In this paper, we present a four-dimensional (4-D) electron density model. The vertical distribution of the electron density is described by a F2-layer Chapman function combined with a plasmasphere layer function. The F2-layer peak density NmF2 and the peak height hmF2 are spatially and temporally modeled as 3-D series expansions in terms of localized B-spline functions depending on geographical longitude, latitude and time. The corresponding unknown series coefficients are estimated by a linearized model through an appropriate parameter estimation procedure. The input data are ground-based GPS data combined with electron density profiles retrieved from ionospheric GPS radio occultation measurements onboard the FORMOSAT-3/COSMIC, GRACE and CHAMP satellites, in order to compensate the insensitivity of the ground-based GPS data to the height parameter hmF2 as well as benefit from their different spatiotemporal resolutions. We verify our approach by measurements exemplarily over South and Central America for a selected time span during a solar minimum day 2008-07-01. Based on the B-spline method, we demonstrate an effective data compression by applying a multi-scale representation for the estimated coefficients derived from wavelet analysis.     «

In this paper, we present a four-dimensional (4-D) electron density model. The vertical distribution of the electron density is described by a F2-layer Chapman function combined with a plasmasphere layer function. The F2-layer peak density NmF2 and the peak height hmF2 are spatially and temporally modeled as 3-D series expansions in terms of localized B-spline functions depending on geographical longitude, latitude and time. The corresponding unknown series coefficients are estimated by a linear...     »