A method, apparatus, and computer program product for identifying dissimilarity indices for a structure is presented. A first test signal is sent into a baseline model of the structure. An estimated response signal to the first test signal sent into the baseline model of the structure is received. A second test signal is sent into the structure. A second response single to the second test signal is received. A value is assigned to a model-based dissimilarity index using the first response compared to the second response.