A GPS-based method to model the plasma effects in VLBI observations

TL;DR

This paper presents a GPS-based method to estimate and correct ionospheric effects in VLBI observations, improving the accuracy of astrometric measurements by combining GPS TEC data with VLBI delay observations.

Contribution

The paper introduces a novel approach using GPS measurements to model and mitigate ionospheric effects in VLBI data, enhancing observational precision.

Findings

GPS and VLBI ionosphere delay estimates agree within 0.15 ns for intercontinental baselines.

The GPS-based correction reduces ionospheric effects in high-precision VLBI astrometry.

Method successfully applied to 8.4 GHz VLBI data for improved phase delay accuracy.

Abstract

Global Positioning System (GPS) satellites broadcast at frequencies of 1,575.42 MHz (L1) and of 1,227.60 MHz (L2). The dispersive property of the ionosphere can be used to combine independent measurements at the two frequencies to estimate the total electron content (TEC) between a GPS receiver site and a broadcasting satellite. Such measurements, made at sites near to Very Long Baseline Interferometry (VLBI) sites, can be used to estimate the ionospheric contribution to VLBI observables. For our 1991.9 astrometric VLBI experiment in which we obtained group-delay observations in the 8.4 and 2.3 GHz bands simultaneously, we found that the GPS and VLBI determinations of the ionosphere delays agreed with root-mean-square differences below 0.15 ns for intercontinental baselines and 0.10 ns for continental ones. We also successfully applied the GPS-based procedure to reduce the ionospheric effect in phase delays used for high precision differenced astrometry at 8.4 GHz for this same experiment.