The majority of navigation satellite receivers operate on a single frequency and
experience an error due to the ionospheric delay. They compensate for the ionospheric
delay using an ionospheric model which typically only corrects for 50% of
the delay. An alternative approach is to map the ionosphere with a network of
real-time measurements, with either a thin shell approximation or a full 3D map.
Here, a time-dependent 3D tomographic imaging technique is used to map the free
electron density over the full-height of the ionosphere during solar maximum. The
navigation solutions computed using corrections based upon models and thin-shell
and full-height maps are compared in this project.
The models and maps are used to calculate the excess propagation delay on the L1 frequency experienced by GPS receivers at selected locations across Europe
and North America. The excess delay is applied to correct the pseudo-range single frequency observations at each location and the improvements to the resulting positioning
are calculated. It is shown that the thin-shell and full-height maps perform almost as well as a dual-frequency carrier-smoothed benchmark and for most receivers
better than the unfiltered dual-frequency benchmark. It is also shown that the unfiltered dual-frequency method is not reliable, which is of concern as it is a
proposed upgrade to current positioning systems. The improvements in positioning accuracy vary from day to day depending on ionospheric conditions but can be up
to 25m during mid-day at solar maximum conditions at European mid-latitudes.
The full-height corrections perform well under all geomagnetic conditions and are
considerably better than thin-shell corrections under extreme storm conditions.
The transmission of the navigation correction requires a forecast, an image compression
and a system of distribution across a local region. The feasibility of this is
demonstrated for regions of land and near-land coastal regions across Europe.
|Date of Award||1 Jul 2009|
|Sponsors||Engineering and Physical Sciences Research Council|
|Supervisor||Cathryn Mitchell (Supervisor)|