The stability of GPS time and frequency transfer is limited by the fact that GPS signals travel through the ionosphere. In high precision geodetic time transfer (i.e. based on precise modeling of code and carrier phase GPS data), the so-called ionosphere-free combination of the code and carrier phase measurements made on the two frequencies is used to remove the first-order ionospheric effect. In this paper, we investigate the impact of residual second- and third-order ionospheric effects on geodetic time transfer solutions i.e. remote atomic clock comparisons based on GPS measurements, using the ATOMIUM software developed at the Royal Observatory of Belgium (ROB). The impact of third-order ionospheric effects was shown to be negligible, while for second-order effects, the tests performed on different time links and at different epochs show a small impact of the order of some picoseconds, on a quiet day, and up to more than 10 picoseconds in case of high ionospheric activity. The geomagnetic storm of the 30th October 2003 is used to illustrate how space weather products are relevant to understand perturbations in geodetic time and frequency transfer. (C) 2009 COSPAR. Published by Elsevier Ltd. All rights reserved.
Adv. Space Res.ISI Document Delivery No.: 594LZ Times Cited: 1 Cited Reference Count: 23 Pireaux, Sophie Defraigne, Pascale Wauters, Laurence Bergeot, Nicolas Baire, Quentin Bruyninx, Carine Solar and Terrestrial Center of Excellence (STCE) This work has been supported by the Solar and Terrestrial Center of Excellence (STCE, 2009). The authors also acknowledge the IGS for their data and products (IGS data and products, 2009), and the Solar Influences Data Analysis Center (SIDC) for their space weather weekly bulletin products and for their archives on solar events and related indexes (SIDC, 2009). ELSEVIER SCI LTD OXFORD