  It is customary to perform analysis of the Earth's rotation in two steps:
first, to present results of estimation of the Earth orientation parameters in
the form of time series based on a simplified model of variations of the
Earth's rotation for a short period of time, and then to process this time
series of adjustments by applying smoothing, re-sampling and other numerical
algorithms. Although this approach saves computational time, it suffers from
self-inconsistency: total Earth orientation parameters depend on a subjective
choice of the apriori Earth orientation model, cross-correlations between
points of time series are lost, and results of an operational analysis per se
have a limited use for end users. An alternative approach of direct estimation
of the coefficients of expansion of Euler angle perturbations into basis
functions is developed. These coefficients describe the Earth's rotation over
entire period of observations and are evaluated simultaneously with station
positions, source coordinates and other parameters in a single LSQ solution. In
the framework of this approach considerably larger errors in apriori EOP model
are tolerated. This approach gives a significant conceptual simplification of
representation of the Earth's rotation.
