New topside ionosphere model based on Vary-Chap function using radio occultation and topside sounder data

2020 ◽  
Author(s):  
Mengjie Wu
Keyword(s):  
Electron Density ◽  
Radio Occultation ◽  
Satellite System ◽  
Electron Density Profile ◽  
Scale Height ◽  
Topside Ionosphere ◽  
Ionosphere Model ◽  
Ionospheric Models ◽  
Electron Density Profiles ◽  
Global Navigation Satellite

<p><span>The Global Navigation Satellite System (GNSS) radio occultation and topside sounder provide materials for the validation of a mathematical description of the topside ionosphere up to satellite altitude. An attempt to represent the topside electron density profile is using α-Chapman function with a continuously varying scale height. In this study, the Vary-Chap scale height profiles are obtained based on Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) electron density profiles from 1 January 2008 to 31 December 2013 and fitted by a shape function composed of two weighted patterns representing the ion and electron contributions of lower and higher altitudes. The topside profiles of ISIS-1 data are used to define the transition height of different ions. The associated fitting parameters are analyzed to reveal their temporal and spatial features and variations along with enhancement of solar activity. Their prominent dependence on latitudes, longitudes, the local time, the season, and the solar cycle facilitates modeling of the Vary-Chap scale height in constructing empirical topside ionospheric models.</span></p>

scholarly journals Comparison of the characteristics of ionospheric parameters obtained from FORMOSAT-3 and digisonde over Ascension Island

2013 ◽  
Vol 31 (5) ◽  
pp. 787-794 ◽  
Author(s):  
Y. J. Chuo ◽  
C. C. Lee ◽  
W. S. Chen ◽  
B. W. Reinisch
Keyword(s):  
Electron Density ◽  
Radio Occultation ◽  
Peak Height ◽  
Electron Density Profile ◽  
Scale Height ◽  
Activity Period ◽  
Iri Model ◽  
Ascension Island ◽  
Seasonal And Diurnal Variations ◽  
Electron Density Profiles

Abstract. Electron density profile data obtained from the FORMOSAT-3 radio occultation (RO) measurements over Ascension Island are used to study the bottomside thickness parameter B0 in the International Reference Ionosphere (IRI) model, scale height around the F region peak height, and other F2 region parameters. The RO data were collected when the radio occultation occurred at Ascension Island (345.6° E, 8.0° S) during the solar minimum activity period from May 2006 to April 2008. Results show that the B0 values are in moderate agreement with the ground-based observations in the equinox period (correlation coefficient r = 0.682) and winter (r = 0.570), with a strong correlation in summer (r = 0.750). The seasonal and diurnal variations in B0 over Ascension Island show peak values during the daytime and in winter. In addition, the B0 values were underestimated and overestimated in the RO measurements during the daytime and nighttime, respectively. Moreover, the comparison of scale heights shows that scale heights obtained from the retrieved data and digisonde observations are weakly correlation in all three seasons. Furthermore, although the effective scale height (HT) values were reverse of those obtained from the RO measurements and are higher during the nighttime than in the daytime, they are in good agreement with those from ground-based observations. This paper also provides a comprehensive discussion of the effect of the asymmetric ionospheric electron density profiles on RO measurements.

scholarly journals Comparison of ionospheric radio occultation CHAMP data with IRI 2001

2005 ◽  
Vol 2 ◽  
pp. 275-279 ◽  
Author(s):  
N. Jakowski ◽  
K. Tsybulya
Keyword(s):  
Electron Density ◽  
Radio Occultation ◽  
Satellite Orbit ◽  
High Solar Activity ◽  
Satellite Mission ◽  
Density Profiles ◽  
Champ Satellite ◽  
Ionospheric Models ◽  
Routine Basis ◽  
Electron Density Profiles

Abstract. GPS radio occultation measurements on board low Earth orbiting satellites can provide vertical electron density profiles of the ionosphere from satellite orbit heights down to the bottomside. Ionospheric radio occultation (IRO) measurements carried out onboard the German CHAMP satellite mission since 11 April 2001 were used to derive vertical electron density profiles (EDP’s) on a routine basis. About 150 vertical electron density profiles may be retrieved per day thus providing a huge data basis for testing and developing ionospheric models. Although the validation of the EDP retrievals is not yet completed, the paper addresses a systematic comparison of about 78 000 electron density profiles derived from CHAMP IRO data with the International Reference Ionosphere (IRI 2001). The results are discussed for quite different geophysical conditions, e.g. as a function of latitude, local time and geomagnetic activity. The comparison of IRO data with corresponding IRI data indicates that IRI generally overestimates the upper part of the ionosphere whereas it underestimates the lower part of the ionosphere under high solar activity conditions. In a first order correction this systematic deviation could be compensated by introducing a height dependence correction factor in IRI profiling.

scholarly journals Ionosonde total electron content evaluation using International Global Navigation Satellite System Service data

2020 ◽  
Vol 38 (2) ◽  
pp. 347-357 ◽  
Author(s):  
Telmo dos Santos Klipp ◽  
Adriano Petry ◽  
Jonas Rodrigues de Souza ◽  
Eurico Rodrigues de Paula ◽  
Gabriel Sandim Falcão ◽  
...  
Keyword(s):  
Electron Density ◽  
Total Electron Content ◽  
Global Navigation Satellite System ◽  
Satellite System ◽  
Scale Height ◽  
Electron Content ◽  
Navigation Satellite ◽  
Total Electron ◽  
System Service ◽  
Global Navigation Satellite

Abstract. In this work, a period of 2 years (2016–2017) of ionospheric total electron content (ITEC) from ionosondes operating in Brazil is compared to the International GNSS (Global Navigation Satellite System) Service (IGS) vertical total electron content (vTEC) data. Sounding instruments from the National Institute for Space Research (INPE) provided the ionograms used, which were filtered based on confidence score (CS) and C-Level flag evaluation. Differences between vTEC from IGS maps and ionosonde TEC were accumulated in terms of root mean squared error (RMSE). As expected, we noticed that the ITEC values provided by ionosondes are systematically underestimated, which is attributed to a limitation in the electron density modeling for the ionogram topside that considers a fixed scale height, which makes density values decay too rapidly above ∼800 km, while IGS takes in account electron density from GNSS stations up to the satellite network orbits. The topside density profiles covering the plasmasphere were re-modeled using two different approaches: an optimization of the adapted α-Chapman exponential decay that includes a transition function between the F2 layer and plasmasphere and a corrected version of the NeQuick topside formulation. The electron density integration height was extended to 20 000 km to compute TEC. Chapman parameters for the F2 layer were extracted from each ionogram, and the plasmaspheric scale height was set to 10 000 km. A criterion to optimize the proportionality coefficient used to calculate the plasmaspheric basis density was introduced in this work. The NeQuick variable scale height was calculated using empirical parameters determined with data from Swarm satellites. The mean RMSE for the whole period using adapted α-Chapman optimization reached a minimum of 5.32 TECU, that is, 23 % lower than initial ITEC errors, while for the NeQuick topside formulation the error was reduced by 27 %.

scholarly journals Accuracy assessment of the quiet-time ionospheric F2 peak parameters as derived from COSMIC-2 multi-GNSS radio occultation measurements

2021 ◽  
Vol 11 ◽  
pp. 18
Author(s):  
Iurii Cherniak ◽  
Irina Zakharenkova ◽  
John Braun ◽  
Qian Wu ◽  
Nicholas Pedatella ◽  
...  
Keyword(s):  
Electron Density ◽  
Radio Occultation ◽  
Electron Density Profile ◽  
Equatorial Region ◽  
Quality Data ◽  
Quiet Time ◽  
Density Profiles ◽  
Middle Latitudes ◽  
Receiver System ◽  
Electron Density Profiles

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.

scholarly journals Electron density profiles probed by radio occultation of FORMOSAT-7/COSMIC-2 at 520 and 800 km altitude

2015 ◽  
Vol 8 (2) ◽  
pp. 1615-1627
Author(s):  
J. Y. Liu ◽  
C. Y. Lin ◽  
H. F. Tsai
Keyword(s):  
Electron Density ◽  
Density Profile ◽  
Radio Occultation ◽  
System Simulation ◽  
Electron Density Profile ◽  
Abel Inversion ◽  
Simulation Experiments ◽  
Density Profiles ◽  
Satellite Altitude ◽  
Electron Density Profiles

Abstract. The FORMOSAT-7/COSMIC-2 (F7/C2) will ultimately place 12 satellites in orbit with two launches with 24° inclination and 520 km altitude in 2016 and with 72° inclination and 800 km altitude in 2019. In this study, we examine the electron density probed at the two satellite altitudes 500 and 800 km by means of FORMOSAT-3/COSMIC (F3/C) observations at the packing orbit 500 km altitude and mission orbit 800 km altitude, as well as observing system simulation experiments (OSSE). The electron density derived from 500 and 800 km satellite altitude of the F3/C observation and the OSSE confirm that the standard Abel inversion can correctly derive the electron density profile.

scholarly journals On the link between the topside ionospheric effective scale height and the plasma ambipolar diffusion, theory and preliminary results

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Alessio Pignalberi ◽  
Michael Pezzopane ◽  
Bruno Nava ◽  
Pierdavide Coïsson
Keyword(s):  
Electron Density ◽  
Diffusion Theory ◽  
Vertical Gradient ◽  
Electron Density Profile ◽  
Ambipolar Diffusion ◽  
Scale Height ◽  
Topside Ionosphere ◽  
Effective Parameters ◽  
Analytical Functions ◽  
Vertical Scale

Abstract Over the years, an amount of models relying on effective parameters were implemented in the challenging issue of the topside ionosphere description. These models are based on different analytical functions, but all of them depend on a parameter called effective scale height, that is deduced from topside electron density measurements. As their names state, they are effective in reproducing the topside electron density profile only when applied to the analytical function used to derive them. Then, in principle, they do not have any physical meaning. It is the goal of this paper to mathematically link the effective scale height modeled through the Epstein layer to the vertical scale height theoretically deduced from the plasma ambipolar diffusion theory. Firstly, effective and theoretical scale heights are linked through a mathematical relation by showing that they tend to each other in the topside ionosphere. Secondly, their connection is preliminarily demonstrated by calculating effective scale height values from the entire COSMIC/FORMOSAT-3 radio occultation dataset. Thirdly, a possible connection between the vertical gradient of the topside scale height (as obtained by COSMIC/FORMOSAT-3 satellites) and the electron temperature (as obtained by ESA Swarm B satellite) is studied by highlighting corresponding similarities in the diurnal, seasonal, solar activity, and latitudinal variability.

scholarly journals Topside Ionosphere and Plasmasphere Modelling Using GNSS Radio Occultation and POD Data

2021 ◽  
Vol 13 (8) ◽  
pp. 1559
Author(s):  
Fabricio S. Prol ◽  
M. Mainul Hoque
Keyword(s):  
Solar Activity ◽  
Electron Density ◽  
Radio Occultation ◽  
Geomagnetic Latitude ◽  
Low Earth Orbit ◽  
Activity Level ◽  
Topside Ionosphere ◽  
Electron Content ◽  
Total Electron ◽  
Solar Activity Level

A 3D-model approach has been developed to describe the electron density of the topside ionosphere and plasmasphere based on Global Navigation Satellite System (GNSS) measurements onboard low Earth orbit satellites. Electron density profiles derived from ionospheric Radio Occultation (RO) data are extrapolated to the upper ionosphere and plasmasphere based on a linear Vary-Chap function and Total Electron Content (TEC) measurements. A final update is then obtained by applying tomographic algorithms to the slant TEC measurements. Since the background specification is created with RO data, the proposed approach does not require using any external ionospheric/plasmaspheric model to adapt to the most recent data distributions. We assessed the model accuracy in 2013 and 2018 using independent TEC data, in situ electron density measurements, and ionosondes. A systematic better specification was obtained in comparison to NeQuick, with improvements around 15% in terms of electron density at 800 km, 26% at the top-most region (above 10,000 km) and 26% to 55% in terms of TEC, depending on the solar activity level. Our investigation shows that the developed model follows a known variation of electron density with respect to geographic/geomagnetic latitude, altitude, solar activity level, season, and local time, revealing the approach as a practical and useful tool for describing topside ionosphere and plasmasphere using satellite-based GNSS data.

scholarly journals Assessing the quality of ionospheric models through GNSS positioning error: methodology and results

GPS Solutions ◽  
2019 ◽  
Vol 24 (1) ◽  
Author(s):  
Adrià Rovira-Garcia ◽  
Deimos Ibáñez-Segura ◽  
Raul Orús-Perez ◽  
José Miguel Juan ◽  
Jaume Sanz ◽  
...  
Keyword(s):  
Satellite System ◽  
Ionospheric Delay ◽  
Single Frequency ◽  
Positioning Error ◽  
Dual Frequency ◽  
Error Sources ◽  
Ionospheric Models ◽  
Evaluation Metric ◽  
Global Navigation Satellite

Abstract Single-frequency users of the global navigation satellite system (GNSS) must correct for the ionospheric delay. These corrections are available from global ionospheric models (GIMs). Therefore, the accuracy of the GIM is important because the unmodeled or incorrectly part of ionospheric delay contributes to the positioning error of GNSS-based positioning. However, the positioning error of receivers located at known coordinates can be used to infer the accuracy of GIMs in a simple manner. This is why assessment of GIMs by means of the position domain is often used as an alternative to assessments in the ionospheric delay domain. The latter method requires accurate reference ionospheric values obtained from a network solution and complex geodetic modeling. However, evaluations using the positioning error method present several difficulties, as evidenced in recent works, that can lead to inconsistent results compared to the tests using the ionospheric delay domain. We analyze the reasons why such inconsistencies occur, applying both methodologies. We have computed the position of 34 permanent stations for the entire year of 2014 within the last Solar Maximum. The positioning tests have been done using code pseudoranges and carrier-phase leveled (CCL) measurements. We identify the error sources that make it difficult to distinguish the part of the positioning error that is attributable to the ionospheric correction: the measurement noise, pseudorange multipath, evaluation metric, and outliers. Once these error sources are considered, we obtain equivalent results to those found in the ionospheric delay domain assessments. Accurate GIMs can provide single-frequency navigation positioning at the decimeter level using CCL measurements and better positions than those obtained using the dual-frequency ionospheric-free combination of pseudoranges. Finally, some recommendations are provided for further studies of ionospheric models using the position domain method.

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