The impact of spherical symmetry assumption on radio occultation data inversion in the ionosphere: An assessment study

Shaikh, Muhammad Mubasshir; Notarpietro, Riccardo; Nava, B.

doi:10.1016/j.asr.2013.10.025

Cited by 15 publications

(17 citation statements)

References 16 publications

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“…The specific values of these ROC values are listed in Table 3, which demonstrates that the ROCs of the two statistical comparison parameters were all positive. Figure 9e-h shows that the minimum values of SDAB and SDRB of FY-3C RO-derived ICPs were all concentrated in the AOP range of 60 • -120 • , which is consistent with the results of Shaikh's simulation study [24]. It is suggested that the spherical symmetry hypothesis should have the least influence on the RO inversion results in this AOP range.…”

Section: The Variation Of the Quality Of Fy-3c Ro-derived Icps With Ssupporting

confidence: 84%

“…What needs to be mentioned is that the AOP is defined as the azimuth at the tangent point of the ray path with respect to the north direction, and the original azimuth angles varied in the range (-180 • , 180 • ). In the present study, following Shaikh et al [24], AOP was reduced to the range of (0 • , 180 • ) considering that for the same location, two occultation directions with the azimuth angle difference of 180 • were actually on the same line of ray path. Figure 3 shows the distributions of the AOPs corresponding to all the qualified FY-3C and COSMIC EDPs during the studied time period.…”

Section: Quality Control Parametermentioning

confidence: 99%

“…The valid value of SEA varied from −90 • to 90 • , but only the non-negative value were used in the following analysis because it is unnecessary to discuss the influence of solar activity during the night. In addition to SEA, the AOP also influences the quality of the RO-derived ionospheric products [23,24].…”

Section: The Variation Of the Quality Of Fy-3c Ro-derived Icps With Smentioning

confidence: 99%

“…COSMIC is the first LEO constellation designed for GNSS RO observations, which has provided more than two million EDPs since it was launched in 2006 [3,6], while digisonde is the traditional technique for measuring the ionosphere status below the peak heights with high accuracy and reliability [20][21][22]. Meanwhile, the most significant error source of RO-derived EDPs is the assumption of the spherical symmetry of the atmospheric refractive index in the inversion process, which means that it is assumed that there is no horizontal gradient of electron density around the spherical shell [23,24]. Therefore, the performance of RO ionospheric products would degrade where large horizontal electron density gradient exists or when severe ionospheric fluctuation occurs [25].…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Ionospheric Peak Parameters Retrieved from FY-3C Radio Occultation: A Statistical Comparison with Measurements from COSMIC RO and Digisondes Over the Globe

Wang

Luo

2019

Remote Sensing

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In this study, two ionospheric peak parameters (ICPs), NmF2 and hmF2, derived from the global navigation satellite system (GNSS) radio occultation (RO) ionospheric electron density profiles (EDPs) obtained by Feng-Yun 3C (FY-3C) mission are compared with those derived from the observations of the Constellation Observing System for the Meteorology, Ionosphere, and Climate (COSMIC) mission and the measurements from 24 digisonde stations distributed around the world during the year from 2014 to 2017. The FY-3C derived ICPs and the COSMIC-derived ICPs are provided by the National Satellite Meteorological Centre (NSMC) and the COSMIC Data Analysis and Archive Center (CDAAC), respectively. The correlation and bias analyses are carried out in the comparison under the collocation criterion with the time interval of 1 h and the space interval of 3° in latitude and 5° in longitude. When comparing the ICPs derived from the two RO missions, the difference in the azimuth of occultation planes (DAOPs) between the matched pairs is limited to be within 20°. The comparison results are analyzed for different solar activity periods, and solar elevation angle (SEA) is taken for the first time as a factor that represents the comprehensive impacts of latitude zones, seasons, and local time of the observations. The results are shown as follows: (1) Both the COSMIC RO-derived and the digisonde-observed ICPs are in good agreement with the FY-3C RO-derived ones. The correlation coefficient (CC) between the NmF2 and hmF2 derived by COSMIC RO and FY-3C RO is 0.965 and 0.916, respectively, while the correlation coefficient between the NmF2 and hmF2 derived by digisonde and FY-3C RO is 0.924 and 0.832, respectively. The quality of FY-3C RO-derived ICPs are reliable enough for further applications. (2) The CC of NmF2 is, in general, higher than that of hmF2 when comparing FY-3C RO with other observations, and the overall MAB and MRB of FY-3C RO-derived ICPs during the higher solar activity period are higher than the ones during the lower solar activity period. The difference between the two RO missions is much smaller than that one between FY-3C RO and digisonde. (3) For a certain solar activity period, the standard deviations of the absolute bias (SDAB) and the standard deviations of the relative bias (SDRB) of FY-3C RO-derived ICPs compared with digisonde-derived ones generally increases with the increase of SEA, while the SDAB and SDRB of FY-3C RO-derived ICPs both get the minimum values for the AOP interval near to 90°.

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Section: The Variation Of the Quality Of Fy-3c Ro-derived Icps With Ssupporting

confidence: 84%

Section: Quality Control Parametermentioning

confidence: 99%

Section: The Variation Of the Quality Of Fy-3c Ro-derived Icps With Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Ionospheric Peak Parameters Retrieved from FY-3C Radio Occultation: A Statistical Comparison with Measurements from COSMIC RO and Digisondes Over the Globe

Wang

Luo

2019

Remote Sensing

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“…The ionospheric electron density was retrieved by the Abel transform of the measured delay of GPS RO signals (Jakowski et al, 2007;Pedatella et al, 2015;Shaikh et al, 2014;Yue et al, 2014). We use three GPS RO measurements: Germany's Challenging Mini-satellite Payload (CHAMP) (Yue et al, 2011), United States' Gravity Recovery and Climate Experiment (GRACE) (Tapley et al, 2004), and the FORMOSAT-3/COSMIC (Syndergaard et al, 2006).…”

Section: Datamentioning

confidence: 99%

The 11 Year Solar Cycle Response of the Equatorial Ionization Anomaly Observed by GPS Radio Occultation

Lin

Bui

et al. 2018

JGR Space Physics

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We have retrieved the latitudinal and vertical structures of the 11 year solar cycle modulation on ionospheric electron density using 14 years of satellite‐based radio occultation measurements utilizing the Global Positioning System. The densities at the crests of the equatorial ionization anomaly (EIA) in the subtropics near 300 km in 2003 and 2014 (high solar activity with solar 10.7 cm flux, F10.7 ≈ 140 solar flux unit (sfu)) were 3 times higher than that in 2009 (low solar activity F10.7 ≈ 70 sfu). The higher density is attributed to the elevated solar extreme ultraviolet and geomagnetic activity during high solar activity periods. The location of the EIA crests moved ~50 km upward and ~10° poleward, because of the enhanced E × B force. The EIA in the northern hemisphere was more pronounced than that in the southern hemisphere. This interhemispheric asymmetry is consistent with the effect of enhanced transequatorial neutral wind. The above observations were reproduced qualitatively by the two benchmark runs of the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. In addition, we have studied the impact of the 11 year solar cycle on the 27 day solar cycle response of the ionospheric electron density. Beside the expected modulation on the amplitude of the 27 day solar variation due to the 11 year solar cycle, we find that the altitude of the maximal 27 day solar response is unexpectedly ~50 km higher than that of the 11 year solar response. This is the first time that a vertical dependence of the solar responses on different time scales is reported.

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An empirical model of the topside plasma density around 600 km based on ROCSAT‐1 and Hinotori observations

et al. 2015

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It is an urgent task to improve the ability of ionospheric empirical models to more precisely reproduce the plasma density variations in the topside ionosphere. Based on the Republic of China Satellite 1 (ROCSAT-1) observations, we developed a new empirical model of topside plasma density around 600 km under relatively quiet geomagnetic conditions. The model reproduces the ROCSAT-1 plasma density observations with a root-mean-square-error of 0.125 in units of lg(Ni(cm À3 )) and reasonably describes the temporal and spatial variations of plasma density at altitudes in the range from 550 to 660 km. The model results are also in good agreement with observations from Hinotori, Coupled Ion-Neutral Dynamics Investigations/Communications/ Navigation Outage Forecasting System satellites and the incoherent scatter radar at Arecibo. Further, we combined ROCSAT-1 and Hinotori data to improve the ROCSAT-1 model and built a new model (R&H model) after the consistency between the two data sets had been confirmed with the original ROCSAT-1 model. In particular, we studied the solar activity dependence of topside plasma density at a fixed altitude by R&H model and find that its feature slightly differs from the case when the orbit altitude evolution is ignored. In addition, the R&H model shows the merging of the two crests of equatorial ionization anomaly above the F 2 peak, while the IRI_Nq topside option always produces two separate crests in this range of altitudes.

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The impact of spherical symmetry assumption on radio occultation data inversion in the ionosphere: An assessment study

Cited by 15 publications

References 16 publications

Ionospheric Peak Parameters Retrieved from FY-3C Radio Occultation: A Statistical Comparison with Measurements from COSMIC RO and Digisondes Over the Globe

Ionospheric Peak Parameters Retrieved from FY-3C Radio Occultation: A Statistical Comparison with Measurements from COSMIC RO and Digisondes Over the Globe

The 11 Year Solar Cycle Response of the Equatorial Ionization Anomaly Observed by GPS Radio Occultation

An empirical model of the topside plasma density around 600 km based on ROCSAT‐1 and Hinotori observations

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