Influence of ionospheric perturbations in GPS time and frequency transfer

TL;DR

This paper examines how residual second- and third-order ionospheric effects influence GPS-based geodetic time transfer, finding third-order effects negligible and second-order effects causing small timing errors, especially during high ionospheric activity.

Contribution

It provides an analysis of residual ionospheric effects on GPS time transfer, highlighting the significance of second-order effects during space weather disturbances.

Findings

Third-order ionospheric effects are negligible.

Second-order effects can cause timing errors up to 10 picoseconds during high activity.

Space weather impacts are relevant for precise GPS time transfer.

Abstract

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.