Research On Elaboration And Application Of GNSS Ionospheric VTEC Modeling

The development of ionospheric VTEC modeling and GNSS is a mutually reinforcing process.With the rapid development of GNSS systems,the establishment of a high-precision ionospheric VTEC model based on GNSS technology has become the main technical means at present.This paper has studied and discussed the data preprocessing,optimization of model coefficients,quality analysis of modeling results,generation of regional models,and detection of ionospheric anomalies before earthquakes in the establishment and application of VTEC models.The main contents include:1.Based on the P4 observation equation,by analyzing the statistical results of long-term VTEC products of IGS,partial ionospheric modeling results,and general assumptions,the limits of P4 observations were studied and formulated,and the different ionospheric active periods of IGS stations at six different latitudes were studied.The P4 observations were grossly inspected to show the applicability and rationality of the given tolerances,which provided a reliable data base for the establishment of ionospheric VTEC models based on P4 observations.2.Aiming at the shortcomings of the traditional TurboEdit algorithm in detecting small cycle slips in the initial epoch,a two-way TurboEdit algorithm based on the BIC criterion is proposed.The experimental results show that the improved algorithm is stable in detecting and repairing the fixed cycle slip and the random cycle skipping combination.There is a clear improvement;based on the analysis of the relationship between the weekly jump fixed success rate and the standard deviation of the cycle jump detection,the pseudo-range view measurement will introduce a relatively large error defect,and a three-frequency observation data based on the Beidou is proposed.A three-step method for detecting and repairing cycle slips was performed.The experimental results show that the three-step method can accurately detect and repair all the simulated cycle slips added,and can realize real-time cycle hopping detection and repair.The completion of the cycle jump detection and repair scheme laid the foundation for the establishment of an ionospheric VTEC model based on L4 observations and further based on tri-band observation data.3.An in-depth re-study of the moving optimized polynomial method was carried out,including the application of different optimization criteria in the establishment of the ionospheric VTEC model,the generation of complete day modeling results,and the quality analysis of continuous multi-day modeling results under different conditions.The research shows that the model of the least error criterion in the unit weight of post-examination has the advantages of high accuracy and good continuity;the least error modeling method in the unit of sliding post-test weight has excellent accuracy in different periods and at different latitudes.Characteristics,in the high and low years of solar activity,can obtain modeling results with better accuracy than 2TECU and 1TECU respectively.If only mid-latitude stations are considered,the modeling results with better accuracy than 0.8TECU can be obtained.Compared with IGS grid products,in the low solar activity years,the average precision increased by 65% and 35% at low and middle latitudes respectively,and maintained a considerable level at high latitudes;In the high solar activity years,the average precision increased by 70%,79% and 35% at low,mid-and high-latitudes respectively.4.A mosaic method for generating a regional ionosphere model based on single-station modeling results is presented,and an ionospheric VTEC model for China region is generated based on P4 observations and L4 observations,respectively.The analysis of the two modeling results shows that the two show obvious consistency,and the accuracy of L4 modeling is significantly higher than that of P4.The two parts with poor accuracy appear at the edge of the single station monitoring area.Comparing the modeling results with the IGS grid,the results show that the regional modelling results have higher accuracy and can better describe the details of the local changes in the ionosphere.All of them show strong consistency in both VTEC values and distributions.Sex,verified the reliability of the modeling results in this article.5.The VTEC anomaly detection method using pre-seismic VTEC data and IGS grid VTEC data were respectively used for experimental analysis,pointing out the deficiencies of the traditional methods.At the same time,a grey prediction model method was proposed.Experiments show that the grey prediction model method can obtain more High-precision background reference values and more reasonable error limits have certain advantages.