An observation model for earth tide displacements in application to Very Long Baseline Interferometry and similar precise geodetic techniques is developed. It incorporates effects from anelasticity, ellipsoidal figure, and fluid core resonance. Based on a harmonic development of the external potential, the model follows the familiar Love number concept. The transfer function of the earth to each harmonic is formulated in terms of coupled harmonics in the space domain and fulfils the causality condition in the time domain. Solve-for parameters can be chosen flexibly. The guideline, however, has been to provide a minimum set of well-defined and well-resolvable tide response parameters for analysis of observations. The aim of accuracy for tide displacements prediction is below 1 mm.
Being the major perturbation of the solid earth tide, ocean tide loading effects are computed, and the accuracy of the models involved is discussed. It appears that the major error source relates to those ocean tide frequencies for which global models are not available. These frequencies form a continuum with a power spectrum being largely a result of non-linear tide interaction. The associated loading effects cannot be reliably interpolated from global tide models, which are available only for a few distinct frequencies and which disregard tidal intermodulation. Thus, an accuracy of 1 mm for computed loading tide displacements cannot always be achieved.