Magnitudes and temporal variations of the tropospheric and Ionospheric errors in GPSnet

One of the main factors that lead to better performance of a Network RTK (NRTK) system is to predict/generate and transmit high accuracy error corrections from the central server for the rover's location without much latency. The corrections are mainly for the atmospheric errors i.e. the tropospheric and ionospheric errors. These two types of atmospheric errors can be calculated and transmitted either separately or together, depending on the way the NRTK system is implemented. It is commonly thought that the magnitudes and temporal variations of the two types of atmospheric errors are quite different. For example, it is often emphasized that the ionospheric errors vary more quickly with time and so more difficult to be modeled than the tropospheric errors. In this paper, comparisons of the differences in the magnitudes and temporal variations between the double differenced (DD) tropospheric and ionospheric errors were conducted using GPS observations from GPSnet, the Victorian CORS network. Test results indicated that both types of the DD atmospheric errors significantly contaminate GPS measurements regardless whether it was day time or nighttime. Test results also showed that the temporal variation amplitudes of the DD tropospheric residuals in a fixed time span was not always significantly less than that of ionospheric residuals. In some cases, the DD tropospheric residuals reached several centimetres in a one-minute time span. These results can be instructive in the determination of the way a NRTK system is implemented, e.g. the rates or frequencies for generating and transmitting both types of atmospheric corrections.