Daily irregularities

In general, high precision real time GNSS positioning techniques, like the so-called Real Time Kinematic or RTK are differential (or relative) techniques. The principle of differential positioning is the following: a fixed reference station, of which the position is precisely known, broadcasts information, called “differential corrections”. These corrections improve the precision of a mobile user position. The closer the mobile user is with respect to the reference station, the more efficient the differential correction is. Indeed, each individual measurement made by a receiver on the signals emitted by a GNSS satellite is affected by satellite and receiver clock errors, atmospheric (tropospheric and ionospheric) propagation delays, multipath, … As both the reference station and the mobile user are observing the same satellites, the RTK technique is based on the assumption that both phase measurements are affected in the same way by the different error sources (except local sources like receiver clocks and multipath). This assumption is valid as long as the distance between the user and the reference station remains “short enough” or in other words, as long as the error sources remain spatially correlated.

Local variability in the ionosphere Total Electron Content due to different “disturbances” (Traveling Ionospheric Disturbances, scintillations, solar flares, geomagnetic storms, …) can pose a threat to real time differential or relative GNSS positioning techniques like RTK.

The University of Liege has developed software which detects in real time such variability in the ionosphere by monitoring TEC high frequency variability at a single station (Warnant et al, 2000).

Warnant R., Pottiaux E. (2000), The increase of the ionospheric activity as measured by GPS, Earth, Planets and Space, 52, 11, pp. 1055-1060.
http://hdl.handle.net/2268/84663