Metrology method and apparatus, computer program and lithographic system

Disclosed are a method, computer program and associated apparatuses for metrology. The method includes determining a reconstruction recipe describing at least nominal values for using in a reconstruction of a parameterization describing a target. The method comprises obtaining first measurement data relating to measurements of a plurality of targets on at least one substrate, said measurement data relating to one or more acquisition settings and performing an optimization by minimizing a cost function which minimizes differences between the first measurement data and simulated measurement data based on a reconstructed parameterization for each of said plurality of targets. A constraint on the cost function is imposed based on a hierarchical prior. Also disclosed is a hybrid model for providing simulated data for use in reconstruction, comprising obtaining a coarse model operable to provide simulated coarse data; and training a data driven model to correct said simulated coarse data so as to determine said sim