Effects on Satellite Navigation

Kurzfassung

Electromagnetic radio waves transmitted from satellites of Global Navigation Satellite Systems (GNSS) such as GPS, GLONASS or GALILEO interact with the ionospheric plasma on their path to the receiver, changing their speed and direction of travel. At the commonly used L-band frequencies (between 1.2 and 1.6 GHz), the ionosphere causes signal delays that correspond to range errors of up to 100 meters. In a first order approximation the range error is proportional to the integral of the electron density along the ray path (Total Electron Content - TEC) and can be mitigated by a simple linear combination of the navigation signals at two different frequencies. However, horizontal gradients in the ionospheric ionisation and ionospheric irregularities producing phase fluctuations and radio scintillations may significantly degrade navigation signals up to loss of lock. Strong TEC gradients, Travelling Ionospheric Disturbances (TIDs) and phase fluctuations are often correlated with space weather phenomena such as geomagnetic/ionospheric storms. Depending on the user requirements, the current GNSS technology takes into account space weather effects by developing proper mitigation techniques. Thus, space weather effects can be reduced but cannot be completely removed. Uncertainties remain in particular in case of strong and highly dynamic ionospheric plasma density irregularities. Therefore, to fulfil growing safety requirements in GNSS applications, the impact of the ionospheric plasma on GNSS applications has to be studied in more detail. Fortunately, the GNSS technique itself provides a unique opportunity for high resolution monitoring the ionosphere on global scale.