Research On Ionospheric Delay Model Based On Dual-Frequency GNSS Signal

The fast development of Global Navigation Satellites System (GNSS) brings about many cross subjects, one of which in hot debate is GNSS Meteorology, a new subject appearing in recent years. In this field, GNSS satellites are used to achieve aerograph detection, including water vapor contents in the troposphere as well as the electrons density of the ionosphere. So GNSS Meteorology has been developed into a very important tool for weather forecast and climate monitoring. This advantage of GNSS satellites is due to that all the important parameters of atmosphere could be reflected from the transmission delay of the navigation signal. Also, just because of the impacts of the atmosphere on the transmission delay, the positioning accuracy will degrade. The key to solve this problem is to confirm the delay caused by the atmosphere. The more accurately the delay caused by atmosphere is detected, the more accurate the navigation position is and the more information about the atmosphere parameters can be got. Reversely, the deeper we understand the atmosphere structure, the more accurately the delay can be measured. Through such a progress, the navigation positioning technology and the atmosphere detection technology could both develop very fast. The main factor that causes the atmosphere delay, the ionosphere delay, is analyzed in this paper.First, based on the refraction theory as well as the ionosphere dispersion, the relationship of ionosphere delay along with the total electron density (TEC) and the navigation signal frequency is deduced. For convenience, here, the ionosphere single level model is adopted to represent the actual ionosphere structure. Then, the concept of vertical TEC (VTEC) and the function of projection can be used to calculate the relationship between VTEC and the dual-frequency GNSS signal. All this work serves as the theory pre-requisite of the ionosphere delay model based on the dual-frequency GNSS signal. And the experiment data is sampled by dual-frequency GPS receiver.Second, some traditional ionosphere delay models are compared. Through the analysis of the characteristics of these models as well as their application conditions, considering the object of this study, the VTEC polynomial function model is chosen to solve regional ionosphere detection for only one station.Finally, the VTEC polynomial expression model is set up according to the study of this paper and the experiment progress is introduced in details. Here, a dual-frequency GPS receiver is used to sample the actual data consecutively, and then, the data is further processed by computer. Based on the processed data, the VTEC can be calculated and the polynomial function model can be set up. By observing the delay of the zenith region of Kexueyuan of Harbin Institute of Technology, some law about the variation of VTEC in the daytime is summarized. The ionosphere delay model suitable to this region is set up. Some related analysis work including model accuracy and model usability is done.