SigPerMon

Objectives

Signal and Performance Monitoring (SigPerMon) is a DLR GK project to setup an operational signal and performance monitoring system for GNSS based on data generated by DLR own high gain antennas (30m dish in Weilheim) and world-wide distributed GNSS receiver operated by DLR or IGS. The data and results of SigPerMon shall be made available for DLR internal projects, and supporting the various governmental authorities to support and evaluate Galileo.

Further joined activities are related to the so-called ionospheric threat space (ITS). The ITS related WPs focus on:

• Parameterization and model development for nominal ionospheric behavior in the form of gradient fronts and patches.
• Provision of a plasmaspheric model for the estimation of range delays in the upper atmosphere

The overall aim of the SO collaboration is to support the development of an operational signal and performance monitoring system by including space weather and ionosphere information in real time. The collaboration will improve usability as well as sustainable and safe operation of the European navigation satellite system Galileo. The goals for this analysis service, developed by SO-WWE are:

• to provide expert domain knowledge about the Space Weather impact in GNSS technology (e.g. web site content, discussion and provision of relevant use cases, contribution to validation studies) and the relevant data modelling, data processing and visual data exploration capabilities and methodologies;
• to develop new or tailor already existing IMPC products, tools and services to assess the Space Weather impact on the GNSS performance;
• to provide automated and pre-operational access to relevant Space Weather products, tools and services as provided by the Ionosphere Monitoring and Prediction Center (IMPC);
• to provide a suitable 3d model, describing the electron density from hmF2 up to the GNSS orbit height or above. The model shall be fully described in a TN additionally validated python code (e.g. Unitests) shall be provided.
• to develop suitable parameterized models describing ionospheric gradients and dynamics during nominal and perturbed conditions depending on geophysical conditions.
• to improve the performance of the Galileo single frequency ionosphere broadcast model NTCM G by optimizing Az coefficients for NTCM G

Background

Reliable navigation has become an integral part of our lives today. Hundreds of applications use satellite navigation right down to safety-critical applications such as aircraft landings at visibility levels as low as 0 metres. In this context, it is particularly important to monitor the reliability and quality of the navigation signals, to detect errors promptly, and to make this information available to the applications. For this reason, a system for monitoring satellite signals is to be set up, which will be able to detect deviations from the nominal state of the navigation systems, analyse them and, if necessary, distribute warnings. These activities primarily focus the work on supporting the development and establishment of the European navigation system Galileo, but will in a second stage also capable to analyse the already established systems GPS and GLONASS, and other systems under development worldwide, such as BeiDou/BDS.

The project Signal and Performance Monitoring deals mainly with two points:

• Monitoring of navigation signals at user level
• Analysis error modelling of GNSS signals with the help of high gain antennas

Monitoring of navigation signals at user level

To support routine monitoring of satellite navigation signals for accuracy and integrity, a dedicated GNSS receiver network with real-time data transfer and global coverage will be established and operated. The network should also support the generation of real-time correction data for precise point positioning services. Observations and navigation data from the network will be stored in a long-term archive as a basis for in-depth performance monitoring of signal quality and service quality analysis to provide short- and long-term analysis as well as trends. This will be done not only for Galileo, but also for all global navigation satellite systems. This allows the comparing of the quality of service for Galileo in respect to GPS, GLONASS and BDS.

Signal Analysis using High Gain Antennas

From the data obtained with the GNSS receiver network, a tool has to be developed which evaluates this global data from all existing navigation systems, detect errors at signal level and automatically schedule and controls measurement equipment at high gain antennas such as the 30m antenna in Weilheim to enable more detailed analyses of nominal and abnormal signal states. Based on the combined evaluation of all data, possible errors can then be analysed extremely reliably and with high accuracy and precision and consequently recommendations for the usability of applications can be made. The information on possible errors as well as their effects also makes a significant contribution to the evolution of the European Galileo navigation system.

Modelling the plasmasphere

The ionosphere is the ionized part of the earth’s atmosphere lying between about 50 km and several earth radii whereas the topside ionosphere above about 1000 km height up to the plasmapause is usually called the plasmasphere.

The topside ionosphere has been investigated since the beginning of the development of electron density models to describe the electron density dependence with the altitude. First attempts to represent the topside ionosphere was conducted to extrapolate ionosonde profiles to altitudes above the peak height. Early work shows that a single-layer Chapman function can successfully describe the exponential decay of electron density at the topside. However, with the development of new techniques to observe the upper ionosphere, more robust mathematical functions were developed, such as exponential, parabolic (or sechsquared), Semi-Epstein and further versions of Chapman functions.

Nowadays, after many years of consequent studies, diverse quantitative analytical models have been developed. Examples of valuable models of the plasmasphere are the Carpenter and Anderson model, IZMIRAN plasmasphere model, University of Graz electron density global ionospheric model (NeUoG26), global core plasma model (GCPM27), O’Brian and Moldwi model , Pierrard and Stegen model, and the Neustrelitz electron density model (NEDM30).

Responsibilities

DLR-SO shall provide their knowledge within tasks defined in this project that tackles the expansion and further development of the GNSS signal monitoring system and modelling of the ionosphere. This implies the support for the:

• Conception and content support for Space Weather related KPIs within “GNSS Performance Monitoring”
• Tailoring of IMPC products to define Space Weather related Key Performance Indicators (KPIs)
• IMPC service provision and support of the tailored products and services (e.g. NTRIP broadcaster)

Provision of the three-dimensional plasmasphere model NPSM (Neustrelitz Plasmasphere Model) devel- oped at DLR-SO

In addition to DLR-SO, the following institutes are involved in the project:

• Galileo Competence Center (DLR-GK)