Ionosphere Integrity Monitoring Of Network RTK

Integrity is the ability which the system sending out warning signals to users when navigation system has any failure or error exceeding can't be applied for navigation and positioning service.This topic examines quality and integrity issues that need to be managed in order to successfully operate a real time network.The ionosphere delay is the principal error affecting the positioning in the network RTK,its changes are very complicate and the most difficult to model.A large part of ionospheric error can be modeled and removed by using NRTK system.However,during storms or ionospheric disturbances,a large ionospheric residual remain,and that affect on the determination of the phase ambiguities and the performance of the network RTK.Therefore,the integrity monitoring is in fact necessary to control the ionospheric residual error,in order to guarantee the reliability and availability of the rover positioning.The ionosphere integrity monitoring of Network RTK includes the following four aspects.Firstly,estimation and analysis of ionosphere delay;secondly,construction of ionosphere interpolation model;thirdly,calculation of ionosphere residual integrity monitoring(IRIM);fourthly,calculation of the ionosphere residual interpolation uncertainty(IRIU).Two sub-networks data from Guangdong province in China for the day of September 11th,2015 and September 22nd,2015 with sampling interval one(01)second are used in our experiments.Baseline length plays an essential role in the ability to resolve ambiguities to their correct integers.The shorter the baseline length is,the smaller the remaining error gets.The double-differenced ionosphere delay value is in decimeter level,it becomes larger when the length of the baseline is longer.So,the ionosphere delay value depends on the length of base line.Due to the characteristics of the ionosphere activity and its dispersive state in the space,it is ubiquitous to use regional error models to predict correction values for the rover.Among these models,the linear interpolation method(LIM)is typical and most used for establishment interpolation model for obtaining the predicted error values for the rover's location,which was proposed by Wanninger(1995).The analysis of the ionospheric correction residuals performed for different periods and networks indicated varied accuracy of the corrections and its dependency on the ionospheric conditions.True DD ionospheric delay and DD ionospheric residual are affected by sun radiation and when the ionosphere is more severe especially in the period of afternoon and the evening.The ionospheric activity variation depends on the quantity of sun radiation.As the linear part of ionospheric residual is generally taken out by the interpolation methods,the nonlinear part,which is not modeled by the interpolation,remain in the network.Thus,the ionospheric linearity could provide good estimation of the ionosphere interpolation error and ionosphere residual error within the network.After calculating the double difference ionosphere delay of baseline and establishing the interpolation model,Ionospheric Residual Integrity Monitoring(IRIM)and Ionospheric Residual Integrity Uncertainty(IRIU)are used to monitoring these remaining residuals.The corresponding values of both integrity monitoring indicator IRIM and IRIU are the similar to the change of ionospheric residual.IRIM and IRIU both reflect the situation of ionosphere residuals.