The Geodetic Detrending technique: enabling high-accuracy navigation under scintillation

Scintillation is a particular type of space weather perturbation occurred when the signals from the Global Navigation Satellite System (GNSS) traverse irregularities in the ionosphere; the upper layer of the Earth atmosphere. This produces rapid variations on the refraction index and, when the size of the irregularities is close to the Fresnel length of the frequencies used in GNSS frequencies, can also produce diffractive effects affecting the signal amplitude and the tracking of the carrier-phase measurements. Under these conditions, techniques delivering a High Accuracy Service (HAS) are severely degraded in terms of positioning accuracy and availability. The research group of Astronomy and Geomatics has recently introduced the Geodetic Detrending to perform scintillation studies. The GD method removes slowly-varying effects (i.e., trends) in the GNSS signals, such as the satellite movement, the on-board atomic clock offset, and the tropospheric delay (the atmosphere layer from sea level up to 50 km in height). Once the trends are removed, the GD technique allows studying effects of shorter time-scale -rapid fluctuations-of the GNSS signals, with the focus on the identification and correction of discontinuities, the so-called “cycle-slips”, on the geodetically de-trended GNSS carrier-phase measurements. Ultimately, once the cycle-slips problem is mitigated, the HAS can be re-stored under scintillation conditions.