Research On Regional Ionosphere Modeling Based On GNS

The ionospheric effect seriously affected the GNSS navigation,positioning,and time service,and was one of the important error sources in the GNSS calculation process.Establishing an ionospheric model through GNSS observation data was currently the main technical means for conducting ionospheric research.The dense CORS service system base stations provided rich and reliable data sources for regional ionospheric modeling.Building a regional ionospheric model based on CORS observation data could accurately reflect the ionospheric activity and changes in the region.China has a vast territory and spans a wide range of latitude and longitude.There were different forms of ionospheric changes in different regions,and the level of ionospheric activity varied in different periods of the same region.How to select appropriate models and orders to accurately fit the regional ionosphere in the face of different ionospheric distributions was a key issue worth studying in regional ionospheric modeling.At the same time,the ionospheric activity in low latitude areas was extremely intense due to the influence of the "equatorial anomaly",and traditional single-layer modeling methods had insufficient modeling accuracy,making it impossible to accurately fit the active ionospheric changes.Affected by the intensification of solar activity,geomagnetic explosions occurred frequently.Studying the abnormal response of the ionosphere during magnetic storms was of great significance for clarifying the mechanism of ionospheric changes and improving the accuracy of ionospheric correction under abnormal conditions.In response to the above issues,this article used regional CORS network observation data to finely construct and improved regional ionospheric models,and studied the spatiotemporal response characteristics of ionospheric anomalies caused by geomagnetic storms.The relevant research results were as follows:(1)We have designed an evaluation scheme for the results of ionospheric delay extraction,and evaluated the accuracy of phase smoothing pseudorange method and non difference non combination PPP method in extracting ionospheric delay.Analyzed the advantages and disadvantages of phase smoothing pseudorange method and non differential non combination PPP method for extracting ionospheric delay,and designed a scheme for evaluating the accuracy of ionospheric delay extraction with zero/short baseline inter station differential evaluation.Two methods were used to extract ionospheric delay for inter station differentiation,and the inter station single difference of 6 sets of zero/short baseline ionospheric delay extraction values was compared.Compared to the phase smoothing pseudorange method,the inter station single difference mean square error of extracting ionospheric delay using non differenced and non combined PPP reduced by 69.7%-86.1%.PPP results are more stable and extraction accuracy was higher.(2)The optimal order for constructing a regional ionospheric model using spherical harmonic functions was provided.It was recommended to use a secondorder spherical harmonic model for regional ionospheric modeling.The ionospheric modeling results of various orders of spherical harmonic functions under different active states indicated that during the calm period of the ionosphere,the modeling effect of the 1-5th order spherical harmonic model VTEC was equivalent,with a mean deviation from the CODE product VTEC of 2.286 TECU-3.300 TECU.During the active and abnormal periods of the ionosphere,the second-order model VTEC had the highest modeling accuracy,with the mean VTEC deviation of 4.121 TECU and 4.546 TECU,respectively.As the order of the spherical harmonic model increases,there was no significant improvement in the ionospheric fitting accuracy of spherical harmonic models above order 2.The results of ionospheric modeling in different latitude zones indicate that the modeling accuracy of second-order spherical harmonic models in different latitude zones was the best.The mean VTEC deviation of second-order models in a certain province in Northeast,North China,and Southwest is 0.261 TECU,0.613 TECU,and 0.764 TECU,respectively.As latitude decreased,the regional ionosphere gradually became active,the fitting accuracy decreases,and the error in fitting residuals gradually increased.(3)A hybrid multi-layer ionospheric model has been proposed to improve the accuracy of regional ionospheric modeling.The existing multi-layer ionospheric modeling methods mainly focused on the distribution of electrons in the middle and upper layers of the ionosphere,without considering the concentration of electron content in low latitude regions during active periods at lower altitudes,which limited the accuracy of ionospheric active period modeling.Based on the ionospheric altimeter data,this paper analyzed the relationship between the electron density and the peak height during the period of high solar activity level.A hybrid multi-layer ionospheric model was proposed,using a three-layer model with a height of 150 km,300km,and 450 km during the active and active recovery periods of the ionosphere from 13 to 21 local time,and a single-layer model with a height of 450 km during the rest of the ionospheric calm period.Compared with traditional single-layer models,the new model has significantly improved modeling accuracy,with an increase of6.42%-52.08% in external coincidence accuracy and 37.37%-59.12% in internal coincidence accuracy.(4)Studied the spatiotemporal response characteristics of ionospheric anomalies caused by geomagnetic storms on the Earth.A regional ionospheric model was constructed before and after the occurrence of a magnetic storm,and ionospheric anomalies were extracted.The response characteristics of ionospheric anomalies during the magnetic storm were obtained: geomagnetic storms can cause ionospheric anomalies,which have a trailing effect in response time.It took 24 hours after the end of the magnetic storm for the ionosphere to recover to its normal level before the storm.A small magnetic storm caused an increase of approximately 9.5TECU in the total number of electrons in the ionospheric zenith direction,corresponding to an increase of approximately 36 TECU in the line of sight direction.The ionospheric anomaly response in high latitude regions was greater than that in low latitude regions.During the magnetic storm,the ionospheric anomaly response first showed an increasing and extending trend from south to north.When the ionospheric VTEC and its outlier reached the peak,the ionospheric anomaly response showed a regression trend of weakening from north to south.