Because of the nature of acoustic sensors and preprocessing steps, acoustic energy is typically presented in the form of a power spectrum spanning a particular frequency range. The low frequency end of this range is often higher than the actual (fundamental) frequency of the emitter. Instead, what is detected is some subset of the harmonic frequencies associated with the fundamental frequency.
This leads to an approach consisting of several steps: extraction of harmonic frequencies, association of harmonic frequencies into correlated sets, determination of the fundamental frequency associated with the harmonic set, identification of the acoustic source, and identification of the platform containing the source.