GPS and Ionosonde Data Fusion for Ionospheric Tomography

GPS measurements are combined with ionosonde measurements in an estimation problem for the state of the quiescent local ionosphere. This estimator has been developed to remotely sense the ionosphere above the High Frequency Active Auroral Research Program (HAARP) heater facility in Gakona, AK. The measurement model used by the estimator consists of a refractive ray-tracing model of ionosonde measurements for the electron density profile and of dual-frequency GPS measurements. A set of parameter sensitivity calculations augment the ray-tracing solutions in order to facilitate standard estimation-based model inversion calculations. The resulting algorithm determines an optimal parameterization of the ionosphere’s electron density profile. Ionosonde data provide information about bottomside ionospheric layers, and trans-ionospheric GPS signal data enable observability of topside structure and a simple characterization of its variations with respect to latitude and longitude through implicit correlation of slant total electron content (TEC) integrals with the bottom side characterization. Experimental ionosonde and GPS data have been recorded and used to fit the ionosphere models. The result are ionosonde virtual height measurement fits within 8 km, and frequency-differenced GPS pseudorange fits within 0.2 TEC units.