1. A method for identifying a source of electromagnetic signals comprising the steps of: receiving an electromagnetic signal emitted from the source; providing a finite state automaton for modeling the source, the finite state automaton comprising a finite set of states and a set of transitions from state to state that occur in dependence upon an input signal, the finite state automaton for producing a sequence of output symbols from an output alphabet in dependence upon the state transitions, such that the sequence of output symbols corresponds to the received electromagnetic signal emitted from the source; hidden Markov modeling of the finite state automaton and determining parameters of the hidden Markov model such that a sequence of observation symbols or multivariate observations produced from an observation alphabet or a continuous distribution by the hidden Markov model is equal to the sequence of output symbols; and, identifying the source in dependence upon the determined parameters of the hidden Markov model.