Ionospheric Modelling in the North of Algeria

The knowledge of the ionospheric behaviour is an important factor in GPS positioning. Data of five ALGEONET (Algerian GEOdynamical NETwork) and a hundred IGS stations are processed with the Bernese GPS software, which is based on the use of spherical harmonic expansion, to provide an ionospheric mapping of the Total Electronic Content (TEC). The used model supposes that the whole free electrons are concentrated on a thin spherical layer to an altitude varying between 250 and 450 km. Results are obtained for several heights (350, 400 and 450 km) with a 2-hourly resolution. The maximal value of the obtained TEC in the north Algerian area is about 20 (midnight) to 60 (midday) TECU, such values are obtained for the day of April 30, 2001, which refers to a high solar activity period with a sunspot number of 112. Calculated TEC values are thereafter applied to correct the single frequency solution. The comparison between the corrected $L1$ and ionosphere-free solutions shows that the ionospheric effects involve a network contraction. Also, the corrected $L1$ solution is close to the ionosphere-free one; for baselines of several hundreds of kilometers, deviations are about 10 cm (in horizontal coordinates), they are reduced by about 50% in vertical component