22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-7.6.1

USE OF NAVIGATION SATELLITE SYSTEMS FOR AIRCRAFT OPERATIONS : SENSITIVITY TO ERRORS

J. P. Chauveau , B. Christophe, J. Lacroix
ONERA, Université Paris VI, France

Keywords: satellite navigation, carrier phase measurement errors, ambiguity resolution.

Satellite navigation systems (GPS actually and GNSS in the future) are more and more often called as positioning means and help to aeronautical navigation for all the phases of flight. In geodesy, the use of GPS carrier phase in a differential mode give centimeter precision for localisation. These performances allow to think about a localisation of this type in particular for precision landings. Carrier phase measurement accuracy is of the millimeter order but this measure presents a constant ambiguity corresponding to a whole number of cycles between the satellite and the receiver. To be converted into a distance satellitereceiver, its associated ambiguity has to be determined. Moreover the measures are affected by signal propagation biases and phase noises. Accuracy of orbits and satellite geometry play also a role in the determination of the position. By differencing the measures with the ones coming from a reference station, it is possible to reduce significantly these errors but their levels are still important compared to the wavelength of the signal (around 20 cm). Ambiguity resolution on the fly (AROF) procedures are inspired by methods used in geodesy. For their use on the fly, the short time spans and the necessity of real time do not allow to compensate for all the errors. Depending on the nature and the level of these errors, the methods do not always permit the determination of the good ambiguities, which has an incidence on the integrity and the continuity of service. We propose to give first a quick review of all those errors. Then we’ll study the effects of the most important of them on the positioning given by different methods and we’ll check the utility to fix the ambiguities to integer values.

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