Accurate ionospheric error correction for differential GPS

In differential GPS the ionosphere induced error in range is determined at a reference station (of known location) and then relayed to another (mobile) station whose accurate position is to be determined. For the method to work effectively the mobile station should be within about 10 km of the reference station although a network of reference stations can be used to provide corrections over a given area. In this paper we present modelling calculations to determine differences in ionosphere induced delay between nearby reference and mobile stations to an accuracy of a millimetre. This is so that empirical formulae can be formulated to accurately determine the difference in ionospheric delay expected over a short baseline to enable a more accurate differential GPS correction to be made.