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The differential code bias (DCB) of the Global Navigation Satellite Systems (GNSS) receiver should be precisely corrected when conducting ionospheric remote sensing and precise point positioning. The DCBs can usually be estimated by the ground GNSS network based on the parameterization of the global ionosphere together with the global ionospheric map (GIM). In order to reduce the spatial-temporal complexities, various algorithms based on GIM and local ionospheric modeling are conducted, but rely on station selection. In this paper, we present a recursive method to estimate the DCBs of Global Positioning System (GPS) satellites based on a recursive filter and independent reference station selection procedure. The satellite and receiver DCBs are estimated once per local day and aligned with the DCB product provided by the Center for Orbit Determination in Europe (CODE). From the statistical analysis with CODE DCB products, the results show that the accuracy of GPS satellite DCB estimates obtained by the recursive method can reach about 0.10 ns under solar quiet condition. The influence of stations with bad performances on DCB estimation can be reduced through the independent iterative reference selection. The accuracy of local ionospheric modeling based on recursive filter is less than 2 Total Electron Content Unit (TECU) in the monthly median sense. The performance of the recursive method is also evaluated under different solar conditions and the results show that the local ionospheric modeling is sensitive to solar conditions. Moreover, the recursive method has the potential to be implemented in the near real-time DCB estimation and GNSS data quality check. [ABSTRACT FROM AUTHOR]

The equivalent slab thickness of the ionosphere is defined by the ratio of the vertical total electron content and the peak electron density. The equivalent slab thickness provides an easy measure of the width or shape of vertical electron density profiles which are very sensitive to temperature and composition changes in the thermosphere and to plasma redistribution processes. In this talk we present a long term trend analysis of the equivalent slab thickness of the ionosphere. The analysis is made for several vertical sounding stations located in Europe and covers the solar cycles 23 and 24. As our studies have shown, the negative long-term trend of the equivalent slab thickness during solar cycle 23 range from about 11 up to 62 km/decade indicating a significant thermospheric cooling since 1995 when the observations started. We discuss these observations and related physics in the light of additional data covering the years 2010-2018. Our investigation shows that measurements of the equivalent slab thickness of the ionosphere can essentially contribute to monitor and better understand long term changes in the thermosphere-ionosphere systems. [ABSTRACT FROM AUTHOR]

Perturbations in the ionosphere are of great interest not only for scientific research, but also for applications using transionospheric radiosignals (e.g. GNSS applications and HF communication), because the transmission of radiosignals is sensitive to the electron density in the ionosphere. However, ionospheric perturbations have manifold character. Their spatial range can vary between global and very local effects (a few hundreds of km range) and their temporal range varies between seconds and days. All these perturbations have different physical background and different impact on applications. Many ionosphere perturbation indices that characterize the state of ionospheric perturbations have been introduced in the past (e.g. ROTI, S4, σ Phi , AATR, R eff , W-index, SISTED, SOLERA, DIXSG, IBI, Dfu/Dfl, etc.). This manuscript is an assessment of a subset of diverse ionospheric indices developed and/or applied in Europe. It describes the objectives of the indices, demonstrates their character in a case study for September 2017, indicates their applicability for different use cases in science and industry and guides users to find the appropriate index for their purposes. [ABSTRACT FROM AUTHOR]