Effects Of HOI Delay On GNSS Tropospheric Parameter Estimations

Global Navigation Satellite System（GNSS）signals are affected by ionospheric and tropospheric delays as they pass through the atmosphere,and the effects of ionospheric delay first-order terms can be eliminated through a linear combination of ionosphericfree conditions.However,the errors of the second-and third-order terms of ionospheric delay cannot be eliminated.With the need for high-precision GNSS applications such as precise point positioning and atmospheric parameter estimation,High-Order Ionospheric（HOI）delays can no longer be ignored.In view of the research and analysis of the effects of HOI delay on Multi-GNSS tropospheric parameters estimation,the main research contents and conclusions of this paper are as follows:（1）A software named RINGO has been developed and packaged using GO language to provide technical support for the correction of HOI delay in Multi-GNSS raw observation data.The correction is based on the latest 13th generation International Geomagnetic Reference Field（IGRF 13）model and Total Electron Content（TEC）of the ionosphere.This will enable the subsequent analysis of the effects of HOI delay on MultiGNSS tropospheric parameter estimation.（2）Regarding the effects of HOI delay on Multi-GNSS atmospheric parameter estimation,a study was conducted on randomly selected MGEX（Multi-GNSS EXperiment）stations in Australia from DOY（Day Of Year）16 to 29 in 2023,under normal solar activity.The experiment employed the RINGO software,which corrected for HOI delay using the latest 13th generation International Geomagnetic Reference Field（IGRF 13）model and Total Electron Content（TEC）of the ionosphere.Results showed that the maximum effects of HOI delay on Zenith Total Delay（ZTD）for BeiDou Navigation Satellite System（BDS）B1C/B3,Galileo Navigation Satellite System（Galileo）E1/E6,Global Navigation Satellite System（GLONASS）G1/G2,and Global Positioning System（GPS）L1/L2 were 4.60,3.00,3.10,and 3.10 mm,respectively.The North-South _gradient(NS_grad)was 8.4,5.90,4.90,and 6.12 mm,while the East-West _gradient(EW_grad)was 5.51,5.70,4.70,and 4.30 mm.The results further indicated that HOI delay has a greater effects on Multi-GNSS atmospheric parameter estimation in low signal frequency bands,low latitude regions,and during daylight hours when the solar activity is high.（3）Regarding the effects of HOI delay on the estimation of Multi-GNSS tropospheric parameters under different levels of solar activity.We conducted a study and analysis of MGEX stations in Australia for one week during high and low solar activity periods from DOY 9 to 15 and DOY 30 to 36,respectively.The experimental results indicate that the impact of HOI delay on the tropospheric ZTD and _gradients of Galileo E1/E6,GLONASS G1/G2,and GPS L1/L2 is greater during high solar activity periods than during low solar activity periods.However,the BDS B1C/B3 LARR and TOMP stations exhibit anomalies,which may be related to the loss of BDS B1C/B3 signal frequency bands at these stations.