ATMOSPHERIC PERTURBATIONS ON GNSS SIGNALS AND THEIR INFLUENCE ON TIME TRANSFER.

The paper reviews the influence of atmospheric perturbations acting on precise time tranfer applications based on Global Navigation Satellite Systems (GNSS). The Earth atmosphere (ionosphere and troposphere) induces a propagation delay on the signals emitted by GNSS. The tropospheric error can be modelled satisfactorily but the ionosphere remains an important error source. The paper reviews the main disturbances due to the ionosphere and, in particular, shows the influence of solar activity on these disturbances