Verifying EGNOS integrity in practice: GIMAT — a tool based on statistical Extreme Value Theory

With the advent of augmentation systems such as WAAS and EGNOS, satellite navigation gets more and more used for so-called Safety of Life (SoL) applications, with civil aviation being the most prominent example. The integrity of the position solution resulting from the satellite navigation signals is crucial, but difficult to test due to the extremely small probabilities involved. To overcome this problem statistically advanced techniques can be applied to GNSS integrity verification, based on the Extreme Value Theory (EVT), which enable extrapolation of the observed distribution's tail into the non-integrity domain. The Netherlands Space Office has funded the development of a software tool, named GIMAT, based on these EVT algorithms, which is currently completed and being used in practice. Almost two months EGNOS data has been tested using GIMAT, which showed EGNOS to be compliant with ICAO requirements.