Influence of Higher-order Ionospheric Delay Correction on Static Precise Point Positioning

We modified the un-differenced precise point positioning(PPP) mathematical model considering the second-and third-order ionospheric correction.The influence of the higher-order ionospheric corrections on both GNSS observations and static PPP are analyzed with respect to aspects of site location and ionospheric environment by using a globally distributed network which is composed of 38 IGS tracking stations.Numerical experimental results show that,higher-order ionospheric influences on the observation as well as static PPP at low-latitude regions are more significant than that of mid-and high-latitude regions.For static PPP,the influence in low-latitude regions(<30°) reaches about 3-5mm,and is only a sub-millimeter in other regions(>30°).Furthermore,the impact is mainly visible in the direction of North and South direction,showing a southward migration trend,especially at the lower latitudes where the influence value is likely to be more than 3 mm,2 to 3 times that of the East and Up components.The level of ionospheric activity may also have impact on positioning results,and the influence during active periods is about 20-30% higher than that of quiet periodd.