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.