Spatial Layout Optimization Method Of Multi-frequency Multi-mode CORS

The core of Network RTK technology is to use the ionospheric interpolation model formed by the ground-based continuous operation reference station(CORS)network for enhancement.Therefore,the design of CORS spacing is directly related to the accuracy of regional ionospheric model.The average distance of CORS system based on dual frequency observation is usually less than 80 km,which can ensure the interpolation accuracy of ionospheric model,but the shorter distance of CORS station undoubtedly increases the construction cost.With the rapid development of major satellite systems,the triple frequency signal of each system can increase the observation,better constrain the double difference ionospheric delay,greatly improve the multi frequency CORS spacing,and form a sparse network.This paper summarizes the previous research results,analyzes the temporal and spatial variation characteristics of the double difference ionospheric delay,and focuses on the accuracy of the double difference ionospheric interpolation model in CORS network with different reference station spacing in different regions,and designs relative positioning simulation experiments to analyze the CORS system spacing from the result of ambiguity resolution,The maximum design upper limit of CORS station spacing in each area is discussed.The main research results are as follows:1.The results show that the double difference ionospheric delay increases proportionally with the increase of the baseline length;The correlation between the F10.7 index and the double difference ionospheric delay is stronger,so it is more reasonable to use the F10.7 index as the data of solar activity;The double difference ionospheric delay in low latitudes is obviously larger than that in middle and high latitudes.2.Taking Lim model as the main research object,the accuracy of CORS network ionospheric interpolation model with different reference station spacing under different latitude distribution is analyzed.The results show that when the latitude is greater than 22°N,the distance between reference stations and the intensity of solar activity are important factors affecting the interpolation accuracy.Moreover,with the increase of the distance between reference stations,the influence of solar activity on the interpolation accuracy is greater.In the low latitude region of 19°?22°N,the interpolation accuracy of the observation network with the same reference station spacing is significantly weaker than that in the middle and high latitudes,and the accuracy of the observation network with 35 km spacing in the low latitudes is the same as that of the observation network with 70 km spacing in the middle and high latitudes.3.According to the above results,the corresponding simulation experiments are designed to verify whether the ambiguity can be effectively fixed under the corresponding double difference ionospheric delay constraint,so as to achieve the goal of CORS layout optimization.The results show that the effect of ambiguity resolution is significantly improved by comparing the three frequency observation with the two frequency observation;The double frequency observations should ensure 100% ambiguity resolution success rate in 20 epochs,and the ionospheric interpolation accuracy is less than 0.05 m.The triple frequency observations should ensure 100% ambiguity resolution success rate in 20 epochs,and the ionospheric interpolation accuracy is less than 0.06m;According to the accuracy requirements of the above interpolation model,when the latitude is greater than 28°N,the distance between reference stations of CORS system based on dual frequency observation should reach 70 km,and the distance between reference stations of CORS system based on triple frequency observation should be less than 84km;At 19°?22°N area,the distance between reference stations of CORS system based on dual frequency observation needs to be controlled within35 km,while the distance between reference stations of CORS system based on triple frequency observation needs to be less than 42 km.