Anna Krypiak-Gregorczyk

Observation of the ionospheric storm of October 11, 2008 using FORMOSAT-3/COSMIC data

The electron density profiles retrieved from the COSMIC radio occultation measurements were examined in order to estimate the possibility of its use as additional data source to study changes in electron density distribution occurred during ionospheric storms. The ionosphere behaviour during moderate geomagnetic storm which occurred on October 11, 2008 was analysed. The short-duration positive effect was revealed distinctly in GPS TEC and ionosonde measurements. For the European mid-latitude region it reached the factor of 2 or more relative to the undisturbed conditions. COSMIC data were analyzed and their validity was tested by comparison with ground-based measurements. It was shown the good agreement between independent measurements both in quiet and disturbed conditions. Analysis of COSMIC-derived electron density profiles revealed changes of the bottom-side and topside parts of the ionosphere.

Impact and implementation of higher-order ionospheric effects on precise GNSS applications

High precision Global Navigation Satellite Systems (GNSS) positioning and time transfer require correcting signal delays, in particular higher-order ionospheric (I2+) terms. We present a consolidated model to correct second- and third-order terms, geometric bending and differential STEC bending effects in GNSS data. The model has been implemented in an online service correcting observations from submitted RINEX files for I2+ effects. We performed GNSS data processing with and without including I2+ corrections, in order to investigate the impact of I2+ corrections on GNSS products. We selected three time periods representing different ionospheric conditions. We used GPS and GLONASS observations from a global network and two regional networks in Poland and Brazil. We estimated satellite orbits, satellite clock corrections, Earth rotation parameters, troposphere delays, horizontal gradients, and receiver positions using a global GNSS solution, Real-Time Kinematic (RTK) and Precise Point Positioning (PPP) techniques. The satellite-related products captured most of the impact of I2+ corrections, with the magnitude up to 2 cm for clock corrections, 1 cm for the along- and cross-track orbit components, and below 5 mm for the radial component. The impact of I2+ on troposphere products turned out to be insignificant in general. I2+ corrections had limited influence on the performance of ambiguity resolution and the reliability of RTK positioning. Finally, we found that I2+ corrections caused a systematic shift in the coordinate domain that was time- and region-dependent, and reached up to -11 mm for the North component of the Brazilian stations during the most active ionospheric conditions. .

Ionosphere Model for European Region Based on Multi-GNSS Data and TPS Interpolation

The ionosphere is still considered one of the most significant error sources in precise Global Navigation Satellite Systems (GNSS) positioning. On the other hand, new satellite signals and data processing methods allow for a continuous increase in the accuracy of the available ionosphere models derived from GNSS observables. Therefore, many research groups around the world are conducting research on the development of precise ionosphere products. This is also reflected in the establishment of several ionosphere-related working groups by the International Association of Geodesy. Whilst a number of available global ionosphere maps exist today, dense regional GNSS networks often offer the possibility of higher accuracy regional solutions. In this contribution, we propose an approach for regional ionosphere modelling based on un-differenced multi-GNSS carrier phase data for total electron content (TEC) estimation, and thin plate splines for TEC interpolation. In addition, we propose a methodology for ionospheric products self-consistency analysis based on calibrated slant TEC. The results of the presented approach are compared to well-established global ionosphere maps during varied ionospheric conditions. The initial results show that the accuracy of our regional ionospheric vertical TEC maps is well below 1 TEC unit, and that it is at least a factor of 2 better than the global products.

Carrier phase bias estimation of geometry-free linear combination of GNSS signals for ionospheric TEC modeling

The ionosphere can be modeled and studied using multi-frequency GNSS signals and their geometry-free linear combination. Therefore, a number of GNSS-derived ionospheric models have been developed and applied in a broad range of applications. However, due to the complexity of estimating the carrier phase ambiguities, most of these models are based on low-accuracy carrier phase smoothed pseudorange data. This, in turn, critically limits their accuracy and applicability. Therefore, we present a new methodology of estimating the phase bias of the scaled L1 and L2 carrier phase difference which is a function of the ambiguities, the ionospheric delay, and hardware delays. This methodology is suitable for ionospheric modeling at regional and continental scales. In addition, we present its evaluation under varying ionospheric conditions. The test results show that the carrier phase bias of geometry-free linear combination can be estimated with a very high accuracy, which consequently allows for calculating ionospheric TEC with the uncertainty lower than 1.0 TECU. This high accuracy makes the resulting ionosphere model suitable for improving GNSS positioning for high-precision applications in geosciences.

Integration of multi instrument ionospheric plasma diagnostics used for near Earth environmental modelling

In order to enhance our understanding of the rich plasma physical processes that drives the solar-terrestrial space environment we need to dramatically increase our ability to perform multi point measurements with sensors of different types. The magnetosphere-ionosphere-thermosphere system is strongly affected by electric and magnetic fields, particle precipitation, heat flows and small scale interactions. The changes of the near Earth plasma conditions are produced mainly by natural perturbations, but some of them also have anthropogenic origin. The diagnostics of the ionospheric plasma property as electron and ion density, temperature and velocity can provide essential inputs for modeling the Space Weather conditions. The aim of this presentation is to show global distribution of main plasma parameters during different geomagnetic conditions and seasons diagnosed by various measuring techniques as: in situ wave and plasma diagnostics registered on board of DEMETER satellite, GPS observations collected at IGS/EPN network, GPS observation carried out at the Antarctic and Arctic IGS (International GNSS Service) stations used and the data retrieved from FORMOSAT-3/COSMIC radio occultation measurements. We are willing to present and validate the properties of the ionospheric electron density profiling retrieved from FORMOSAT-3/COSMIC radio occultation measurements. The comparison of radio occultation data with ground-based measurements indicates that usually COSMIC profiles are in a good agreement with ionosonde profiles both in the F2 layer peak electron density (NmF2) and the bottom side of the profiles. For this comparison ionograms recorded by European ionospheric stations (DIAS network) during 2008 year were used. We would like also to discuss the limitation of presented diagnose techniques with respect to different geomagnetic condition and localisation in space.

Investigation of the bottomside / topside contribution to the total electron content at European mid-latitudes

Different radio sounding techniques are used to the study of the ionosphere state. In the given paper analysis of ionospheric electron density and contribution of different parts of the ionosphere to the total electron content (TEC) was carried out on the base of measurements provided by GPS transionospheric sounding, vertical ionospheric sounding and radio occultation (RO). It was considered the region of the European mid-latitudes with 2 closely located ionosonde stations — Pruhonice (50.0 N, 14.6 E) and Juliusruh (54.6 N, 13.4 E). Ionosonde data viz., ionograms, critical frequency of F2 layer (foF2) values and electron density profiles, were provided by European Digital Upper Atmosphere Server (DIAS). To obtain the bottomside ionospheric electron content (IECb) we integrate the bottomside Ne profile derived from digisonde. Topside ionosonde profile, obtained by fitting a model to the peak electron density value, was used to estimate the topside ionospheric electron content (IECt). Also the electron density profiles, derived from FormoSat-3/COSMIC RO measurements, were involved into analysis. The numerical integration was done in order to obtain COSMIC-derived IECb and IECt estimates. Therefore, for the present study the upper limit of the ionosphere has been taken to be at 750–800 km (altitude of COSMIC satellites). The total electron content values were calculated using the observations of the ground-based GPS stations located close to ionosondes. The vertical GPS TEC estimates can be split into two contributions, one part due to the bottomside ionosphere and other part due to the topside ionosphere. The topside part of TEC contains IECt and PEC (plasmaspheric electron content). So, comparison of GPS TEC, F3/C IEC and ionosonde IEC was carried out for different seasonal conditions during period of low solar activity. Special attention was focused on the differences in topside and bottomside parts contribution to TEC for night and daytime hours.