A new approach for mitigating ionospheric mapping function errors

Kurzfassung

Space-based navigation systems operating at single frequencies below 10 GHz require ionospheric information for correcting the signal delay or range error. In order to mitigate ionospheric errors as well as satellite clock and orbit errors especially in aircraft navigation, Space-Based Augmentation Systems (SBAS) such as WAAS and EGNOS have been established worldwide. In the current standard, the SBAS broadcasts vertical ionospheric delays at the ionospheric grid points (IGP) spaced by five degrees in latitude and longitude. The vertical delay is converted at user level to the required specific slant delay by using an obliquity factor called mapping function (MF) derived under the simplifying assumption of a thin-shell ionosphere fixed at 350 km height. In the present work we compared the performance of the thin-shell MF with a new MF approach derived based on multi-layer ionosphere assumption using data from a network of about 200 ground GNSS stations worldwide. We have found that using the new MF instead of the thin-shell MF the mean errors in slant delay computation can be reduced by more than 50% regardless of the user location and ionospheric conditions.