Robust EGNOS Availability Performances under Severe Ionospheric Conditions

Abstract

The estimation of ionosphere delay and associated covariance is the key contributor to reach APV1 and LPV200 availability performance level for EGNOS above the ECAC area. To qualify the future EGNOS system release, ESA has defined a new synthetic data scenario representative of severe ionospheric conditions. In order to be consistent with the real ionosphere behavior, ESA has also defined a new criterion to characterize the dynamics of the gradients, the Along Arc TEC Rate (AATR), that represents the rms over one hour of the particular derivative of the TEC along a path. Typically the value of AATR that is present into the new synthetic scenario is around 2.5 mm per second for L1 at low latitude. To be able to follow such a gradient dynamics Thales Alenia Space France has developed a new Ionospheric Grid Computation module (IGC) to compute the EGNOS ionosphere corrections, in the scope of R&D activities. The IGC module is integrated into SPEED platform, the SBAS Operational Test-bed that fully represents EGNOS Performances in terms of accuracy, continuity, availability and integrity for Safety Of Life services. The outputs of this module is the set of GIVD, the vertical delay, and GIVE, the confidence interval of GIVD at 3.29 sigma, for each Ionospheric Grid Point (IGP). The analyses of the performances of this new ionospheric module have shown a real significant improvement of the APV1 availability performances map (more than 100% of availability performance improvements). These first results show that the compliance to APV1 and LPV200 availability performances can be reached with this solution under severe ionospheric condition.