Proposed Methods of Estimating Ionospheric Delays from GPS Data for Precise Point Positioning

摘要

After the elimination of Selective Availability (SA), ionospheric delay effects are next largest error sources in GPS positioning and navigation. Performance of point positioning from GPS code phase (pseudorange) data depends primarily on how accurately ionospheric delay can be corrected. For this purpose, single frequency GPS users are assumed to apply the broadcast model (Klobuchar model) with the use of ionospheric parameters broadcast in the GPS navigation message, but it typically corrects for 50 percent of the ionospheric delay. On the other hand, dual frequency GPS users can correct using dual frequency code phase data. However, this is not the obvious process, since GPS data contain differential instrumental biases of the GPS satellites and the receiver as well as multipath and random errors. Several papers have considered this problem of estimating ionospheric group delays and biases using either least squares or sequential estimation approach. In this paper we have proposed sequential methods for estimating both group delays and biases from two frequency GPS data using both code and carrier phase data, and demonstrated its effectiveness in ionospheric group delay estimation.