Results in terms of residuals for an estimation of initial state and once-per-orbit libration amplitude and an estimation of initial state and gravity coefficients. The observations are generated with a coupled model and estimation is performed with an uncoupled model. Panel a: component-wise post-fit residual history of an estimation of initial state and libration amplitude. Panel b: frequency content of the S components of residuals for all three different estimations: initial state, initial state and libration amplitude, initial state and gravity coefficients. Vertical lines indicate (integer multiples/divisors of) the mean motion (solid) and the three normal modes: longitudinal (dotted), latitudinal (dashed) and wobble (dash-dot-dot).