An Improved Ionospheric Correction Method for Wide-Area Augmentation Systems

A powerful approach for generating ionospheric corrections in wide area differential CJPS applications has been developed, that can bc applied to the Federal Aviation Administration’s Wide Area Arrgmcntation Systcm (WAAS). This approach has been used to support ionospbcric calibration for NASA’s Deep Space Network and will be supporting real-tirne operations for global ionospheric specification and, possibly, single-frequency satellite altimeter calibration. It is a real-time, grid-based technique relying on a cornputationally efficient Kalnlantype filter to produce accurate, smoothly varying ionospheric correction maps over the coverage area. Formal error maps are also computed, providing vertical delay errors over the WAAS grid, which are useful in integrity monitoring. This solution to the ionospheric correction problem is self-calibrating, since GPS transmitter inter-frequency biases are obtained as a byproduct of the mapping procedure. This contrasts with other techniques in which bias values must be provided from sornc additional source. Sinlulated data were gcncratcd for the proposed configuration of 24 WAAS reference GPS stations, using a well-tested clirnatological ionosphere model (Bent) to compute ionospheric total electron content (TEC) during conditions typical near the peak of the solar cycle, Slant TEC delays often exceed 30 meters over the continental US (CONUS) during solar maximum, but the simulations indicate that the corrections are accurate to 0.25-0.5 meter over the CONUS, Alaska and Hawaii (this inclrrdcs any errors in estimating the transmitter biases). Our technic]ue is therefore uscfrrl for en-route navigation and precision approach, the latter requiring 1.5 rnctcr correction accuracy.