Defining the Basis of an Integer-Levelling Procedure for Estimating Slant Total Electron Content

Simon Banville and Richard B. Langley

Abstract:	The determination of slant total electron content (STEC) between GPS satellites and receivers usually implies a “levelling” procedure in which the precise but ambiguous carrier-phase measurements are fitted to the noisy code measurements. It is now recognized that arc-dependent biases, caused by code multipath and inter-frequency bias fluctuations, can introduce errors of up to several TEC units in the levelling process. To overcome this limitation, we present a new levelling procedure based on recent developments in the area of precise point positioning (PPP) allowing for carrier-phase ambiguities to be fixed to integers. The integer ambiguities obtained in the PPP solution are used in a subsequent step to remove the arc-dependency of the geometry-free observations. Using a rigorous mathematical derivation, we show that the resulting observations are still contaminated by receiver- and satellite-dependent biases. Nonetheless, the “integer-levelled” observations are defined with respect to a stable ambiguity datum, as opposed to the variable datum based on inter-frequency code biases. Using co-located receivers, we show that levelling errors can be seemingly eliminated using the “integer-levelled” observations, when carrier-phase ambiguities are fixed to proper integer values in the PPP adjustment. Those results are confirmed by comparing TEC estimates at a day boundary, as computed using independent estimates for the two adjacent days.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	2542 - 2551
Cite this article:	Banville, Simon, Langley, Richard B., "Defining the Basis of an Integer-Levelling Procedure for Estimating Slant Total Electron Content," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 2542-2551.
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