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The global and regional ionospheric maps are often used for a wide range of applications in geosciences, in particular to support precise positioning, but also for geophysical and atmospheric studies. There are currently many analysis centers and research groups providing operational and test VTEC maps. However, IGS ACs and other groups use different mathematical models and estimation techniques resulting different resolutions, accuracies and time delays of their products. Therefore, there is a need to compare and validate existing VTEC models.In this presentation, we present the overview talk about the work within the last 4 years of the IAG Joint Working Group (JWG 4.3.4) on validation of VTEC models for high-precision and high resolution applications. Among others, we evaluated (1) the accuracy and consistency of the IAAC GIMs during high and low solar activity periods of the 24th solar cycle, (2) the accuracy the two most popular ionospheric mapping functions - SLM and MSLM, (3) deterministic and stochastic approaches to VTEC modelling, (4) GIMs performance in single point and precise point positioning GNSS applications, (5) the accuracy and consistency of GNSS-derived VTEC maps and empirical models, (6) GIMs performance using external data (JASON) and GNSS, (7) the accuracy of new global ionosphere models., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

This paper presents a new way of combining Abel inversion and the Chapman model with a linearly increasing scale height to retrieve ionospheric electron density vertical profiles from truncated-sounding radio-occultation data. A linear Vary–Chap model is used to cover the blind region due to data truncation, with parameters estimated by enumeration of the possible values in a grid centered around a set of parameters compatible with ionospheric physics. The resulting electron density is estimated with its corresponding error from the linear least-squares solution presenting the smaller post-fit residual on the input GNSS carrier-phase measurements. The results, tested on a set of representative GNSS RO measurements obtained by COSMIC/FORMOSAT-3, show that this method can retrieve EDVPs with a predominant absolute and relative error of 1010e−m−3 and 5%, respectively, and in less than 10 s per profile, which makes this method suitable for near real-time applications in upcoming missions such as EUMETSAT Polar System-Second Generation.

Three-dimensional (3D) ionospheric imaging at Low-Latitudes is challenging due to the high ionospheric variability and dynamics in the region. The region is characterized by the presence of the Equatorial Ionization Anomaly (EIA), plasma bubbles, layered structures, and strong vertical drifts upwards during the evening pre-reversal enhancement. Aiming to better understand the ionosphere at low latitudes, this study shows the latest developments conducted by the authors to map the region with 3D inversion algorithms based on Global Navigation Satellite Systems (GNSS), ionosondes, GNSS radio-occultation, and empirical models, such as the International Reference Ionosphere (IRI). We address the capabilities of the developed 3D imaging methods to disclose the main morphologies and dynamics of the ionospheric electron density in the region. Limitations are also discussed since data assimilation schemes are still ill-conditioned for a complete 3D reconstruction. Based on the experiments conducted by the authors, the main conclusions have outlined that better 3D representation of the ionosphere in the region of particular interest requires three main improvements: 1) denser GNSS networks on ground and space; 2) better representation by empirical models to be used as background to the inversion technique, mainly to better represent the plasmasphere, topside ionosphere, and during the pre-reversal enhancements; and 3) ionosphere sounding using GNSS or beacon like signals transmitted by Low Earth Orbit (LEO) satellites., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The plasmapause, i.e. the outer boundary of the plasmasphere, is characterised by a sharp electron density gradient. The Neustrelitz ESOC PlasmaPause Model (NEPPM) is a newly developed model of the plasmapause location Lpp. The actual plasmapause positions are derived from the electron density measurements recorded onboard the IMAGE satellite between 2000 and 2005 and the Van Allen probes between 2012 and 2018. An automatic algorithm is developed for detecting plasmapause location along electron density versus altitude profile. The NEPPM model functions are fitted to the Lpp measurements in a least squares sense and model parameters are determined. In our NEPPM approach an ellipse is assumed to describe the principal plasmapause shape in the geomagnetic equatorial plane. This is aligned with the bulge that follows the level of solar activity. Embedded into a 3D approach, the NEPPM allows non-dipole B vectors, providing 3D positions on the plasmapause torus for given latitude, longitude, epoch and Dst. The underlying fitting procedures recreate the varying Lpp as a function of the Dst index and magnetic local time, which gives a better conformity than the GCPM (Global Core Plasma Model).We thank ESOC (ESA/ESOC/OPS-GN) for their active support in developing the model., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

A new ionospheric model called NTCM G (Neustrelitz TEC Model) is now available on the European GNSS Service Centre (GSC) website (https://www.gsc-europa.eu/news/) for correcting ionospheric delay of single-frequency Galileo signals. Investigation shows that NTCM G requires less computing resources compared to the existing reference NeQuick G model while providing a good performance to single-frequency Galileo users. NTCM G does not replace the NeQuick G, but offers an alternative with reduced computational load and complexity for certain users. The NTCM G model was developed by the German Aerospace Centre (DLR) and validated by the Joint Research Centre (JRC) of the European Commission with the support of the European Space Agency (ESA). The description of the source code and its implementation were carried out jointly between DLR and JRC, with the European Union Agency for the Space Programme (EUSPA) and ESA supporting the review and the publication of the model description. The reference implementation of the core algorithm and the auxiliary functions are available for download on the GSC website. The software package provides a portable and validated C/C++ implementation (Matlab and Simulink implementations are also available), including testing functions and testing vectors. NTCM G uses the same Az coefficients broadcast for NeQuick G by the Galileo space segment. Since the Az coefficients are computed in the Galileo ground segment a few hours before the NTCM G works as an ionosphere prediction model for its users.