Tomographic imaging of ionospheric plasma bubbles based on GNSS and radio occultation measurements

Total electron content measurements given by the global navigation satellite system (GNSS) have successfully presented results to capture the signatures of equatorial plasma bubbles. In contrast, the correct reproduction of plasma depletions at electron density level is still a relevant challenge for ionospheric tomographic imaging. In this regard, this work shows the first results of a new tomographic reconstruction technique based on GNSS and radio-occultation data to map the vertical and horizontal distributions of ionospheric plasma bubbles in one of the most challenging conditions of the equatorial region. Twenty-three days from 2013 and 2014 with clear evidence of plasma bubble structures propagating through the Brazilian region were analyzed and compared with simultaneous observations of all-sky images in the 630.0 nm emission line of the atomic oxygen. The mean rate of success of the tomographic method was 37.1%, being more efficient near the magnetic equator, where the dimensions of the structures are larger. Despite some shortcomings of the reconstruction technique, mainly associated with ionospheric scintillations and the weak geometry of the ground-based GNSS receivers, both vertical and horizontal distributions were mapped over more than 30° in latitude, and have been detected in instances where the meteorological conditions disrupted the possibility of analyzing the OI 630 nm emissions. Therefore, the results revealed the proposed tomographic reconstruction as an efficient tool for mapping characteristics of the plasma bubble structures, which may have a special interest in Space Weather, Spatial Geodesy, and Telecommunications.Peer ReviewedPostprint (published version

GPS Scintillations and Total Electron Content Climatology in the Southern American Sector

The radio communication and navigation systems can be strongly affected by the ionospheric conditions, which are controlled by solar phenomena associated with radiation variations and solar wind disturbances. These phenomena can generate ionospheric large-scale plasma redistribution and irregularities with scale sizes varying from centimeters to hundred kilometers. These ionospheric irregularities can produce rapid fluctuations in the amplitude and phase of global navigation satellite system (GNSS) signals, degrading the accuracy of GNSS measurements. Here we give a short review of the ionospheric variations associated with solar phenomena, and the actual state of art in the investigations of long-term (seasonal and solar cycle scales) TEC variations and climatology of scintillations, with focus on the southern American sector. It also presented a new TEC calibration procedure when applied to single-frequency PPP

Validation of the α

The α-μ model has become widely used in statistical analyses of radio channels, due to the flexibility provided by its two degrees of freedom. Among several applications, it has been used in the characterization of low-latitude amplitude scintillation, which frequently occurs during the nighttime of particular seasons of high solar flux years, affecting radio signals that propagate through the ionosphere. Depending on temporal and spatial distributions, ionospheric scintillation may cause availability and precision problems to users of global navigation satellite systems. The present work initially stresses the importance of the flexibility provided by α-μ model in comparison with the limitations of a single-parameter distribution for the representation of first-order statistics of amplitude scintillation. Next, it focuses on the statistical evaluation of the power spectral density of ionospheric amplitude scintillation. The formulation based on the α-μ model is developed and validated using experimental data obtained in São José dos Campos (23.1°S; 45.8°W; dip latitude 17.3°S), Brazil, located near the southern crest of the ionospheric equatorial ionization anomaly. These data were collected between December 2001 and January 2002, a period of high solar flux conditions. The results show that the proposed model fits power spectral densities estimated from field data quite well

Analysis of the Regional Ionosphere at Low Latitudes in Support of the Biomass ESA Mission

Biomass is a spaceborn polarimetric P-band (435 MHz) synthetic aperture radar (SAR) in a dawn-dusk low Earth orbit. Its principal objective is to measure biomass content and change in all the Earth’s forests. The ionosphere introduces Faraday rotation on every pulse emitted by low-frequency SAR and scintillations when the pulse traverses a region of plasma irregularities, consequently impacting the quality of the imaging. Some of these effects are due to Total Electron Content (TEC) and its gradients along the propagation path. Therefore, an accurate assessment of the ionospheric morphology and dynamics is necessary to properly understand the impact on image quality, especially in the equatorial and tropical regions. To this scope, we have conducted an in-depth investigation of the significant noise budget introduced by the two crests of the Equatorial Ionospheric Anomaly (EIA) over Brazil and South-East Asia. The work is characterized by a novel approach to conceive a SAR-oriented ionospheric assessment, aimed at detecting and identifying spatial and temporal TEC gradients, including scintillation effects and Traveling Ionospheric Disturbances, by means of Global Navigation Satellite Systems (GNSS) ground-based monitoring stations. The novelty of this approach resides in the customization of the information about the impact of the ionosphere on SAR imaging as derived by local dense networks of ground instruments operating during the passes of Biomass spacecraft. The results identify the EIA crests as the regions hosting the bulk of irregularities potentially causing degradation on SAR imaging. Interesting insights about the local characteristics of low-latitudes ionosphere are also highlighted

Numerical Simulations to Assess ART and MART Performance for Ionospheric Tomography of Chapman Profiles

ABSTRACT The incomplete geometrical coverage of the Global Navigation Satellite System (GNSS) makes the ionospheric tomographic system an ill-conditioned problem for ionospheric imaging. In order to detect the principal limitations of the ill-conditioned tomographic solutions, numerical simulations of the ionosphere are under constant investigation. In this paper, we show an investigation of the accuracy of Algebraic Reconstruction Technique (ART) and Multiplicative ART (MART) for performing tomographic reconstruction of Chapman profiles using a simulated optimum scenario of GNSS signals tracked by ground-based receivers. Chapman functions were used to represent the ionospheric morphology and a set of analyses was conducted to assess ART and MART performance for estimating the Total Electron Content (TEC) and parameters that describes the Chapman function. The results showed that MART performed better in the reconstruction of the electron density peak and ART gave a better representation for estimating TEC and the shape of the ionosphere. Since we used an optimum scenario of the GNSS signals, the analyses indicate the intrinsic problems that may occur with ART and MART to recover valuable information for many applications of Telecommunication, Spatial Geodesy and Space Weather

COMPARATIVE STUDY OF METHODS FOR CALCULATING IONOSPHERIC POINTS AND DESCRIBING THE GNSS SIGNAL PATH

Many efforts have been done in the last decades to improve the formulation of ionospheric models based on data derived from the Global Navigation Satellite System (GNSS). Despite significant improvements in estimating the electron content of the GNSS signal path, little attention has been given to the geometric precision of ionospheric points that describe the signal path. In this work, we show a pioneer comparison about the geometric quality of the ionospheric points using distinct methods. Such analysis was carried out by calculating the GNSS signal path through three methods: a well-known geometric formulation; a new method based on linear approximations; and the used by NeQuick and recommended by the International Telecommunication Union, which was used as reference. As a result, we verified that the mean error of the well-known formulation was about 0.7 km and for the new method was at the level of 10-11 km. Also, the proposed method has the advantage to enable the calculation of ionospheric points for GNSS signals with negative elevation angles. Once negative elevation angles derived from Radio-Occultation techniques are definitively important to improve the geometrical coverage of ionospheric modeling, the proposed technique can be useful in the development of ionospheric modeling processes

COMPARATIVE STUDY OF METHODS FOR CALCULATING IONOSPHERIC POINTS AND DESCRIBING THE GNSS SIGNAL PATH

Abstract: Many efforts have been done in the last decades to improve the formulation of ionospheric models based on data derived from the Global Navigation Satellite System (GNSS). Despite significant improvements in estimating the electron content of the GNSS signal path, little attention has been given to the geometric precision of ionospheric points that describe the signal path. In this work, we show a pioneer comparison about the geometric quality of the ionospheric points using distinct methods. Such analysis was carried out by calculating the GNSS signal path through three methods: a well-known geometric formulation; a new method based on linear approximations; and the used by NeQuick and recommended by the International Telecommunication Union, which was used as reference. As a result, we verified that the mean error of the well-known formulation was about 0.7 km and for the new method was at the level of 10-11 km. Also, the proposed method has the advantage to enable the calculation of ionospheric points for GNSS signals with negative elevation angles. Once negative elevation angles derived from Radio-Occultation techniques are definitively important to improve the geometrical coverage of ionospheric modeling, the proposed technique can be useful in the development of ionospheric modeling processes

A new method for ionospheric tomography and its assessment by ionosonde electron density, GPS TEC, and single-frequency PPP

A new tomographic method was developed with the main goal of mapping the ionosphere in the region of Brazil. The ionospheric background was estimated based on ionosonde and radio-occultation measurements to overcome the lack of data provided by climatological models in low-latitude regions. A new method of performing iterations of the conventional multiplicative algebraic reconstruction technique (MART) was also used in order to avoid nonilluminated cells and improve the spatial resolution. The quality assessment using independent ionosonde data during two weeks in 2013 showed a better performance of the proposed method in comparison to the international reference ionosphere, providing improvements of 31% for the F-layer peak height hm and 24% for the ionospheric peak of electron density Nm. The tomographic technique was also evaluated in the estimation of the total electron content (TEC) and in the single-frequency precise point positioning (PPP). Improvements of 59% in TEC and 31% in the single-frequency PPP were obtained in comparison to the results derived from global ionospheric maps. In addition, a better daily description of the ionosphere was obtained using the proposed method, where it was possible to detect the peak height increasing associated with the prereversal enhancement of the vertical plasma drift that occurs near sunset hours. The results reveal that the modified form of the MART tomographic technique can be considered a useful tool for technical and scientific communities involved in space weather, spatial geodesy, and telecommunications.Peer Reviewe

COMPARATIVE STUDY OF METHODS FOR CALCULATING IONOSPHERIC POINTS AND DESCRIBING THE GNSS SIGNAL PATH

<div><p>Abstract: Many efforts have been done in the last decades to improve the formulation of ionospheric models based on data derived from the Global Navigation Satellite System (GNSS). Despite significant improvements in estimating the electron content of the GNSS signal path, little attention has been given to the geometric precision of ionospheric points that describe the signal path. In this work, we show a pioneer comparison about the geometric quality of the ionospheric points using distinct methods. Such analysis was carried out by calculating the GNSS signal path through three methods: a well-known geometric formulation; a new method based on linear approximations; and the used by NeQuick and recommended by the International Telecommunication Union, which was used as reference. As a result, we verified that the mean error of the well-known formulation was about 0.7 km and for the new method was at the level of 10-11 km. Also, the proposed method has the advantage to enable the calculation of ionospheric points for GNSS signals with negative elevation angles. Once negative elevation angles derived from Radio-Occultation techniques are definitively important to improve the geometrical coverage of ionospheric modeling, the proposed technique can be useful in the development of ionospheric modeling processes.</p></div