Methods and systems for estimating values of parameters of interest from optical measurements of a sample early in a production flow based on a multidimensional optical dispersion (MDOD) model are presented herein. An MDOD model describes optical dispersion of materials comprising a structure under measurement in terms of parameters external to a base optical dispersion model. In some examples, a power law model describes the physical relationship between the external parameters and a parameter of the base optical dispersion model. In some embodiments, one or more external parameters are treated as unknown values that are resolved based on spectral measurement data. In some embodiments, one or more external parameters are treated as known values, and values of base optical dispersion model parameters, one or more external parameters having unknown values, or both, are resolved based on spectral measurement data and the known values of the one or more external parameters.