In this paper, a subspace fitting method is proposed to update, in the time domain, the
finite element model of a rotating machine. The procedure is achieved by minimizing an
error norm, leading to the comparison between experimental and theoretical observability
matrices. Experimental observability matrix is obtained through a MOESP subspace
identification algorithm, by projecting the output signal onto some appropriate subspaces,
resulting in a cancellation of input excitations and noises. The theoretical observability
matrix is obtained from modal parameters of a finite element model of the structure. The
minimization procedure is carried out through a Gauss-Newton algorithm. The method is
applied to determine the foundation stiffness of an experimental rotating machine subject
to a random noise.