Method and system for determining an error in the estimation of the time taken to cross the ionosphere

A method for determining an error in the estimation of the time taken to cross the ionosphere by a signal along a vertical sight axis associated with a receiver, the said vertical sight axis cutting the ionosphere at a point of interest, the vertical sight axis being an axis passing through the receiver and a satellite of interest, the method comprising:

• a first step of determining at least two points of cutting of the ionosphere by two sight axes between a satellite and at least two ground stations or a ground station and at least two satellites;
• a second step of determining at least one angle formed by a segment going from the said point of interest to one of the said cutting points and by a segment going from the said point of interest to another of the said cutting points;
• a third step of determining the spatial dispersion of the said cutting points with respect to the said point of interest on the basis of the said angle, by finding the difference with a predetermined angle and taking the average of the said difference or of the said differences;
• a fourth step of determining an error in the estimation of the ionosphere crossing time by addition:
• of a first error in the estimation of the crossing time dependent on a variance calculated by interpolation on the basis of a TRIN model,
• to a second error in the estimation of the crossing time dependent on the said spatial dispersion.