Ionospheric correction based on ingestion of global ionospheric maps into the NeQuick 2 model.

Xiao Yu,Xinan Yue,Nava Bruno,Jisheng Xu,Ming Ou,Dun Liu,Chengli She,Weimin Zhen

doi:10.1155/2015/376702

Abstract

The global ionospheric maps (GIMs), generated by Jet Propulsion Laboratory (JPL) and Center for Orbit Determination in Europe (CODE) during a period over 13 years, have been adopted as the primary source of data to provide global ionospheric correction for possible single frequency positioning applications. The investigation aims to assess the performance of new NeQuick model, NeQuick 2, in predicting global total electron content (TEC) through ingesting the GIMs data from the previous day(s). The results show good performance of the GIMs-driven-NeQuick model with average 86% of vertical TEC error less than 10 TECU, when the global daily effective ionization indices (Az) versus modified dip latitude (MODIP) are constructed as a second order polynomial. The performance of GIMs-driven-NeQuick model presents variability with solar activity and behaves better during low solar activity years. The accuracy of TEC prediction can be improved further through performing a four-coefficient function expression of Az versus MODIP. As more measurements from earlier days are involved in the Az optimization procedure, the accuracy may decrease. The results also reveal that more efforts are needed to improve the NeQuick 2 model capabilities to represent the ionosphere in the equatorial and high-latitude regions.

Highlights

The ionosphere, the ionized part of the atmosphere extending from ∼60 to several thousand kilometers above the Earth surface, can affect the radiowave signals travelling through it in different ways, such as Faraday rotation, doppler frequency shift, ray path bending, carrier phase advance and pseudorange group delay, and fluctuations of signal intensity and phase [1,2,3,4]
To assess the performance of ionospheric correction based on ingestion of global ionospheric maps (GIMs) into NeQuick 2, the cumulative distribution function (CDF) of total electron content (TEC) error absolute values not exceeding a certain value can be taken as a criterion, which is defined as follows: CDF (x)
An example of cumulative distribution function of TEC errors is given in Figure 7, when Jet Propulsion Laboratory (JPL) GIMs of the previous day are ingested into NeQuick 2

Summary

Introduction

The ionosphere, the ionized part of the atmosphere extending from ∼60 to several thousand kilometers above the Earth surface, can affect the radiowave signals travelling through it in different ways, such as Faraday rotation, doppler frequency shift, ray path bending, carrier phase advance and pseudorange group delay, and fluctuations of signal intensity and phase (ionospheric scintillation) [1,2,3,4]. The slant TEC (sTEC) is defined as the integral of the electron density along the path from the transmitter to the receiver As it is well known, the GNSS single frequency receivers have to compensate for the unwanted term Ig, before solving the navigation equations. Some excellent work about the performance of the Galileo-like model in providing the ionospheric delay predictions has been published [7,8,9,10] In these assessment studies, some IGS stations were used as reference stations to create the broadcast message and the others were used as test stations to obtain the slant TEC mismodeling.

NeQuick 2 Model and Dataset

Ionospheric Correction Algorithm

Results and Discussions

24 TECU 10

Conclusions