Test flights of GNSS1 at high latitudes

As the first step towards a civilian global navigation satellite system (GNSS) it is proposed to augment the existing GPS system with integrity and ranging signals broadcast by Inmarsat geostationary satellites. This paper presents the results of a flight trial conducted to assess the visibility of these geostationary satellites at the edge of coverage at northern latitudes. The trial was carried out in a DRA BAC 1-11 aircraft in order to assess the use of the satellites for civil airborne navigation. The observed visibility of the geostationary satellites is compared with theoretical simulations, highlighting the reception at the edge of coverage and the effects of the aircraft manoeuvring. The visibility of the geostationary satellites is described with particular emphasis on the approaches and landings. The performance of the GPS system during the trial is also discussed, in terms of accuracy, availability, continuity of service and the ability to provide an integrity capability. Finally, the effects of changing the elevation mask angle and of including the geostationary satellites as ranging sources are examined