Research on Klobuchar Improved Model Based on the Measured Data of BeiDou Satellite Navigation System in Tianjin Area

Abstract

The Klobuchar model, which is mainly studied in this paper, can be used to correct ionospheric delay errors for single frequency receivers. What’s more, the Klobuchar model is an empirical model based on long-term observations and can decrease the ionospheric delay error by 50% to 60% in the mid-latitudes. However, the Klobuchar model is applied to global scope and its accuracy is limited by the update frequency of model parameters. So Klobuchar model correction accuracy and validity are decreased if this model is only used in a specific region. Because of the limitations of the Klobuchar model in application, there have been 14-parameters Klobuchar model[1], 13- parameters Klobuchar model[2] and 10-parameters Klobuchar model[3] for further correcting ionospheric delay errors in different countries and regions. Based on the study of these models, this paper proposes the algorithm different from these models by combining the relax iterative with the linear search, and presents a Klobuchar improved model for Tianjin area that is designed to improve the precision of ionospheric delay error correction. The navigation data in this paper are obtained from the Novatel GPStation-6 receiver (GNSS Ionospheric Scintillation and TEC Monitor Receiver) and the global ionospheric grid data are published by IGS (International GNSS Service). The measured data of eight weeks were randomly selected from the data collected (December 2016 to July 2017). After using the data to calculate and analyze the original Klobuchar model, five parameters were added to the model in addition to the eight correction parameters broadcasted by navigation message. And then the values of these additional parameters are obtained through the algorithm combining relax iterative and linear search. The correction accuracy comparison is made between the new model and the original model, which is based on the ionospheric delay data released by IGS and the ionospheric delay data obtained from the Beidou satellite navigation system dual frequency observations. The results show that about 10% of the average correction accuracy of the ionospheric delay in Tianjin is improved without considering the inherent small bias of the receiver.