Spatiotemporal variations in the ionosphere affects can be used for electron density or TEC computations. Global the HF and satellite communications and navigation systems. Positioning System (GPS) can be used to obtain TEC values Total Electron Content (TEC) is an important parameter since it with dual frequency receivers. With worldwide GPS satellites can be used to analyze the spatial and temporal variability of the and receivers TEC computations can be made continuously. ionosphere. In this

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... study, the performance of the two widely used Due to sparse measurements in space and time accurate and Kriging algorithms, namely Ordinary Kriging (OrK) and robust estimation techniques are needed to better investigate Universal Kriging (UnK), is compared over the synthetic data set. t v o In order to represent various ionospheric states, such as quiet and t riailt of the vionsphere. Inth study,Orinr disturbed days, spatially correlated residual synthetic TEC data Kriging (OrK) and Universal Kriging (UnK) algorithms, which with different variances is generated and added to trend are widely used methods in geostatistics are implemented on functions. Synthetic data sampled with various type of sampling synthetic TEC surfaces, using the method applied in [1], with patterns and for a wide range of sampling point numbers. It is additional factors. Synthetic TEC surfaces are generated for a observed that for small sampling numbers and with higher wide range of variance and correlation distances, with constant, variability, OrK gives smaller errors. As the sample number linear, second order polynomial, Gaussian surface, and a more increases, UnK errors decrease faster. For smaller variances in variable spatial trend surfaces. Synthetic TEC surfaces are the synthetic surfaces, UnK gives better results. For increasing varinceanddeceasig rngevales,usualy,theerrrs*sampled at a wide range of sample numbers and with various variance and decreasng range values, usually, the errors increase regular and random sampling patters. For the regular pattes, for both OrK and UnK. square, triangular and hexagonal grids examined in [2] are