Ionospheric models and measurements for common-view time transfer

We discuss technologies for estimating ionospheric delays in Global Positioning System (GPS) common-view time transfer. Such technologies include the broadcast Klobuchar ionospheric model, the use of ionospheric maps from the International GPS Service (IGS), codeless techniques for the measurement of the ionospheric delay, and using the pseudo-random code on two frequencies. We find that the code receivers we use in this study are excellent references for comparing other ionospheric measurements. Receivers using the Klobuchar model exhibit some with correct values, others with problems. A receiver using a codeless technique appears to have problems. We also find that, because of potential uncertainties in calibrating code receivers, the IGS maps are particularly useful for time transfer.