  He-Ne ring laser gyroscopes are, at present, the most precise devices for
absolute angular velocity measurements. Limitations to their performance come
from the non--linear dynamics of the laser. Following the Lamb semi-classical
theory, we find a set of critical parameters affecting the time stability of
the system. We propose a method for estimating the long term drift of the laser
parameters and for filtering out the laser dynamics effects from the rotation
measurement. The parameter estimation procedure, based on the perturbative
solutions of the laser dynamics, allow us to apply Kalman Filter theory for the
estimation of the angular velocity. Results of a comprehensive Monte Carlo
simulation and results of a preliminary analysis on experimental data from the
ring laser prototype G-Pisa are shown and discussed.
