What is the effect of user and CORS height on NRTK performance?

Network Real Time Kinematic (NRTK) positioning is nowadays a very common practice in many parts of the world. The benefits of NRTK positioning and the details of network products have been previously discussed in this column (see the contribution by Leila Kislig in the July/August 2011 issue of Inside GNSS), as has the positioning performance as function of the inter-station distances of the network’s continuously operating reference stations (CORS) (see the contributions by P. Dabove et alia in the November/December 2011 issue). However, because GNSS measurement errors are modelled by the network software, the quality of the differential corrections sent to the rover depends on the ability of the network to estimate errors (mainly the atmospheric ones) at individual stations, as well as the capability to spatially model the errors. So, what are the CORSs requirements in order to have good NRTK positioning, considering a multi-frequency and multi-constellation receiver, even in areas with extreme changes in altitude? More specifically, can a heterogeneous network in terms of height of CORS sites be used to obtain centimeter-level accuracy for the rover? We carried out some experiments to answer these questions and present the results in this article.