Ionospheric delay estimation of Loran skywave using simple cosine model

Ionospheric delay is the most significant source of error affecting the Loran skywave timing. To improve timing service, we propose a new ionospheric delay estimation method in this paper. It is a cosine model that combines the ionospheric physical characteristics and skywave delay variation law. This semi-empirical and semi-measured model has characteristics of accuracy and simplicity compared with the traditional method. The experimental results show that estimation error of the model is less than 1 mu s for a single day and less than 2 mu s for 3 days in the stable time. It is sufficient to correct more than 90% of delay when skywave passes through the ionosphere and is less affected by the season. This paper also gives some suggestions on the propagation of ionospheric coefficients required for the model. It allows broadcasting only by modifying the data channel message structure under the normal operation of Loran system.