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

Han Wang,Xiaohua Xu,Jia Luo

doi:10.3390/rs11121419

Han Wang, Xiaohua Xu + Show 1 more

Open Access

https://doi.org/10.3390/rs11121419

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Abstract

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°.

Highlights

In recent years, the global navigation satellite system (GNSS) radio occultation (RO) has become an essential modern technique for observing the Earth’ atmosphere [1,2,3]
No matter whether the constraint on difference in the azimuth of occultation planes (DAOPs) was set for the collocation of RO-derived ionospheric peak parameters (ICPs) or not, the CC (MAB, mean relative bias (MRB), SAB, SRB) between Feng-Yun 3C (FY-3C) RO-derived ICPs and COSMIC RO-derived ICPs was generally higher than that between FY-3C RO-derived ICPs and digisonde-derived ICPs. It indicates that compared with the ICPs derived from digisondes, the FY-3C RO-derived ICPs were more consistent with those derived from COSMIC RO
All the statistical comparison parameters, including CC, mean absolute bias (MAB), MRB, standard deviations of the absolute bias (SDAB), and standard deviations of the relative bias (SDRB), indicated that good consistence existed between the ICPs derived from FY-3C RO and those derived from COSMIC RO, which proves that the ICPs derived from the two RO missions were of similar quality

Summary

Introduction

The global navigation satellite system (GNSS) radio occultation (RO) has become an essential modern technique for observing the Earth’ atmosphere [1,2,3]. The FY-3C RO ionospheric products, including the time and location of the RO events and the corresponding electron density profiles (EDPs), have been provided by the National Satellite Meteorological Centre (NSMC) since 2014, whose quality has been validated in some comparisons with the observations from COSMIC RO mission and digisondes [12,19]. 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]. The performance of RO ionospheric products would degrade where large horizontal electron density gradient exists or when severe ionospheric fluctuation occurs [25]

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