The results of the determined ionization identifier TEC (Total Electron Content) for continuously operating reference Global Navigation Satellite Systems (GNSS) stations are analysed. On the one hand, the data reflect the state of the ionosphere during the observation; on the other hand, it is a substantial tool for accuracy improvement and reliable determination of coordinates of the observation place. It was decided to solve a problem of restoring the spatial position of the ionospheric state or its ionization field according to the regular definitions of the TEC identifier, i.e. VTEC (Vertical TEC). We have described one possible way of solving this problem, which is based on mathematical modelling by using degree polynomials and trigonometric Fourier series. Degree polynomials describe the trend of function, whereas the trigonometric Fourier series are used in order to better simulate the fluctuation. The method was tested for network of permanent stations ZAKPOS.

The role of space geodetic techniques combination is becoming increasingly important to calculate the geodetic parameters. It has an intention of using the advantages and complementarity of different techniques to achieve the best solution. Estimation of geodetic parameters from observations mainly was done by least squares adjustment within the Gauss - Markov model. The combination can be done at three different levels: observations, normal equations and parameters. This article analyses the differences between the approaches and discusses the possibility of troposphere parameters calculation from a theoretical point of view.