| AVIGA | Accuracy, Visibility, Integrity, Geometry & Availability (of Satellite Navigation Systems) |
| BKG | Bundesamt für Kartographie und Geodäsie |
| BUTE | Budapest University of Technology and Economics |
| CISAS | Centro Interdipartimentale Studi e Attività Spaziali |
| EGNOS | European Geostationary Navigation Overlay Service |
| ESTB | EGNOS System Test Bed |
| EUREF | European Reference Frame (Commission) |
| GALILEA | Galileo Local Elements Augmentation |
| Galileo | Galileo will be Europe's own global navigation satellite system, providing highly accurate, guaranteed global positioning services under civilian control. It will be interoperable with GPS and GLONASS, the other two global satellite navigation systes. Further information is available from the European GNSS Supervisory Authority (GSA), the European Space Agency (ESA) and the European Union (EU). |
| GLONASS | GLObal NAvigation Satellite System - the Russian counterpart to the US GPS system |
| GNSS | Global Navigation Satellite System |
| GPS | Global Positioning System |
| IGS | International GPS System |
| Integrity | Integrity can be defined as a measure of the trust that can be placed in the correctness of the information supplied by the system. Integrity includes the ability of the navigation system to provide users with timely and valid warnings (alerts) when the system must not be used for the intended operation. The integrity performance is usually specified by means of three parameters:
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| Integrity Flag (IF) | A state parameter that informs about the validity of SISA. Since SISA is a prediction, it can not cope with non-predictable phenomena as clock jumps, etc. and consequently it is required the IF to be able to meet the stringent requirement of the “Time to Alarm”. |
| IR | Integrity Risk |
| SISA | Signal In Space Accuracy |
| SISE |
Signal In Space Error. Corresponds to the error at user level caused by the Signal In Space error components. Therefore, it is the real bound of the remaining error in the pseudorange domain at user level caused by the satellite ephemeris errors and the satellite clock errors. |
| SME | Small Medium Enterprise |
| SoL | Safety of Life |