Search

Regional ionospheric Total Electron Content (TEC) models are most significant to investigate the variability of ionosphere during all-weather conditions. Since the ground-based TEC measurements are not available in oceanic and polar regions, space-based observations are incorporated to increase the positional accuracy and reliability of Global Ionospheric TEC Maps (GIMs). Therefore, data fusion techniques are necessary to enhance the prediction capability of regional ionospheric models by considering multi-source data. In view of this, an attempt is made to investigate Equatorial Ionization Anomaly (EIA) structures in low-latitudinal Indian region using multi-instrument data. Data observations from background model CODEGIM, available International GNSS Service (IGS) stations in India, GNSS receivers at KLEF and Tripura stations, FORMOSAT/COSMIC radio occultation and SWARM during geomagnetic storm period August 26–28, 2021 are used for the study. Spherical Harmonics Function (SHF) of order 4 is employed along with Weighted Least Squares analysis (WLS), where separate weight constraint is computed for each data source. TEC maps of spatial resolution 5° x 5° and temporal resolution of 1 h are generated to illustrate the dynamic behavior of ionosphere. The standard deviation for 3 days is obtained as 0.42, 0.61 and 1.43 TECU respectively. TEC depletions and enhancements are observed on August 27 and 28, with mean values of 12.74 and 15.27 TECU respectively, demonstrating negative and positive storm effects. [ABSTRACT FROM AUTHOR]

Existing ionospheric models perform very well in mapping the calm state of the ionosphere. However, the problem is accurately determining the total electron content (TEC) for disturbed days. Knowledge of the exact electron density is essential for single−frequency receivers, which cannot eliminate the ionospheric delay. This study aims to investigate temporal and spatial variability in the distribution of TEC based on differences between maps of individual Ionospheric Associated Analysis Centers (IAACs) of the International GNSS Service (IGS) and aligned altimetry−TEC from 2005–2021. Based on the temporal distribution, we have observed a significant effect of solar activity on the mean and standard deviation behavior of the differences between global ionospheric maps (GIMs) and Jason−derived TEC. We determined the biases for the entire calculation period, through which it can be concluded that the upcg-Jason and igsg-Jason differences have the lowest standard deviation (±1.81 TECU). In addition, the temporal analysis made it possible to detect annual, semi−annual, and 117-day oscillations occurring in the Jason−TEC data, as well as 121-day oscillations in the GIMs. It also allowed us to analyze the potential sources of these cyclicities, solar and geomagnetic activity, in the case of the annual and semi−annual periodicities. When considering spatial variations, we have observed that the most significant average differences are in the intertropical areas. In contrast, the smallest differences were recorded in the southern hemisphere, below the Tropic of Capricorn (23.5°S). However, the slightest variations were noted for the northern hemisphere above the Tropic of Cancer (23.5°N). Our research presented in this paper allows a better understanding of how different methods of GNSS TEC approximation affect the model's accuracy. [ABSTRACT FROM AUTHOR]

This work presents the potential for using pulsed gas injection to produce amorphous carbon films. In this experiment, the frequency of injecting small amounts of gas was used to control the pressure amplitudes, thus achieving the conditions of plasma generation from stationary, through quasi-stationary, to pulsed oscillations of pressure. In addition, we used various gases and their mixtures, an alternative to argon. In the experiment, we studied the energy state of the plasma. The films were examined for phase and chemical composition, surface morphology, and optical and mechanical properties. We determined low-frequency pulsed gas injections to be conditions favorable for C (s p 3) − C (s p 3) bond formation. The plasma generated by gas injections is better ionized than that generated by static pressure. Pulsed conditions favor the plasma species to retain their kinetic energy, limiting the probability of intermolecular collision events. Since helium has a relatively high ionization energy, it is a practical addition to sputtering gas because of the increasing sp3 content in the films. The electrons created by helium ionization improve the plasma's ionization degree. [ABSTRACT FROM AUTHOR]

The ionospheric corrections quality reflects the residual error between the ionospheric correction and actual ionospheric delay, which is helpful to optimize the stochastic model of GNSS high-precision positioning technologies and shorten the positioning convergence time. However, the quality indicators (QIs) of real-time ionospheric corrections are rarely estimated or provided to users. Satellite-based augmentation systems (SBAS) broadcast real-time ionospheric corrections and the corresponding quality indicator, namely the grid ionosphere vertical error (GIVE), to improve the positioning accuracy and availability of the system. Nevertheless, SBAS provide GIVE estimates of ionospheric corrections for civil aviation tasks requiring meter or sub-meter pseudorange positioning, which is inadequate for high-precision positioning based on carrier phase observations. Thus, based on the traditional algorithm in SBAS, we propose an adaptive GIVE algorithm to monitor the quality of ionospheric corrections in real time by introducing three adjustment coefficients, which makes the GIVE calculation more flexible. An intelligent optimization algorithm, i.e., the Particle Swarm Optimization (PSO) algorithm, is implemented to reduce the computation time and more quickly search for the adjustment coefficients. We use the final Global Ionosphere Map (GIM) products from six Ionosphere Associated Analysis Centers (IAACs) of the International GNSS Service (IGS) to provide ionospheric corrections, while the reference ionospheric delay is extracted from Crustal Movement Observation Network of China (CMONOC) station original observations. The experimental days are chosen considering solar activity, geomagnetic storms, and seasons, and three ionospheric grid points (IGPs) at different latitudes are selected to investigate the performance of the adaptive GIVE algorithm. The results show that the adaptive GIVE algorithm achieves an improvement of at least 46.7% in the ionospheric error bounding performance over the traditional algorithm under all experimental conditions. Moreover, the adjustment coefficients can be used to extrapolate the GIVE values in 2 ~ 3 days during periods of low ionospheric activity, which is significant for real-time GIVE calculations. The root-mean-square (RMS) maps also provided in these final GIMs are used for comparison as the QI of the corresponding corrections, and we find that the GIVE calculated by the adaptive algorithm is more appropriate than these RMS maps to be adopted as the QI of GIMs. [ABSTRACT FROM AUTHOR]

Existing ionospheric models perform very well in mapping the calm state of the ionosphere. However, the problem is accurately determining the total electron content (TEC) for disturbed days. Knowledge of the exact electron density is essential for single−frequency receivers, which cannot eliminate the ionospheric delay. This study aims to investigate temporal and spatial variability in the distribution of TEC based on differences between maps of individual Ionospheric Associated Analysis Centers (IAACs) of the International GNSS Service (IGS) and aligned altimetry−TEC from 2005–2021. Based on the temporal distribution, we have observed a significant effect of solar activity on the mean and standard deviation behavior of the differences between global ionospheric maps (GIMs) and Jason−derived TEC. We determined the biases for the entire calculation period, through which it can be concluded that the upcg-Jason and igsg-Jason differences have the lowest standard deviation (±1.81 TECU). In addition, the temporal analysis made it possible to detect annual, semi−annual, and 117-day oscillations occurring in the Jason−TEC data, as well as 121-day oscillations in the GIMs. It also allowed us to analyze the potential sources of these cyclicities, solar and geomagnetic activity, in the case of the annual and semi−annual periodicities. When considering spatial variations, we have observed that the most significant average differences are in the intertropical areas. In contrast, the smallest differences were recorded in the southern hemisphere, below the Tropic of Capricorn (23.5°S). However, the slightest variations were noted for the northern hemisphere above the Tropic of Cancer (23.5°N). Our research presented in this paper allows a better understanding of how different methods of GNSS TEC approximation affect the model’s accuracy.

This paper presents the experimental results of high-temperature sputtering of nickel targets by the Gas Injection Magnetron Sputtering (GIMS) technique. The GIMS technique is a pulsed magnetron sputtering technique that involves the generation of plasma pulses by injecting small doses of gas into the zone of the magnetron target surface. Using a target with a dedicated construction to limit heat dissipation and the proper use of injection parameters and electrical power density, the temperature of the target during sputtering can be precisely controlled. This feature of the GIMS technique was used in an experiment with sputtering nickel targets of varying thicknesses and temperatures. Plasma emission spectra and current-voltage waveforms were studied to characterize the plasma process. The thickness, structure, phase composition, and crystallite size of the nickel layers produced on silicon substrates were investigated. Our experiment showed that although the most significant increase in growth kinetics was observed for high temperatures, the low sputtering temperature range may be the most interesting from a practical perspective. The excited plasma has the highest energy in the sputtering temperature range, just above the Curie temperature. [ABSTRACT FROM AUTHOR]

Due to the ionosphere delay, which has become the dominant GPS error source, it is crucial to remove the ionospheric effect before estimating point coordinates. Therefore, different agencies started to generate daily Global Ionosphere Maps (GIMs); the Vertical Total Electron Content (VTEC) values represented in GIMs produced by several providers can be used to remove the ionosphere error from observations. In this research, an analysis will be carried with three sources for VTEC maps produced by the Center for Orbit Determination in Europe (CODE), Regional TEC Mapping (RTM), and the International Reference Ionosphere (IRI). The evaluation is focused on the effects of a specific ionosphere GIM correction on the precise point positioning (PPP) solutions. Two networks were considered. The first network consists of seven Global Navigation Satellite Systems (GNSS) receivers from (IGS) global stations. The selected test days are six days, three of them quiet, and three other days are stormy to check the influence of geomagnetic storms on relative kinematic positioning solutions. The second network is a regional network in Egypt. The results show that the calculated coordinates using the three VTEC map sources are far from each other on stormy days rather than on quiet days. Also, the standard deviation values are large on stormy days compared to those on quiet days. Using CODE and RTM IONEX file produces the most precise coordinates after that the values of IRI. The elimination of ionospheric biases over the estimated lengths of many baselines up to 1000 km has resulted in positive findings, which show the feasibility of the suggested assessment procedure. [ABSTRACT FROM AUTHOR]

Single-frequency precise point positioning (PPP) is widely used with the advantage of cost-efficient, while its further development and application are limited by the difficulty of ionospheric delay correction and the long-time convergence, especially for real-time positioning. And the development of high-accuracy ionospheric models plays an important role for the correction of ionospheric delay in single-frequency PPP. In this paper, the final and rapid global ionospheric map (GIM) products released by Chinese Academy of Science (CAS), Center for Orbit Determination in Europe (CODE), European Space Agency (ESA), Jet Propulsion Laboratory (JPL), Universitat Politècnica de Catalunya (UPC), Wuhan University (WHU) and International GNSS Service (IGS) were used as external constraints in static, simulation kinematic and kinematic single-frequency PPP respectively. The performance and practicality of each product were analyzed by using IGS station observation data (September 2017 and January 2018, with different ionospheric activity levels) and a kinematic experiment. The results indicate that GIM products may improve convergence time in most areas of middle and high latitudes of the globe. However, the improvement of convergence time of some regions in low latitudes or near the equator with dense and uniform distributed IGS stations show even better performance than the regions in middle and high latitudes. Comparing with standard PPP (S-PPP), the convergence time of static PPP is reduced about 14–42% and 13–29% with GIM final and rapid products respectively. In simulation kinematic PPP, the convergence time improves 10–43% and 12–25% for final and rapid products respectively. In the kinematic positioning, the addition of external ionospheric constraints may speed up the convergence in the early stage of positioning and improve the accuracy to a certain extent. Among all GIM products, the final products show better performance than that of the rapid products obviously. The GIM products from CAS and CODE and UQRG from UPC express the best performance are recommended to process ionospheric delay in the high-accuracy positioning. [ABSTRACT FROM AUTHOR]

In this work, the Global Ionospheric Maps (GIMs) are used to analyze the behavior of the mid-latitude ionospheric trough (MIT) during the solar cycle 24 (2008–2019). This analysis is performed for the Northern and Southern Hemispheres at different local times: 00, 02 and 04 LT. We study the MIT position dependence on the phase of the solar cycle, seasonal, and geomagnetic activity during the post-midnight period. We find that the MIT position shows an interhemispheric asymmetry. Its equatorward movement from low to high solar activity is about 3 ° and 1 ° for Northern and Southern Hemisphere respectively for the three local times analyzed. There is also a clear seasonal variation, the shift between winter and summer is around 3 ° and 1 ° at 00 LT and 6 ° and 4 ° at 04 LT for the Northern and Southern Hemispheres, respectively. In general, the MIT position reaches the highest geomagnetic latitude in winter, without variation with local time. However, in summer it takes the lowest geomagnetic latitude, moving towards the equator from 00LT to 04LT. The MIT position moves equatorward under disturbed geomagnetic conditions, and the difference between the MIT position during quiet and perturbed days is greater in the Northern than in the Southern Hemisphere. In addition, the periodicity of the variability of the MIT position for both Hemispheres versus the solar wind speed and IMF Bz-component are analyzed using the wavelet transform, showing a clear dependence between them during the descending and minimum solar phase at 13.5 and 27-day time scales. [ABSTRACT FROM AUTHOR]

A new approach is proposed for the global ionospheric modeling using epoch-by-epoch estimation. The GIMs with a high temporal resolution are greatly useful for studying the climatology and weather of the ionosphere, including ionospheric variations, such as noon-time bite-outs and nighttime enhancements.

The aim of this work is the analysis of the mid-latitude ionospheric trough (MIT) using the Global Ionospheric Maps from IGS (GIMs) during the solar minimum, year 2008. This study was performed for different local times, 22, 00, 02 and 04 LT on the Northern and Southern hemisphere simultaneously. In the two hemispheres the MIT show asymmetric pattern. The high-latitude troughs are clearly distinguished in autumn and winter. Another feature is the longitudinal development towards the west of the geomagnetic pole covering a wider area in the Northern Hemisphere. Five empirical reference models were tested and compared with the MIT minimum position obtained from GIMs at different local times for both hemisphere. The results show a better agreement with the observations for the Northern Hemisphere specially with the Köehnlein & Raitt model. Fluctuations of 9 days and 27 days of the MIT minimum position are found, which could be related with the solar wind oscillations, especially for 00 and 02 LT in both hemisphere, suggesting a link between them. [ABSTRACT FROM AUTHOR]

In this study, thin Al2O3 films (11 nm – 82 nm) were deposited by means of a recently developed pulse gas injection magnetron sputtering method and investigated by means of atomic force microscopy, spectroscopic ellipsometry and spectrophotometry. Quite low values of optical constants (1.581 to 1.648 at λ = 550 nm) of the alumina films are directly associated with specific growth conditions (pulse injection of the reactive or reactive + inert gas) in the pulse gas injection magnetron sputtering process. The light transmittance of Al2O3/glass systems (86 % to 90 %) is only a few percent lower than that calculated for glass (93 %). [ABSTRACT FROM AUTHOR]

Abstract: With the expanded application scope of the International GNSS Service (IGS) global ionospheric maps (GIMs), it is of great theoretical significance and practical value to evaluate the quality of IGS ionospheric products. A new methodology is proposed to mosaic ionospheric grid maps, and GIMs‐based solutions for global ionosphere vertical total electron content (VTEC)/Root Mean Square (RMS) eigenvalues are put forward for subsequent quality assessment. Moreover, based on the proposed method and the strategy, it is the first time that the quality of IGS GIMs from a macro perspective is assessed using the extracted daily global maxima of ionosphere VTEC/RMS (1998–2016). The results show that there are some abnormal maxima values in the GIMs data between 1998 and 2004, while products from 2005 to 2016 are of relatively better quality and are suitable for use as follow‐up experimental data. In addition, we analyze the statistical characteristics of spatial and temporal distribution of GIMs‐based VTEC/RMS eigenvalues and the correlation between eigenvalues and solar activity, in order to verify the conformity between ionosphere physics characteristic and eigenvalues statistical properties which is for further data quality assessment of GIMs. By analyzing the spatial distribution of VTEC/RMS maxima and minima, we found that VTEC maxima are located on both sides of the geomagnetic equator and there is a “dual‐hump” phenomenon in the distribution, and VTEC minima are concentrated in the high latitudes, while RMS minima are distributed throughout the globe but RMS maxima in the low latitudes. Meanwhile, in terms of time distribution, VTEC maxima distribute mainly in the local time from 13:00 to 17:00, while VTEC minima are mainly at nighttime; for RMS, the maxima are mostly distributed in the daytime, while the minima are of a slightly higher distribution proportion at night than in the daytime. At the same time, it was found that the eigenvalues, except RMS minima, are strongly correlated with solar activity but there are lags of 2 to 3 days. Consequently, the above statistical characteristics of GIMs‐based VTEC/RMS eigenvalues are in conformity with ionospheric physics. It verifies the availability and reliability of GIMs from a macroscopic perspective and provides a favorable support for the further application and promotion of GIMs. [ABSTRACT FROM AUTHOR]

This paper presents a study of the optical properties and the microstructure of interference Al/Ti/TiO 2 systems obtained by gas injection magnetron sputtering (GIMS). The samples are examined by means of spectroscopic ellipsometry, atomic force microscopy and spectrophotometry combined with colorimetric measurements. The optical constants of the Al, Ti and TiO 2 layers are determined and carefully studied. The thickness of dielectric films varies from 23 nm to 49 nm and directly determines the color of a sample from orange to blue, respectively. The thickness of Ti films ranges from 0 nm to 125 nm which corresponds to both the semitransparent and opaque titanium layers. The colors of the Al/TiO 2 interference systems are not highly saturated because of the high reflectance of aluminum in the visible spectral range. The introduction of a Ti film between Al and TiO 2 reduced the effective amount of reflected light. Moreover, the thickness of the titanium layer is associated with the color saturation of the Al/Ti/TiO 2 multilayered systems. [ABSTRACT FROM AUTHOR]

In this study, thin Al 2 O 3 , SnO 2 and TiO 2 films (37–58 nm) were deposited by means of a recently developed pulse gas injection magnetron sputtering method. The deposition rates are in the range from 1.7 nm/min (for Al 2 O 3 ) to 24.4 nm/min (for SnO 2 ). Atomic force microscopy measurements show that the thus prepared layers are very smooth. The results obtained using scanning electron microscopy and Raman spectroscopy techniques revealed their amorphous-like nature. Optical properties of the dielectrics were examined by means of spectroscopic ellipsometry and show the red-shift of their band-gap energy and lower values of the refractive index compared to corresponding values determined for dense films and/or bulk materials. The microstructural and optical properties of examined oxides are directly associated with specific growth conditions (the impulse injection of the reactive gas) in the pulse gas injection magnetron sputtering process carried out in the low pressure oxygen plasma. [ABSTRACT FROM AUTHOR]

This paper investigates preearthquake ionospheric variations with the use of TEC of Global Ionospheric Maps (GIMs) and regional maps based on Precise Point Positioning (PPP) during the 7.1-M Indonesian earthquake that occurred on November 15, 2014. TEC maps corresponding to 10 days before to 4 days after the event were examined. In addition, a time series of TEC values according to the PPP maps were also evaluated. In addition to GIMs, it was possible to detect TEC variations with PPP maps. The results showed that ionospheric TEC decreased strikingly 4 days prior to the earthquake. This TEC variation was highly likely related to seismic activity. [ABSTRACT FROM AUTHOR]

This paper presents a study of optical and microstructural properties of the TiO 2 /316L, TiO 2 /Ti/316L and TiO 2 /Ti/glass interference systems obtained by gas injection magnetron sputtering technique (GIMS) employing a commercial magnetron line. The samples are examined by means of spectrophotometry, spectroscopic ellipsometry, confocal optical microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. The investigation is completed by colorimetric analysis. Our analysis shows the significant differences in the color of samples with a TiO 2 layer with the thickness of this layer in the range 30–35 nm. [ABSTRACT FROM AUTHOR]

This paper presents a study of the optical properties and the microstructure of semitransparent interference TiO 2 /Ti/glass systems obtained by gas injection magnetron sputtering (GIMS). The samples are examined by means of spectroscopic ellipsometry, spectrophotometry and atomic force microscopy. The investigation is complemented by colorimetric measurements. Optical constants of titanium and titanium dioxide layers are determined and carefully studied. An influence of the deposition time on the thickness of metallic and dielectric films has been found. The thickness of Ti films ranges from 12 nm to 73 nm, while that of TiO 2 films varies from 11 nm to 43 nm. This thickness directly determines the color of a sample from gold to blue, respectively. [ABSTRACT FROM AUTHOR]

This paper describes the influence of the kinetic energy preservation of gas phase particles in coating growing. The model material (TiO 2 ) was synthesized applying two techniques: pulsed magnetron sputtering and, lately developed, gas injection magnetron sputtering. The two deposition methods have allowed the production of coatings in two completely different gas conditions in the vacuum chamber. The phase composition, microstructural, mechanical and optical properties of titanium dioxide coatings are examined by means of atomic force microscopy, confocal optical microscopy, x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy, nanoindentation, spectroscopic ellipsometry and transmittance measurements. The obtained results and performed analysis clearly demonstrate that applying specific gas conditions in the vacuum chamber leads to reduction of gas-phase mutual particle collisions probability, therefore the omission of the bias polarization and/or substrate heating is allowed. [ABSTRACT FROM AUTHOR]

This paper presents a study of the optical properties, microstructure and chemical composition of titanium oxide layers deposited on Ti film using gas injection magnetron sputtering (GIMS). The samples are examined by means of spectroscopic ellipsometry, atomic force microscopy and X-ray photoelectron spectroscopy. The investigation is complemented by colorimetric measurements. The influence of deposition time on the thickness of dielectric layers has been found. A comprehensive analysis of effective dielectric functions of titanium and titanium oxide films is presented. The thickness of titanium oxide film ranges from 13 nm to 54 nm and directly determines the colour of a sample from gold to blue, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Higher peak electron temperature and peak plasma density recorded for the GIMS technique. • Larger content of high temperature TiO 2 polymorph is typical for of GIMS method. • Degree of coatings crystallinity is higher for RMS than for GIMS technique. • Oxidation of titanium taking place entirely at the surface of the magnetron target. • By changing GIMS parameters one can affect thermodynamics of the coating condensation. The aim of the work was to diagnose plasmas excited by two magnetron sputtering techniques: conventional reactive magnetron sputtering (RMS) and magnetron sputtering realized under gas impulse conditions (GIMS) with use of light emission spectroscopy and Langmuir probing. The plasmas were studied during deposition of TiO2 coatings by magnetron sputtering of Ti target in O2 atmosphere. The obtained deposits were investigated with use of infrared spectroscopy (FTIR) and X-ray diffraction (GIXRD). Two major conclusions were drawn from the investigations. One concerned the mechanism of TiO2 formation during reactive sputtering. An absence of emission lines corresponding to plain Ti atoms proves that their oxidation takes place at the surface of the Ti target without any gas phase reactions. The second conclusion concerned deposition thermodynamics. Although the diagnostics of the GIMS plasma revealed a greater plasma density and electron temperature than in the RMS one, it was the latter technique that produced more high temperature polymorph of TiO2. It appears that the pulse technique offers a way to control thermodynamic conditions of deposition in a broad range up to a conversion to the RMS mode of deposition. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this paper is threefold: (1) To present a working methodology for the combined use of modeling technology and microwave remote-sensing measurements in the assessment of attenuation of electromagnetic waves by the vegetation cover; (2) To illustrate this methodology with computer calculations of the attenuation for various soil-plant formations; (3) To give a perspective of the developed methodology applied to the study of global environmental change, including the radiative forcing problem. [Copyright &y& Elsevier]

The multipurpose spectrometer for nondestructive, depth selective investigation of physical and chemical properties of a surface and bulk is described. It realizes opportunities of Mössbauer and X-ray Fluorescence Spectroscopy in normal and TER-conditions, Mössbauer and X-ray diffractometry and also Mössbauer and X-ray Reflectometry. Some analytical characteristics and capabilities of a spectrometer are illustrated as an example of research with a model sample. [ABSTRACT FROM AUTHOR]

• A new approach for global ionospheric modeling with high temporal resolution is proposed. • Global ionospheric maps with high temporal resolution (30 s) are generated. • Several ionospheric anomalies can be clearly seen in the GIMs with high temporal resolution, but not observed by the traditional GIMs with 1-h or 2-h resolution. A new approach is proposed for the global ionospheric modeling using epoch-by-epoch estimation. The GIMs with a high temporal resolution are greatly useful for studying the climatology and weather of the ionosphere, including ionospheric variations, such as noon-time bite-outs and nighttime enhancements. [ABSTRACT FROM AUTHOR]