In accordance with an aspect of the present application, a system is provided for crack monitoring in a structure of interest, comprising means for extracting wave modes existing in a frequency interval of interest, means for finding a source of emission on the structure of interest, means for correcting for dispersion to reconstruct an original ratio of wave modes at the source of emission, and means for correlating the original ratio of wave modes to a crack depth.One advantage of this solution in contrast to prior art techniques is that no a priori knowledge on propagation speed is necessary since actual wave modes can be detected from dispersion relations of wave modes, e.g. Lamb waves at a fixed frequency band in accordance with their calculated speeds. Decentralized acquisition and processing, i.e. monitoring a structure from a localized area, is an important feature of this solution, consequent to which, the data transfer and storage are reduced substantially.