Department of Electronic and Electrical Engineering, University of Bath

The aim of this study is to investigate the performance of a method based on improving the stochastic model to mitigate ionospheric scintillation effects on GNSS positioning by processing experimental data from GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers, which are capable of computing amplitude and phase scintillation parameters from GPS signals. We applied the approach to mitigate ionospheric scintillation effects on GNSS positioning, in conjunction with the estimation of an ionospheric parameter, considered as a stochastic process. This approach produced, in a single epoch point positioning solution, an improvement on height and 3D accuracy of the order of 31% and of 45%, respectively, when applied in a northern high latitude GISTM network under a moderate scintillation scenario. In this project we investigated the case study of 21 November 2009 using data from GISTM stations located in Antarctica and applying the same scintillation mitigation approach to a Precise Point Positioning (PPP) solution. We used an in-house software under development at Unesp. Despite the solar activity being very low, observations from ACE indicated the influence of a recurrent coronal hole high speed stream. Solar wind speed ranged from 430 to 575 km/s, with Bz fluctuations from -8 to +9 nT, generally leading to the formation of ionospheric irregularities responsible of scintillation effects on GNSS signals. Preliminary results from this case study in the PPP mode are encouraging, showing improvements of the order of 26% in 3D accuracy when applying the proposed scintillation stochastic modeling.

Arrays of dual-frequency GPS receivers operating in the Arctic and Antarctic monitor scintillation and ionospheric total electron content at high latitudes. Even under solar minimum conditions, events of significant phase scintillation have been observed in both polar caps. Climatology studies in both hemispheres show that phase scintillation as a function of magnetic local time and geomagnetic latitude primarily occurs in the nightside auroral oval and ionospheric cusp, with the scintillation regions shifting in latitude in response to varying geomagnetic activity. Preliminary results from the first comparative scintillation study supported by ground-based instruments including HF radars, ionosondes and all-sky imagers are presented. In the future, in-situ measurements by the Enhanced Polar Outflow Probe (ePOP) will provide additional support to study the Arctic and Antarctic ionospheres.

In Vietnam, at Hue (16.4°N, 107.6°E) and Hoc Mon (10.9°N, 106.6°E), are located two GPS receivers specially modified for recording, at a sampling rate of 50 Hz, the phase and the amplitude of the L1 signal and the Total Electron Content (TEC) from L1 and L2. In April 2006 both the receivers have observed post-sunset scintillation inhibition when moderate magnetic storms occurred. These measurements together with a 3D plus time imaging of the ionosphere produced by the Multi-Instrument Data Analysis System (MIDAS) have revealed interesting features that will be described in the present paper. MIDAS allows the characterization of the TEC condition over the interested area supporting the speculation on the causes resulting on scintillating GPS signals received at ground. The results confirm the role of the ring current on the generation of the equatorial F layer small-scale irregularities, in relationship with the observed inhibition of scintillations during the storms. The case studies will be discussed also by looking at the different conditions of the Interplanetary Magnetic Field (IMF), to attempt a description of the scintillation effects over a region scarcely investigated in the open literature.