The medium earth orbit (MEO) radiation hazard is becoming an increasingly important consideration with an ever rising number of satellites missions spending a fraction, or indeed all of their time in this environment. This region lies in the heart of the highly dynamic electron radiation belt, where very large radiation doses can be encountered unless proper shielding to critical systems and components is applied. Significant internal charging hazards also arise in the MEO regime.

The NASA radiation belt AE8 is in almost universal use. However it is well known that there are significant deficiencies in this . The solar cycle dependence in AE8 has been found to be incorrect as well as the energy spectra. Furthermore AE8 is an average and does not provide information on the variability of the radiation environment.

Significant work has been carried out on new empirical as well as physical s, taking into account the temporal, spatial and spectral variations in electron fluxes at altitudes and inclinations relevant for GNSS orbit. ONERA MEO-V2 , based on GPS Navstar and Glonass data, is a new solar cycle dependant specification . It covers energies from 0.28MeV to 2.24MeV. This is included in ECSS-E-10-04C Standard. The environment at MEO is currently extended part of an ESA project* "Energetic Electron Environment s for MEO". The new s covers energies ranging from 0.1MeV to 6MeV at Galileo altitude. *: ESA Contract "Energetic Electron Environment s for MEO" Co 21403/08/NL/JD in consortium with ONERA, QinetiQ, SSTL and CNES

GIOVE-A was launched at the end of 2005 into a representative Galileo orbit carrying two radiation monitors, CEDEX and Merlin.

Designed and built by University of Surrey, the Cosmic-Ray Energy Deposition Experiment (CEDEX) is a low mass, low power instrument providing a detailed LET spectrum for the cosmic-ray ion environment with a pair of large area silicon PIN diode detectors. In addition, CEDEX carries four experimental dose-rate sensors, based on silicon PIN diodes, shielded by domes of thickness 2 mm Al, 4 mm Al, 2 mm Cu and 4 mm Cu.

We present an overview of the CEDEX payload and calibration activities along with an analysis of the radiation environment encountered during the nominal GIOVE-A mission life. The radiation environment as measured by the dose rate diodes was found to be highly dynamic over the period studied, driven by solar-magnetospheric interactions. The mean dose rates encountered on orbit are shown to be within error margins of AE-8 MIN predictions.

A comparison of CEDEX heavy ion LET measurements to s shows a good correlation with CREME-86 90% worst case cosmic ray levels, supported by SEU rates encountered on orbit. A series of SPEs were encountered during the mission lifetime with the corresponding enhanced LET spectrum becoming a good match to flare time predictions.

The Giove-A and -B satellites are tasked with characterising the radiation environment for the Galileo orbit. MERLIN is one of two radiation monitors on Giove-A and SREM is the only environment monitor on Giove-B. Merlin carries two particle telescopes for protons and heavier ions, three electron-current collecting plates and two total dose-sensitive RadFETs. SREM consists of two particle telescopes, for ions and electrons respectively.

MERLIN observations began soon after the Giove-A launch in December 2005 and since April 2008 there has been an overlap with SREM on Giove-B. Results have shown that the Galileo radiation environment is dominated by Space Weather enhancements of electron flux in the outer radiation belt. MERLIN data have been compared to commonly used models for this orbit. Integrated over the Giove-A mission so far, electron and dose data indicate that the electron spectrum has been significantly harder than expected from the AE-8 long-term average and they suggest that the seasonal variation of outer belt enhancements modelled by FLUMIC may need revision for this orbit.

Data from the first few months of SREM observations have shown good agreement with MERLIN and extend the electron measurements to higher energy.

The Space Weather Application Center Ionosphere (SWACI) is a joint project of two DLR institutes - the Institute of Communications and Navigation (IKN) and the German Remote Data Center (DFD). The SWACI project aims to lay the foundations for a space weather center whose services will be focused primarily on ionospheric issues. The project is essentially supported by the German State Government of Mecklenburg-Vorpommern.

The project shall help professionals in the European region, mainly GNSS users, by providing historical data and expert products/services like nowcast, forecast, and alerts on the ionospheric state as well as related space weather issues.

SWACI operates a powerful data processing system working both in real-time and post-processing modes in order to provide actual information to the customers (http://w3swaci.dlr.de). Typical data products include European maps of the Total Electron Content (TEC) and corresponding derivatives such as latitudinal and longitudinal gradients and rate of change, updated every 5 minutes. Space based retrievals include radio occultation data as well as a 3D reconstruction of the topside ionosphere between CHAMP orbit and GPS satellite orbit height.

Recently, the service has considerably improved in different aspects, such as the data base (ground- and space-based), the IT infrastructure, the products and the Web-presentation.

The data base has been extended both with respect to ground- as well as to space-based measurements. The number of available GNSS stations providing data in streaming mode has increased considerably. In addition to the processing of GNSS data, also beacon measurements from various satellites such as NIMS (former NNSS) satellites and COSMIC are received and analysed. Furthermore, we have started to incorporate actual scintillation measurements from a North-European and a South-European station into the service.

Space-based CHAMP data products are extended by including radio occultation measurements onboard GRACE into the SWACI processing system, thus doubling the number of retrieved vertical electron density profiles.

The IT infrastructure has been improved by installing a more powerful data processing unit for computing up to 300 GNSS ground stations in the near-real-time streaming mode.

In order to better fulfil user requirements, new products such as slab thickness, forecast of TEC and TEC perturbations have been developed. They are currently being evaluated. Potential use of these new products for GNSS customers is reported.

The Web-presentation has changed considerably. Whereas the capabilities of the former version were rather restricted, e.g. when considering the availability of historical data, the new portal uses professional solutions of data management including modern forms of data provision.

SWACI is connected to SWENET as data provider as well as user of space weather information to forecast the ionospheric state. In favour of further improving the service, in particular for supporting Galileo applications, enhanced data exchange with SWENET is foreseen.

A major solar disturbance is expected to occur starting around 2011. It is likely to coincide with the launch and availability of the first of the Galileo satellites. The last solar maximum produced major disturbances to the reception of L-Band communications and navigation signals, emanating from satellites. In areas around the geomagnetic equator, periods of several hours, each day, were reported when GNSS would either give no fix at all or, even when differentially corrected, give errors of many tens of metres. Disturbances were also seen in the use of similar equipment at higher latitudes. Much of the problem was put down to GNSS receivers not being agile enough to track through periods of scintillation and the very high levels of refraction found during the height of the solar storms. Tuning of the receiver tracking loop parameters and the adoption of dual frequencies improved matters considerably but this was a fire-fighting approach. With the next solar maximum predicted as being very severe, it would be prudent for receiver manufacturers and operators to know how their receivers are likely to operate during such an event. By using RF signal simulators, we believe that the effects of the high levels of solar activity can be modelled and reproduced to provide a high fidelity facsimile of the RF conditions during a major solar flare. The paper will discuss the parameters that can be simulated and some of the work that is on-going to maximise the fidelity of the simulated GNSS signals under high levels of solar activity.

The use of the GNSS-techniques in high precision positioning applications, e. g. land surveying and machine guidance is increasing very rapidly in the Nordic region. Preparations for the next solar maximum are therefore necessary in order to keep GNSS as an efficient tool that can be relied on.

During the solar maximum 1988-1990, we carried out pilot projects in survey applications. At that time very few L2 receivers were in operation in Sweden.

The last solar maximum 1999 - 2003 coincided with extensive tests of different Network RTK systems. A number of dual-frequency GPS-receivers were in operation in these tests.

Experiences from the two solar maxima and demands for the next maximum will be given in the talk

Aviation uses satellite navigation systems (GNSS - Global Navigation Satellite Systems) for a rapidly increasing number of applications. From initial applications in the en-route phase, to precision approach and landing and including surveillance applications such as ADS-B as well as the synchronisation of communication systems the aviation community is becoming more and more dependent on GNSS for both position and time information.

As an example, ionospheric effects on navigation applications using the different GNSS augmentations, notably space- and ground based, are discussed in this presentation. Three major aviation augmentation systems are currently defined:
ABAS - aircraft based augmentation systems,
SBAS - space based augmentation systems and
GBAS - ground-based augmentation systems

In all three augmentation systems, GNSS receivers are sensitive to loss-of-lock or the inability to capture the low intensity ranging signals under strongly disturbed ionospheric conditions In addition space weather effects on the satellites themselves can reduce signal availability. Lower levels of disturbance may affect the systems as well, but in different ways:

The presence of small-scale structures in the atmosphere (ionosphere and troposphere) can strongly affect the reliability of GNSS high precision real time applications. The concepts of reliability and integrity play a crucial role in the development of Galileo. In particular, small-scale structures in the ionosphere TEC due to Travelling Ionospheric Disturbances or to geomagnetic storms can be the origin of strong disturbances in high precision positioning.

The GALOCAD project has been submitted in response to Galileo Joint Undertaking call for proposals 2423. GALOCAD stands for "GALileo LOCal Component for the Detection of Atmospheric Disturbances which affect high accuracy Galileo applications". The objective of GALOCAD was to develop a methodology for the implementation of a Galileo Local Component for the nowcasting and the forecasting of atmospheric threats (ionosphere and troposphere) which can degrade the "integrity" of high precision Galileo applications.

The paper presents the tools developed in the frame of the project in order to monitor the integrity of GNSS precise real time applications with respect to ionospheric threats and shows in how far these tools could be used to implement real time services for GNSS users.

The objective of our work is to develop an improved real time Total Electron Content (TEC) monitoring technique, which is based on triple frequency Global Navigation Satellite Systems (GNSS) data and whose accuracy will not be affected by code delays (hardware and multipath) anymore. This will allow to improve ionospheric corrections and therefore to increase the precision and reliability of several GNSS navigation and positioning techniques. This paper describes the three steps of the technique which has been fully validated on simulated data and partially on real Giove-A data.

As the third frequency was not yet available at the beginning of our work, we have developed a software allowing to simulate realistic GNSS (GPS and Galileo) measurements on L1,L2 and L5 frequencies. Thanks to this triple frequency simulation software, we are able to test our triple frequency TEC monitoring technique which is divided in three steps. The objective of the first step is to resolve the extra-widelane (EWL) ambiguities. These ambiguities are integer numbers and can be estimated by computing the extra-widelane-narrowlane (EWLNL) combination. The wavelength of the EWLNL combination equals 5.861m for GPS and 9.768m (almost double) for Galileo. The results show that, despite the existence of a residual term, the use of the EWLNL combination allows to resolve the EWL ambiguities, i.e. to fix them at their correct integer values. The objective of the second step is to resolve the widelane (WL) ambiguities. These ambiguities are also integer numbers and are estimated by computing the differenced widelane (DWL) combination. This combination includes the so-called WL and EWL phase combinations and is based on the EWL ambiguities which are considered as resolved from the first step. The wavelength of the DWL combination equals 0.862m for GPS and 0.814m for Galileo. Unfortunately, as the DWL combination also contains a residual term, it is impossible to fix the WL ambiguities at their correct integer values. Nevertheless, the DWL combination gives approximated integer values of WL ambiguities, which are used in the next step. The objective of the third step is to use the results of the first two steps in order to achieve the monitoring of the TEC. Thanks to the availability of triple frequency data we form two independent dual frequency Geometric Free phase combinations. By introducing the values of the EWL ambiguities – resolved in the first step – and the values of the WL ambiguities – approximated in the second step – in those combinations, we only find approximated values of the two remaining unknowns which are TEC values and ambiguities on L2. Nevertheless, using two specific properties concurrently with an estimation of TEC values obtained by the usual dual frequency method, we are able to fix the WL ambiguities at their correct integer values. As a consequence, we obtain the correct integer values of the WL ambiguities and we are able to precisely monitor TEC. This statement has been confirmed by our results.

It is important to note that, as code measurements are only used in the first step of the technique, the precision of the TEC is not affected by code hardware delays neither by code multipath delays. As a consequence, we can expect an improvement of one order of magnitude in regards with the usual dual frequency technique.

Thanks to the availability of real Galileo data from Giove-A satellite, and particularly triple frequency code and phase measurements, we are currently testing our technique on the three-step level. As far as the first step is concerned, the results on real data are in good agreement with those on simulated data. Further validation is ongoing.