At present,Precise Point Positioning(PPP)solution requires about 30 minutes or more to converge to an acceptable accuracy level.This is mainly due to the inadequate modeling of correlated GPS residual errors, including the higher-order ionospheric delay.In addition, neglecting these residual errors can lead to biases in the estimated orbit and clock solutions. rnIn this paper,we attempt to rigorously model the second- order ionospheric delay,which is the most significant among the higher-order ionospheric delay terms.The impact of second-order ionospheric delay on GPS satellite orbit and clock solutions is investigated.Implementation and handling of second-order ionospheric delay in PPP is also manipulated to achieve faster convergence time.
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