Ionospheric and tropospheric delays are considered as an important error source in the Standard Point Positioning (SPP) applications. Empirical models are often applied for correcting these effects from GNSS signals. However, the simulation and forecasting skills of these models are limited due to the simplified model structures and models' sensitivity to the calibration period.

In the AC-GNSS project, a bi-lateral PhD project between Aalborg University and University of Tehran, the novel calibration and data assimilation frameworks to improve the simulation and forecast of atmospheric corrections for SPP applications is studied (doi.10.3390/rs12213545).