Assessment of Corrected Time-Step Methods for Nominal Ionospheric Gradient Calculation: A Comparative Analysis with Spatial Approaches

The effect of ionospheric delay under normal conditions on the Ground-Based Augmentation System (GBAS) can be mitigated by determining the value of the nominal ionospheric gradient (σvig). σvig is generally obtained from Continuous Operating Reference Station (CORS) data using the spatial single difference method (mixed-pair, station-pair, or satellite-pair) or the temporal single difference method (time-step). The time-step method could only use a single receiver but still contains ionospheric temporal variations. We introduce a corrected time-step method using fixed-IPP from the GEO satellite and test it through simulations based on the Global Ionospheric Model (GIM). We also investigate the effect of satellite paths on the corrected time step method in the equator region which tends to be more in a North-South direction and less coverage for East-West ionospheric gradient. This study also addresses the limitations of temporal variation correction coverage and recommends using only the correction from self-observation. All processes are developed under simulation since observation data is still difficult to obtain. Our findings demonstrate that the corrected time-step method yields σvig values consistent with other approaches.