Abstract: A method of obtaining a representative 2D or 3D model of a heterogeneous medium described by multiple physical parameters (such as the impedances of the subsoil in relation to P or S type waves, its density, etc.) from various data. An a priori model with multiple parameters formed from known or estimated isolated values of the physical parameters and the initial model is improved by minimizing a global cost function representative, on the one hand, of the differences between synthetic records giving the response of the current model and the seismic records obtained, and on the other hand of the differences between the current model and the a priori model. These differences are measured in the sense of norms deduced from the a priori information on the uncertainties relative to the data and to the model, and the information can vary from one point of the model to another. The invention has an application for characterization of hydrocarbon reservoirs.