## 1. Introduction

[2] Empirical electron density models, like the International Reference Ionosphere (IRI) [*Bilitza*, 2001] and NeQuick [*Radicella and Leitinger*, 2001] have been conceived to reproduce median values of the electron density in the ionosphere. In order to achieve better results in describing the three dimensional electron density of the ionosphere for actual conditions with NeQuick, a technique based on vertical total electron content (TEC) data ingestion into the model has already been developed [*Nava et al.*, 2005]. This technique relies on precalculated global vertical TEC maps to determine the corresponding global grids of the NeQuick driving parameter *Az*. Because of the preliminary computation needed to obtain the vertical TEC maps, the retrieval technique described in the work of *Nava et al.* [2005] cannot be considered a real-time procedure. For this reason a different approach based on NeQuick adaptation through direct slant TEC data ingestion has been adopted and two techniques to retrieve the electron concentration of the ionosphere have been developed using the model driven by its local ionization parameter *Az*. The first is a retrieval method that considers the slant TEC at a single ground station to determine the *Az*, and thus the electron density of the ionosphere, above the area surrounding the station. The second is a near-real-time retrieval technique able to reproduce the electron density of the ionosphere at a wider geographic scale being based on the calculation of regional grids of the NeQuick driving parameter *Az*. In this case, at any given epoch, the *Az* grid is computed from the slant TEC data obtained from a network of several ground stations. When an *Az* grid is computed, it is possible to reconstruct the three dimensional electron density of the ionosphere with the NeQuick model and therefore the TEC value for any given ray path above the area under investigation can be calculated by means of numerical integration.

[3] It must be noted that several ionosphere electron density reconstruction techniques have been developed. They are of different complexity and rely on several kinds of models. The Global Assimilative Ionospheric Model [*Wang et al.*, 2004], for example, is based on assimilation of data originating from different sources and implies the use of first principle models. The proposed retrieval methods aim to be simpler, being based on an empirical electron density model adaptation through the ingestion of TEC data only.