2019 to August 2019, applying a statistical analysis based on confusion matrixes, and the Receiver Operating Characteristic (ROC) curves to correlate

S_{4}

anomalous variations to earthquakes. A small positive correlation is found between the ionospheric scintillation and the earthquakes during the six previous days. However, the study has some weakness because (a) a small number (∼45) of large (M > 6) earthquakes over oceanic regions are studied, (b) the region studied is close to the geomagnetic equator, where ionospheric scintillations are usual, and (c) the overall correlation is small. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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20 pages, 1517 KiB

Open AccessArticle

On Turbulent Features of E × B Plasma Motion in the Auroral Topside Ionosphere: Some Results from CSES-01 Satellite

by Giuseppe Consolini, Virgilio Quattrociocchi, Simone Benella, Paola De Michelis, Tommaso Alberti, Mirko Piersanti and Maria Federica Marcucci

Remote Sens. 2022, 14(8), 1936; https://doi.org/10.3390/rs14081936 - 17 Apr 2022

Cited by 3 | Viewed by 1897

Abstract

The recent Chinese Seismo-Electromagnetic Satellite (CSES-01) provides a good opportunity to investigate some features of plasma properties and its motion in the topside ionosphere. Using simultaneous measurements from the electric field detector and the magnetometers onboard CSES-01, we investigate some properties of the [...] Read more.

The recent Chinese Seismo-Electromagnetic Satellite (CSES-01) provides a good opportunity to investigate some features of plasma properties and its motion in the topside ionosphere. Using simultaneous measurements from the electric field detector and the magnetometers onboard CSES-01, we investigate some properties of the plasma E × B drift velocity for a case study during a crossing of the Southern auroral region in the topside ionosphere. In detail, we analyze the spectral and scaling features of the plasma drift velocity and provide evidence of the turbulent character of the E × B drift. Our results provide an evidence of the occurrence of 2D E × B intermittent convective turbulence for the plasma motion in the topside ionospheric F2 auroral region at scales from tens of meters to tens of kilometers. The intermittent character of the observed turbulence suggests that the macro-scale intermittent structure is isomorphic with a quasi-1D fractal structure, as happens, for example, in the case of a filamentary or thin-tube-like structure. Furthermore, in the analyzed range of scales we found that both magnetohydrodynamic and kinetic processes may affect the plasma dynamics at spatial scales below 2 km. The results are discussed and compared with previous results reported in the literature. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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18 pages, 12034 KiB

Open AccessArticle

Pressure-Gradient Current at High Latitude from Swarm Measurements

by Giulia Lovati, Paola De Michelis, Giuseppe Consolini and Francesco Berrilli

Remote Sens. 2022, 14(6), 1428; https://doi.org/10.3390/rs14061428 - 15 Mar 2022

Cited by 3 | Viewed by 2371

Abstract

The pressure-gradient current is among the weaker ionospheric current systems arising from plasma pressure variations. It is also called diamagnetic current because it produces a magnetic field which is oriented oppositely to the ambient magnetic field, causing its reduction. The magnetic reduction can [...] Read more.

The pressure-gradient current is among the weaker ionospheric current systems arising from plasma pressure variations. It is also called diamagnetic current because it produces a magnetic field which is oriented oppositely to the ambient magnetic field, causing its reduction. The magnetic reduction can be revealed in measurements made by low-Earth orbiting satellites flying close to ionospheric plasma regions where rapid changes in density occur. Using geomagnetic field, plasma density and electron temperature measurements recorded on board ESA Swarm A satellite from April 2014 to March 2018, we reconstruct the flow patterns of the pressure-gradient current at high-latitude ionosphere in both hemispheres, and investigate their dependence on magnetic local time, geomagnetic activity, season and solar forcing drivers. Although being small in amplitude these currents appear to be a ubiquitous phenomenon at ionospheric high latitudes characterized by well defined flow patterns, which can cause artifacts in the main field models. Our findings can be used to correct magnetic field measurements for diamagnetic current effect, to improve modern magnetic field models, as well as to understand the impact of ionospheric irregularities on ionospheric dynamics at small-scale sizes of a few tens of kilometers. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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18 pages, 5392 KiB

Open AccessArticle

Magnetic Field and Electron Density Scaling Properties in the Equatorial Plasma Bubbles

by Paola De Michelis, Giuseppe Consolini, Tommaso Alberti, Roberta Tozzi, Fabio Giannattasio, Igino Coco, Michael Pezzopane and Alessio Pignalberi

Remote Sens. 2022, 14(4), 918; https://doi.org/10.3390/rs14040918 - 14 Feb 2022

Cited by 5 | Viewed by 2077

Abstract

The ionospheric plasma density irregularities are known to play a role in the propagation of electromagnetic signals and to be one of the most important sources of disturbance for the Global Navigation Satellite System, being responsible for degradation and, sometimes, interruptions of the [...] Read more.

The ionospheric plasma density irregularities are known to play a role in the propagation of electromagnetic signals and to be one of the most important sources of disturbance for the Global Navigation Satellite System, being responsible for degradation and, sometimes, interruptions of the signals received by the system. In the equatorial ionospheric F region, these plasma density irregularities, known as plasma bubbles, find the suitable conditions for their development during post-sunset hours. In recent years, important features of plasma bubbles such as their dependence on latitude, longitude, and solar and geomagnetic activities have been inferred indirectly using their magnetic signatures. Here, we study the scaling properties of both the electron density and the magnetic field inside the plasma bubbles using measurements on board the Swarm A satellite from 1 April 2014 to 31 January 2016. We show that the spectral features of plasma irregularities cannot be directly inferred from their magnetic signatures. A relation more complex than the linear one is necessary to properly describe the role played by the evolution of plasma bubbles with local time and by the development of turbulent phenomena. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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18 pages, 34990 KiB

Open AccessArticle

Measurement of Aspect Angle of Field-Aligned Plasma Irregularities in Mid-Latitude E Region Using VHF Atmospheric Radar Imaging and Interferometry Techniques

by Jenn-Shyong Chen, Chien-Ya Wang and Yen-Hsyang Chu

Remote Sens. 2022, 14(3), 611; https://doi.org/10.3390/rs14030611 - 27 Jan 2022

Cited by 5 | Viewed by 2432

Abstract

Multireceiver and multifrequency radar imaging were carried out with the 46.5 MHz MU radar in Japan (34.85°N and 136.10°E) to examine the aspect sensitivity of field-aligned plasma irregularities (FAIs) in the mid-latitude ionosphere E region. A radar beam was directed to geographic north [...] Read more.

Multireceiver and multifrequency radar imaging were carried out with the 46.5 MHz MU radar in Japan (34.85°N and 136.10°E) to examine the aspect sensitivity of field-aligned plasma irregularities (FAIs) in the mid-latitude ionosphere E region. A radar beam was directed to geographic north and at 51° zenith angle, which was normal to the geomagnetic field line around 100 km height. Nineteen receivers and five carrier frequencies were used for radar imaging to retrieve the power distribution in the radar volume, and then the aspect angle along the geomagnetic field line was calculated according to the angular power distribution. Retrieval algorithms such as Fourier, Capon, and norm-constrained Capon (NC-Capon) were employed, in which the NC-Capon was applied to FAIs for the first time and found to be more suitable for the present study. The aspect angles estimated by the NC-Capon ranged between 0.1° and 0.4° mostly, and averaged around 0.2°, which were the same order to the previous measurements with radar interferometry (RI), made for equatorial electrojet irregularities and the lower mid-latitude sporadic E region. For comparison, RI-estimated aspect angles were also investigated and found to be close to that of NC-Capon, but distributed over a wider extent of angles. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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19 pages, 5547 KiB

Open AccessArticle

Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location

by Yuqiang Zhang, Zhensen Wu, Jian Feng, Tong Xu, Zhongxin Deng, Ming Ou, Wen Xiong and Weimin Zhen

Remote Sens. 2021, 13(24), 5175; https://doi.org/10.3390/rs13245175 - 20 Dec 2021

Cited by 5 | Viewed by 2832

Abstract

The ionospheric equivalent slab thickness (τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. In this paper, a comprehensive statistical analysis [...] Read more.

The ionospheric equivalent slab thickness (τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. In this paper, a comprehensive statistical analysis of the diurnal, seasonal, solar, and magnetic activity variations in the τ at Guam (144.86°E, 13.62°N, 5.54°N dip lat), which is located near the magnetic equator, is presented using the GPS-TEC and ionosonde NmF2 data during the years 2012–2017. It is found that, for geomagnetically quiet days, the τ reaches its maximum value in the noontime, and the peak value in winter and at the equinox are larger than that in summer. Moreover, there is a post-sunset peak observed in the winter and equinox, and the τ during the post-midnight period is smallest in equinox. The mainly diurnal and seasonal variation of τ can be explained within the framework of relative variation of TEC and NmF2 during different seasonal local time. The dependence of τ on the solar activity shows positive correlation during the daytime, and the opposite situation applies for the nighttime. Specifically, the disturbance index (DI), which can visually assess the relationship between instantaneous τ values and the median, is introduced in the paper to quantitatively describe the overall pattern of the geomagnetic storm effect on the τ variation. The results show that the geomagnetic storm seems to have positive effect on the τ during most of the storm-time period at Guam. An example, on the 1 June 2013, is also presented to analyze the physical mechanism. During the positive storms, the penetration electric field, along with storm time equator-ward neutral wind, tends to increase upward drift and uplift F region, causing the large increase in TEC, accompanied by a relatively small increase in NmF2. On the other hand, an enhanced equatorward wind tends to push more plasma, at low latitudes, into the topside ionosphere in the equatorial region, resulting in the TEC not undergoing severe depletion, as with NmF2, during the negative storms. The results would complement the analysis of τ behavior during quiet and disturbed conditions at equatorial latitudes in East Asia. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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28 pages, 12194 KiB

Open AccessArticle

SafeNet: SwArm for Earthquake Perturbations Identification Using Deep Learning Networks

by Pan Xiong, Dedalo Marchetti, Angelo De Santis, Xuemin Zhang and Xuhui Shen

Remote Sens. 2021, 13(24), 5033; https://doi.org/10.3390/rs13245033 - 10 Dec 2021

Cited by 15 | Viewed by 3857

Abstract

Low Earth orbit satellites collect and study information on changes in the ionosphere, which contributes to the identification of earthquake precursors. Swarm, the European Space Agency three-satellite mission, has been launched to monitor the Earth geomagnetic field, and has successfully shown that in [...] Read more.

Low Earth orbit satellites collect and study information on changes in the ionosphere, which contributes to the identification of earthquake precursors. Swarm, the European Space Agency three-satellite mission, has been launched to monitor the Earth geomagnetic field, and has successfully shown that in some cases it is able to observe many several ionospheric perturbations that occurred as a result of large earthquake activity. This paper proposes the SafeNet deep learning framework for detecting pre-earthquake ionospheric perturbations. We trained the proposed model using 9017 recent (2014–2020) independent earthquakes of magnitude 4.8 or greater, as well as the corresponding 7-year plasma and magnetic field data from the Swarm A satellite, and excellent performance has been achieved. In addition, the influence of different model inputs and spatial window sizes, earthquake magnitudes, and daytime or nighttime was explored. The results showed that for electromagnetic pre-earthquake data collected within a circular region of the epicenter and with a Dobrovolsky-defined radius and input window size of 70 consecutive data points, nighttime data provided the highest performance in discriminating pre-earthquake perturbations, yielding an F1 score of 0.846 and a Matthews correlation coefficient of 0.717. Moreover, SafeNet performed well in identifying pre-seismic ionospheric anomalies with increasing earthquake magnitude and unbalanced datasets. Hypotheses on the physical causes of earthquake-induced ionospheric perturbations are also provided. Our results suggest that the performance of pre-earthquake ionospheric perturbation identification can be significantly improved by utilizing SafeNet, which is capable of detecting precursor effects within electromagnetic satellite data. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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22 pages, 6733 KiB

Open AccessArticle

An Ionospheric Anomaly Monitor Based on the One Class Support Vector Algorithm for the Ground-Based Augmentation System

by Zhen Gao, Kun Fang, Yanbo Zhu, Zhipeng Wang and Kai Guo

Remote Sens. 2021, 13(21), 4327; https://doi.org/10.3390/rs13214327 - 28 Oct 2021

Cited by 5 | Viewed by 2428

Abstract

An ionospheric anomaly is the irregular change of the ionosphere. It may result in potential threats for the ground-based augmentation system (GBAS) supporting the high-level precision approach. To counter the hazardous anomalies caused by the steep gradient in ionospheric delays, customized monitors are [...] Read more.

An ionospheric anomaly is the irregular change of the ionosphere. It may result in potential threats for the ground-based augmentation system (GBAS) supporting the high-level precision approach. To counter the hazardous anomalies caused by the steep gradient in ionospheric delays, customized monitors are equipped in GBAS architectures. A major challenge is to rapidly detect the ionospheric gradient anomaly from environmental noise to meet the safety-critical requirements. A one-class support vector machine (OCSVM)-based monitor is developed to clearly detect ionospheric anomalies and to improve the robust detection speed. An offline-online framework based on the OCSVM is proposed to extract useful information related to anomalous characteristics in the presence of noise. To validate the effectiveness of the proposed framework, the influence of noise is fully considered and analyzed based on synthetic, semi-simulated, and real data from a typical ionospheric anomaly event. Synthetic results show that the OCSVM-based monitor can identify the anomaly that cannot be detected by other commonly-used monitors, such as the CCD-1OF, CCD-2OF and KLD-1OF. Semi-simulation results show that compared with other monitors, the newly proposed monitor can improve the average detection speed by more than 40% and decrease the minimum detectable gradient change rate to 0.002 m/s. Furthermore, in the real ionospheric anomaly event experiment, compared with other monitors, the OCSVM-based monitor can improve the detection speed by 16%. The result indicates that the proposed monitor has encouraging potential to ensure integrity of the GBAS. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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25 pages, 36231 KiB

Open AccessArticle

On the Electron Temperature in the Topside Ionosphere as Seen by Swarm Satellites, Incoherent Scatter Radars, and the International Reference Ionosphere Model

by Alessio Pignalberi, Fabio Giannattasio, Vladimir Truhlik, Igino Coco, Michael Pezzopane, Giuseppe Consolini, Paola De Michelis and Roberta Tozzi

Remote Sens. 2021, 13(20), 4077; https://doi.org/10.3390/rs13204077 - 12 Oct 2021

Cited by 18 | Viewed by 2956

Abstract

The global statistical median behavior of the electron temperature (T_e) in the topside ionosphere was investigated through in-situ data collected by Langmuir Probes on-board the European Space Agency Swarm satellites constellation from the beginning of 2014 to the end of [...] Read more.

The global statistical median behavior of the electron temperature (T_e) in the topside ionosphere was investigated through in-situ data collected by Langmuir Probes on-board the European Space Agency Swarm satellites constellation from the beginning of 2014 to the end of 2020. This is the first time that such an analysis, based on such a large time window, has been carried out globally, encompassing more than half a solar cycle, from the activity peak of 2014 to the minimum of 2020. The results show that Swarm data can help in understanding the main features of T_e in the topside ionosphere in a way never achieved before. T_e data measured by Swarm satellites were also compared to data modeled by the empirical climatological International Reference Ionosphere (IRI) model and data measured by Jicamarca (12.0°S, 76.8°W), Arecibo (18.2°N, 66.4°W), and Millstone Hill (42.6°N, 71.5°W) Incoherent Scatter Radars (ISRs). Moreover, the correction of Swarm T_e data recently proposed by Lomidze was applied and evaluated. These analyses were performed for two main reasons: (1) to understand how the IRI model deviates from the measurements; and (2) to test the reliability of the Swarm dataset as a new possible dataset to be included in the underlying empirical dataset layer of the IRI model. The results show that the application of the Lomidze correction improved the agreement with ISR data above all at mid latitudes and during daytime, and it was effective in reducing the mismatch between Swarm and IRI T_e values. This suggests that future developments of the IRI T_e model should include the Swarm dataset with the Lomidze correction. However, the existence of a quasi-linear relation between measured and modeled T_e values was well verified only below about 2200 K, while for higher values it was completely lost. This is an important result that IRI T_e model developers should properly consider when using the Swarm dataset. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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Other

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13 pages, 2036 KiB

Open AccessTechnical Note

Improved Ionosonde Monitoring of the Sporadic E Layer Using the Frequency Domain Interferometry Technique

by Tongxin Liu, Guobin Yang, Chen Zhou, Chunhua Jiang, Wei Xu, Binbin Ni and Zhengyu Zhao

Remote Sens. 2022, 14(8), 1915; https://doi.org/10.3390/rs14081915 - 15 Apr 2022

Cited by 4 | Viewed by 2040

Abstract

The sporadic E (Es) layer is a thin layer of ion plasma enhancement in the E-region ionosphere, typically at altitudes of 90–120 km with vertical and horizontal extent of several or several tens of kilometers. As the transition region between the lower and [...] Read more.

The sporadic E (Es) layer is a thin layer of ion plasma enhancement in the E-region ionosphere, typically at altitudes of 90–120 km with vertical and horizontal extent of several or several tens of kilometers. As the transition region between the lower and upper atmosphere, this layer is of critical importance for ionospheric studies. The most economical but effective method to observe this layer is using ionosonde, which, however, is incapable of capturing the finer structure or the internal inhomogeneity of the Es layer as the range resolution is on the order of kilometers. To overcome this limitation, we employ the frequency domain interferometry (FDI) technique, a technique that has been successfully applied to the analysis of some radar and sonar measurements. Here, we use the Es layer measurements near Wuhan, China (114°22′E, 30°30′N) on 8 June 2021 as examples to showcase the capability of this technique. Our results show that the spatial resolution of ionosonde imaging is remarkably increased: the complexity of the internal fine structure in the Es layer can be well observed in the FDI-processed ionograms, whereas the intrinsic range resolution is several kilometers. Moreover, by comparing the ionograms obtained with and without the FDI technique, it is found that the FDI-processed ionogram is particularly suitable for the observation of evolutional processes in the Es layer, as well as the identification of different types of Es layer. With this level of spatial resolution, ionosonde, in combination with the FDI technique, opens the possibility for more refined observations of the Es layer. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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12 pages, 18283 KiB

Open AccessTechnical Note

A Method for Automatic Inversion of Oblique Ionograms

by Chunhua Jiang, Cong Zhao, Xuhui Zhang, Tongxin Liu, Ziwei Chen, Guobin Yang and Zhengyu Zhao

Remote Sens. 2022, 14(7), 1671; https://doi.org/10.3390/rs14071671 - 30 Mar 2022

Cited by 6 | Viewed by 2390

Abstract

In this study, a method is proposed to carry out automatic inversion of oblique ionograms to extract the parameters and electron density profile of the ionosphere. The proposed method adopts the quasi-parabolic segments (QPS) model to represent the ionosphere. Firstly, numerous candidate electron [...] Read more.

In this study, a method is proposed to carry out automatic inversion of oblique ionograms to extract the parameters and electron density profile of the ionosphere. The proposed method adopts the quasi-parabolic segments (QPS) model to represent the ionosphere. Firstly, numerous candidate electron density profiles and corresponding vertical traces were, respectively, calculated and synthesized by adjusting the parameters of the QPS model. Then, the candidate vertical traces were transformed to oblique traces by the secant theorem and Martyn’s equivalent path theorem. On the other hand, image processing technology and characteristics of oblique echoes were adopted to automatically scale the key parameters (the maximum observable frequency and minimum group path, etc.) from oblique ionograms. The synthesized oblique traces, whose parameters were close to autoscaled parameters, were selected as the candidate traces to produce a correlation with measured oblique ionograms. Lastly, the proposed algorithm searched the best-fit synthesized oblique trace by comparing the synthesized traces with oblique ionograms. To test its feasibility, oblique ionograms were automatically scaled by the proposed method and these autoscaled parameters were compared with manual scaling results. The preliminary results show that the accuracy of autoscaled maximum observable frequency and minimum group path of the ordinary trace of the F2 layer is, respectively, about 91.98% and 86.41%, which might be accurate enough for space weather specifications. It inspires us to improve the proposed method in future studies. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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9 pages, 3958 KiB

Open AccessTechnical Note

The Prototype of a Fast Vertical Ionosonde Based on Modern Software-Defined Radio Devices

by Alexei V. Shindin, Sergey P. Moiseev, Fedor I. Vybornov, Kseniya K. Grechneva, Viktoriya A. Pavlova and Vladimir R. Khashev

Remote Sens. 2022, 14(3), 547; https://doi.org/10.3390/rs14030547 - 24 Jan 2022

Cited by 7 | Viewed by 3825

Abstract

The description and test results of the prototype of a fast ionosonde for the vertical sounding of the ionosphere, which makes it possible to record ionograms once a second, are presented. Such a high rate of registration of ionograms is required to study [...] Read more.

The description and test results of the prototype of a fast ionosonde for the vertical sounding of the ionosphere, which makes it possible to record ionograms once a second, are presented. Such a high rate of registration of ionograms is required to study the fast processes of redistribution of electron concentration during heating experiments, for registration of fast quasiperiodic and moving ionospheric disturbances in the F, E, and Es layers. The key feature of the presented development is the usage of publicly available radio-electronic components. This provided a significant reduction in the cost of creating the prototype. In the current version, the prototype is based on the software-defined radio (SDR) devices Red Pitaya SDRlab 122-16 and LimeSDR. The test results showed that the quality of the ionograms recorded using the prototype is not worse than the quality of ionograms recorded using the professional CADI ionosonde. The low cost of the components allows providing multi-position registration of ionograms for determination the dynamics of natural and artificial ionospheric disturbances in 3D region of space at a lower expenses rate, as well as to create a network of ionospheric observation points with an increased number of ionosondes. Full article

(This article belongs to the Special Issue Ionosphere Monitoring with Remote Sensing)

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Ionosphere Monitoring with Remote Sensing

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