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In times of highly precise and increasingly autonomous GNSS applications, the influence of space weather on their system performance is increasingly becoming the focus of current research and development. The complex monitoring and research of space weather in its variety of phenomena and with its effects, for example in satellite technology, aerospace, telecommunications and navigation, is an increasingly important mission.The DLR Institute for Solar-Terrestrial Physics in Neustrelitz is investigating the influence of space weather on both critical systems and services such as GNSS or RF communications, as well as ground- and space-based infrastructures such as power grids or satellites. Of outstanding importance is the efficient implementation of the interfacing between the increasing scientific expertise and the most diverse user requirements from the national and international public and private sectors, academia and industry.As an essential core component of this interface, the working group "Pre-operational Services" develops and operates the "Ionosphere Monitoring and Prediction Center (IMPC)" in cooperation with the "German Remote Sensing Data Center" of the DLR. With its special combination of scientific know-how on GNSS based remote sensing and modelling of the ionopshere, instrumentation (e.g. high rate GNSS receiver network, Global Ionospheric Flare Detection System (GIFDS), Callisto) and the use of state-of-the-art data processing technologies, the IMPC contributes significantly to monitoring the impact of space weather on today's technologies in near-real time and to avoiding or reducing it through the application of a wide range of products and services.This contributionwill present IMPC's pre-operational services and their incorporation into relevant national and international networks (e.g. NOAA-SWPC RTSW, ESA S2P, PECASUS). Furthermore, the unique instrumentation, applied technology approaches and already developed and planned products and services will be presented.

This work shows a 20-month statistical evaluation of different Total Electron Content (TEC) estimators for the Central and South America regions. The TEC provided by the International GNSS Service (IGS) in the area covered around the monitoring GNSS stations are used as reference values, and they are compared to TEC estimates from the physics-based (Sheffield University Plasmasphere Ionosphere Model—PIM) and the empirical (Neustrelitz TEC Model-Global—NTCM-GL) models. The mean TEC values show strong dependence on both solar activity and seasonal variation. A clear response was noticed for a period close to 27 days due to the mean solar rotation, as seen in the solar flux measurements. Consistently, the mean TEC values present an annual variation with maxima during December solstices for southern stations with geographic latitudes greater than 25 S. Semi-annual dependence has been observed in TEC for the sector between 25 of geographical latitude but with modulations caused by fluctuation in the solar radiation. We observed a high correlation between solar radio flux F10.7 and NTCM-GL outputs. The fast increases in F10.7 index have caused significant differences between IGS data and NTCM-GL results mainly for equatorial and low latitudes. For the initial months of the evaluated period (January–April, 2016), the errors of the physics-based model were considerably larger, mainly near the equatorial ionization anomaly. The discrepancies observed in SUPIM results are mainly due to inputs of solar EUV flux. The EUVAC model has underestimated EUV flux between January and April, 2016, when the solar activity was moderated and Solar2000 model has overestimated such flux during low solar cycle period between May and August, 2017. In relation to IGS data, the two assessed models presented smaller differences during the June solstice season of 2016.

Strong solar radio bursts are known to cause radio interference and have the potential to affect satellite radio systems such as Global Navigation Satellite System (GNSS). On September 6, 2017, GNSS signal interferences were observed at ground stations in the European sector from the low to high latitudes for all GNSS satellites in view including GPS, GLONASS and Galileo. This paper studies the GNSS signal response to the solar radio burst events. The impact of the radio burst has been found at GNSS L2/L5 (1.2 GHz) frequencies, but not at L1 frequency (1.4 GHz). The ground observation of the solar radio spectrum corresponds well to such frequency dependence. The signal interference reduces the signal to noise ratio and it is characterized by the amplitude scintillation index, showing clear difference between the signal interference patterns and other background noises. We examine the receiver performance for this event and the result show a clear indication of frequency-dependent GNSS performance degradation during strong space weather.

Trans-ionospheric radio signals of global navigation satellite systems (GNSS) like GPS, GLONASS, and GALILEO may suffer from rapid and intensive fluctuations of their amplitude and phase caused by small scale irregularities of the ionospheric plasma. Such disturbances occur frequently during the evening hours in the equatorial region due to plasma flow inversion causing Plasma bubbles or during geomagnetic storms in the polar region. This phenomenon, which is called radio scintillation, can strongly disturb or even disrupt the signal transmission. We investigate the effect of small scale ionospheric irregularities on Global Navigation Satellite System (GNSS) positioning using an Experimentation and Verification Network (EVNet). The EVNet is a high rate GNSS receiver network for scintillation measurement from high latitudes down to equatorial region operated by DLR. We will inform about the recent status of the EVNet as well as its recent and future development. We will inform about new equipment used and present related research. Therefore we will present analysis results obtained primarily from two equatorial high rate EVNet GNSS receiver stations designed and operated by the German Aerospace Center (DLR) in cooperation with Bahir Dar University (BDU) at 11.6N, 37.4E. Both receivers collect raw data sampled at up to 50 Hz, from which characteristic scintillation parameters such as the S4 index are deduced. Both stations are located close to one another and aligned in an east west, direction which allows us to estimate the zonal drift velocity and spatial dimension of equatorial ionospheric plasma irregularities. Therefore, the lag times of moving electron density irregularities and scintillation patterns are derived by applying cross correlation analysis to high-rate measurements of the slant total electron content (sTEC) and to the associated signal power, respectively. Finally, the drift velocity is derived from the estimated lag time, taking into account the geometric constellation of both receiving antennas and the observed GPS satellites. Furthermore, we will show EVNet capabilities for space weather research and service as well as for other possible uses and investigations.

Radio signals transmitted by modern communication, nav- igation and Earth observation systems are influenced during propagation through the ionosphere. The ionosphere is an ionoized layer ranging from about 50 km till 1000 km around the earth and is mainly generated by the solar irradiance. The strong dependence on geographical, diurnal, seasonal, solar cycle and space weather effects lead to strong dynamical ionospheric variations and causes problems for reliable modelling and related applications. During the past decades a growing number of observations are available with the potential to significanly improve monitoring and modelling of the ionosphere. Especially ground- and space-based Global Navigation Satellite System (GNSS) data provide a significant contribution for our understanding of the ionosphere, but also for improving operations and performance of telecommunication and navigation systems. GNSS based ionospheric products provided via ESPAS help to understand the ionosphere and its interaction with extreme space weather conditions.

Ionospheric perturbations can have a strong influence on the use of global navigation satellite systems (GNSS) and other space-based systems. The detection and estimation of spatial and temporal variations of electron density in near real-time is challenging and subject to current research. Based on former studies on the Disturbance Ionosphere Index (DIX) [1], here we present preliminary results concerning its capability to deduce also directional information on horizontal structures of the ionospheric electron content. Related results are derived from GNSS data sets obtained over Europe during a moderate ionospheric storm in October 2011. Although being limited due to the uneven data coverage over Europe, the derived index indicates the potential of providing valuable information on the actual performance of GNSS applications. The index is designed to be reliable and robust and allows an easy and objective interpretation. The calculation of the ionospheric disturbance index is based on the Total Electron Content (TEC) which has been confirmed in many publications to be an outstanding parameter for quantifying the range error and the strength of ionospheric perturbations. The quality of the index is dependent on the density of the used GNSS data base. The shown analysis results are calculated using the IGS and EUREF GNSS reference networks. DIX shall be made available to registered users in near real-time via the Ionospheric Monitoring and Prediction Center (IMPC) just established at DLR (http://impc.dlr.de).

Temporal and spatial gradients in the ionosphere can cause major threats on communication and navigation satellite systems, because the propagation of transionospheric radio signals is influenced by the ionospheric electron content. Space weather events are often the source of strong ionospheric disturbances. Forecasting ionospheric perturbations related to space weather events is therefore a crucial task being of special interest for GNSS users. The climatology of ionospheric storms seen in the Total Electron Content (TEC) over Europe as a response of the ionosphere towards Earth oriented space weather events is well known. It depends on season, elapsed time from event arrival, location and local time. However, the deviation of a single storm to the mean behavior can be large. A good correlation between strength of the ionospheric storm, i.e. the maximum deviation of the TEC to 27 day median, to solar wind or geomagnetic activity indices is hard to define. Hence forecasting TEC for disturbed conditions is a challenging task. However, the storm climatology and comprehensive correlation studies allow forecasting of the most probable TEC perturbation amplitude for the European region. GNSS users are in need of information about arriving threads due to space weather events as early as possible. Therefore, an Early Warning message for GNSS users has been developed at the DLR within the FP7-Project AFFECTS. It provides information about Earth endangering space weather events to interested GNSS users up to two days before their arrival. Additional information are now added by a second warning message distributed thirty minutes before arrival at Earth giving more specific information like exact arrival time, forecasts of geomagnetic indices, approximate TEC perturbation and range error for the European region. An overview on the Early Warning for GNSS user service provided by DLR is presented in this paper.