Ionospheric Monitoring Using "Integer-Levelled" Observations

Simon Banville, Wei Zhang, Reza Ghoddousi-Fard and Richard B. Langley

Abstract:	The global navigation satellite systems (GNSS) are an important component of ionosphere monitoring, since signals travelling from satellites to ground-based receivers allow sampling of the total electron content (TEC) at a multitude of locations simultaneously. Due to the ambiguous nature of the precise carrier-phase observables, it is common practice to fit carrier-phase to code measurements to remove arc-dependent biases. However, this procedure can introduce errors of up to several TEC units in the resulting “levelled” observations, due mainly to code multipath and differential code bias (DCB) fluctuations. Recently, a new procedure termed “integer-levelling” was proposed to eliminate those error sources. This technique uses recent advances in the precise point positioning (PPP) methodology to estimate integer ambiguities for each satellite arc. Those integer ambiguities can then be introduced in the geometry-free carrier-phase observables used in TEC estimation to remove their arc-dependency. Since this procedure does not rely on code measurements, it is independent of code multipath and DCB variations. The resulting slant ionospheric delays still contain (integer) receiver- and satellite-dependent biases. However, it is possible, just like with DCBs, to separate those biases from the quantity of interest by using a mathematical representation of the ionosphere. In this paper, we demonstrate that integer-levelled observations are virtually free from levelling errors when carrier-phase ambiguities are fixed to the proper integer values. As a consequence, vertical TEC (VTEC) values derived from those observations are more coherent between nearby stations. A VTEC map covering Canada also shows smaller surface fit residuals than a map derived from a standard-levelling procedure, although the benefits are not that palpable considering all other error sources involved in the generation of VTEC maps.
Published in:	Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012) September 17 - 21, 2012 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	2692 - 2701
Cite this article:	Banville, Simon, Zhang, Wei, Ghoddousi-Fard, Reza, Langley, Richard B., "Ionospheric Monitoring Using "Integer-Levelled" Observations," Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. 2692-2701.
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