Transionospheric simulator for polar, auroral and equatorial ionospheres and its use in scintillation prediction and mitigation for GNSS systems.

Global satellite systems, such as GPS, are currently used in many applications to determine accurately the position ( and sometimes also velocity) of the GPS receiver. These signals travel from a GPS satellite at an altitude of about 20,000 km and travel through the ionosphere before arriving at a GPS receiver, typically near the surface of the Earth. The GPS receiver maintains a phase lock on the signal transmitted from the satellite in order to accurately determine the time it has taken the signal to travel from the satellite to the receiver and thus the distance between them. This enables the receiver to find its position from the determined distance to 4 or more GPS satellites. Just as we see stars twinkle due to the effect of the atmosphere so radio signals passing through the ionosphere scintillate . This means that they can show amplitude fades and phase perturbations. When the amplitude becomes very small or when the phase of the signal changes very rapidly and particularly when both occur together, loss of lock of the signal can result which means that the distance of the receiver from the satellite cannot be found. This is particularly the case for 3 specific latitude regions of the Earth: polar, auroral and equatorial. The polar ionosphere has fast moving patches of ionisation, the auroral ionosphere has field aligned sheets extended in longitude ( like an onion skin) and field-aligned cigar-shaped irregularities and the equatorial ionosphere has bubbles of considerably reduced electron density which form and travel upwards after sunset. In this project we will investigate this effect by constructing a model of the propagation path through the background ionosphere with these imbedded irregularities so that we can evaluate their effect for the different regions on the received signal at the GPS receiver for various different conditions, in particular when there is strong scintillation. We will also consider the effect of the scintillation of the received signal on the receiver phase locking and see what conditions have the most severe effect. We will also assess the effect of these scintillations on future satellite positioning systems which will transmit extra frequencies.