Estimation of EOP from VLBI: Direct Approach

The currently adopted strategy of EOP estimation from VLBI is to estimate six parameters: UT1, UT1 rate, pole positions and nutation o sets for each 24-hour session independently. Then the resulting time series of raw Earth orientation parameters are ltered and a regression analysis is performed in order to obtain nutation coe cients, polhode of the pole and other physical parameters. Thus, the latter parameters are obtained indirectly in two stages. An alternative approach of direct estimation of the nal Earth orientation parameters is presented. Pole coordinates and UT1 are considered as a sum of three components: the low-period component which is modeled by a cubic spline, the harmonic component which includes forced nutation, precession and subdaily variations of EOP, and the stochastic component which is modeled by a linear spline with segment length 1{2 hours. All parameters are obtained in a single LSQ solution using all available data.