Research On Ionosphere Delay Correction Method For Real-Time Point Positioning

Single point positioning is a commonly used technology in GNSS,and ionospheric delay is one of the most important sources of error in single point positioning.The accuracy of the ionospheric delay correction model directly affects the accuracy of single frequency point positioning and the convergence of single frequency precise point positioning.The dual-frequency ionosphere free combination can make noise and other errors amplificated.This paper analyzes the applicability of different ionospheric models in single frequency point positioning.The prediction method and application of GIMs grid model is also studied in this paper.At the same time,the ionosphere-weak combination model with the advantage of noise reduction is proposed,and the ionosphere weak combination positioning effect is verified and evaluated with the data of BDS/GPS in different observation environment and state.The main contents and conclusions of this paper are as follows:1.Comparing the single-frequency SPP results of GIMs products from different analysis centers,it is proved that the single frequency SPP accuracy under the GIMs product is generally higher than the double frequency SPP result.It is found that there is regional anomaly in GIMs data,which results in the accuracy of single frequency SPP is lower than dual frequency SPP.According to the positioning result of PPP.CODE GIMs products is proved to be stable enough as the benchmark value for broadcast ionospheric model in the suitable area.2.The inapplicability of the BDS/GPS Klobuchar model in the spatio-temporal domain is theoretically analyzed and experimentally verified.It is pointed out that there is a great deviation between the night constant value model of Klobuchar and the grid model in the peak of the solar activity peak.By calculating the parameters,it is found that the amplitude of the Klobuchar model will appear negative phase anomaly in the high latitudes,and it contradicts the model hypothesis.3.The ionosphere model BDGIM of Beidou3 global satellite navigation system is studied in this paper.The VTEC sequence is calculated according to the 9 spherical harmonic parameters fitted by the measured data.The result is consistent with the low order spherical harmonic coefficient published by CODE,and the superior of the BDGIM model compared to the BDS/GPS Klobuchar model is verified.The broadcast parameter is used to calculate the VTEC sequence,too.It is found that there is a large gap between the GIMs grid in the partial latitude area.It is considered that the test satellite has a certain truncation error in the process of transmitting the ionospheric parameters to the user,which results in a large deviation between the ionospheric VTEC and GIMs reference values calculated from the broadcast parameters in the partial latitude regions.4.The theory and prediction method of ARIMA model are studied in this paper.The model is used to forecast the long sequence of GIMs data.The prediction accuracy under different prediction steps in 2006-2015 years is calculated.It is found that the prediction error will increase with the increase of the prediction step,and in different solar activity period,the difference of prediction accuracy is great.No matter in which ionosphere active period,the precision of GIMs forecast product can be guaranteed to be superior to Klobuchar model.In addition,the ionospheric prediction value is selected as the reference background value to improve the traditional anomaly detection method,and to detect and mark the anomalous area of the ionospheric grid data.Compared with the traditional anomaly detection method,the improved method has a higher accuracy rate for GIMs data anomaly detection.5.In view of the problem that dual frequency ionosphere free combination can amplify the noise,a ionosphere weak combination model that can take account of both noise and ionospheric delay correction is proposed in this paper.Combined with the measured data of BDS/GPS,traversing the SPP positioning experiments under different combinations,it is confirmed that the GPS system has the best code ionosphere weak combination.In BDS system,due to the factors such as the multi-path of the satellite end and the TGD parameter correction in the broadcast ephemeris,the code pseudo distance ionosphere weak combination can not improve the three-dimensional positioning accuracy of the BDS SPP.In the static PPP positioning experiment,it is proved that in the GPS system,the combination of the code and the carrier phase ionosphere weak combination can bring the convergence speed and the convergence precision up simultaneously.In the BDS system,the carrier phase ionosphere weak combination can significantly improve the positioning accuracy after convergence.Combined with the real-time data onboard the sea,the dynamic point positioning experiment has verified that GPS ionosphere weak combination PPP has significantly improved both in dynamic positioning accuracy and convergence time.Limited by the observation period length,weak ionospheric combination The effect of improving the positioning of BDS dynamic PPP is not obvious.