Global prediction of the vertical total electron content of the ionosphere based on GPS data

Abstract

Although vertical total electron content (VTEC) forecasting is still an open subject of research, the use of predictions of the ionospheric state at a scale of several days is an area of increased interest. A global VTEC forecast product for two days ahead, which is based exclusively on actual Global Positioning System (GPS) data, has been developed in the frame of the International Global Navigation Satellite Systems (GNSS) Service (IGS) Ionospheric Working Group (IGS Iono‐WG). The UPC ionospheric VTEC prediction model is based on the Discrete Cosine Transform (DCT), which is widely used in image compression (for instance, in JPEG format). Additionally, a linear regression module is used to forecast the time evolution of each of the DCT coefficients. The use of the DCT coefficients is justified because they represent global features of the whole two‐dimensional VTEC map/image. Also, one can therefore introduce prior information affecting the VTEC, for instance, smoothness or the distribution of relevant features in different directions. For this purpose, the use of a long time series of final/rapid UPC VTEC maps is required. Currently, the UPC Predicted product is being automatically generated in test mode and is made available through the main IGS server for public access. This product is also used to generate two days ahead preliminary combined IGS Predicted product. Finally, the results presented in this work suggest that the two days ahead UPC Predicted product could become an official IGS product in the near future.

Improved Modeling of Global Ionospheric Total Electron Content Using Prior Information

“…Other scholars have obtained results similarly showing that J2TEC values are larger than the VTEC values derived from GNSS measurements at mid-high latitudes [28,37,44]. In general, the bias among GNSS-derived VTEC maps and J2TEC presented a similar trend, with an average difference of approximately 2 TECU.…”

Prediction of global ionospheric VTEC maps using an adaptive autoregressive model

“…11, the absolute values of bias in low latitudes are smaller than those in mid-high latitudes. Both forecasting VTEC maps and final GIMs are smaller (Mandrake et al 2005;Hernández-Pajares et al 2009;García-Rigo et al 2011). However, the possible reasons for this fact are not clear yet and should be investigated in the future.…”

“…Short-term predictions could be used to generate real-time global VTEC maps (Orús Pérez et al 2010). Along with many other applications, such as automobiles, road mapping, and location-based services, short-term predictions could be used to achieve sub-meter accuracy for mass-market single-frequency receivers (García-Rigo et al 2011).…”

“…The IGS final vertical total electron content (TEC) maps are used for the scientific analysis of the ionosphere and practical applications. However, the IGS final GIM product is released with a time delay of approximately 2 weeks, limiting their application in real-time scenarios, including real-time precise positioning (Shi et al 2012;Rovira-Garcia et al 2015) and space missions, such as the Soil Moisture and Ocean Salinity (SMOS) from the European Space Agency (ESA) (Silvestrin et al 2001;García-Rigo et al 2011). Rapid GIM products, e.g., UQRG (ftp://newg1.upc.es/upc_ ionex) and WHUD (ftp://pub.ionosphere.cn) provided by the Technical University of Catalonia (UPC) and Wuhan University (WHU), respectively, are available with oneday latency.…”

“…Least-squares collocation (LSC) is used by CODE to extrapolate the coefficients of spherical harmonics (SH) for predicting VTEC maps (Schaer 1999). UPC VTEC forecasting is based on the discrete cosine transform (DCT) technique (García-Rigo et al 2011). Moreover, a linear regression module is used to forecast the DCT coefficients and predict VTEC maps.…”