| For single-frequency users,ionospheric model is the main method to weaken the ionosphere delay.At present,the ionospheric correction models and broadcast parameters used in each navigation system vary,it is necessary to evaluate the correction effect of the model under the same benchmark.In order to evaluate the correctness of the model in a timely and accurate manner,it is necessary to select a reference with a high accuracy.The related literature points out that using CODE GRID products as a benchmark will have certain system deviations in some regions.In order to ensure the reliability of the assessment,this article selects the uniform high-precision reference value as the benchmark,using the actual measurement data of the station to extract the VTEC information at the puncture point of the station as a reference,and perform the evaluation and analysis of the ionospheric model correction effect.and the ionospheric delay correction model of each navigation system in 2017 was evaluated.During the evaluation process,it was found that the accuracy of modularity was affected by the abnormality of observed data and ionospheric magnetic storms.In this paper,the work of the observation data anomaly and ionospheric magnetic storm on the accuracy of the model is launched.The main content of this article is summarized as follows:1.This article first introduced several commonly used projection functions in the ionosphere,reference VTEC information extraction method,and elaborated user algorithms for GPSK8,BDSK8,BDSK14,BDSSH,and NeQuick2 five broadcast ionospheric models.2.For the URUM station,there is a jump in the DCB information at the receiver end in November 2017.This article expands the impact of change in DCB information on the performance of reference benchmarks and model performance.The results show that during the DCB mutation,there is a 10 TECU improvement in the extraction of reference information using the day-value information compared to the monthly average.To obtain a more accurate reference,use day-value information instead of monthly average information on the processing of satellite-and receiver-side DCB information.3.The VTEC information at the puncture point obtained from the day value information is used as a reference,this paper evaluates and analyzes the correction effects of the five broadcast ionospheric models in 2017.The results show that the performance of the BDSK14 model is better than that of the BDSK8 model in the comparison of the regional models.In the global model comparison,the BDSSH model is superior to the GPSK8 model and the NeQuick2 model in most regions.4.In view of the data quality abnormality of MTKA survey station on 139-141 days in 2017,this paper conducts a study on the impact of data quality anomaly on model performance evaluation.The results shows that: the impact of data quality anomaly on the model correction rate is more than 20%,and the effect on the root mean square errors RMS is 10-20 TECU,and the effect on the positioning accuracy is more than 5 m.5.In this paper,the small magnetic storm on April 4,2017 and the giant magnetic storm on September 8 were taken as examples to analyze the changes of ionospheric TEC perturbations during magnetic storms and the effect of magnetic storms on model corrections.This guides the ionospheric model in practical applications.The availability assessment provides a strong guarantee.The results show that the disturbance amplitude of small magnetic storms on ionospheric TEC ranges from 2 to 18 TECU in the disturbance of TEC,and the amplitude of disturbance of large ion storms to ionospheric TEC ranges from 10 to 40 TECU.For the effect of model correction,small magnetic storms have the greatest impact on GPSK8 model,NeQuick2 takes second place,and BDSSH model has the least impact.The degree of influence of the large magnetic storm on the model from low to high is BDSSH,NeQuick2,BDSK14,BDSK8,and GPSK8.It shows that the BDSSH model is slightly better than other models in terms of magnetic storm adaptability. |
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