Harmonic phase coupling for battlefield acoustic target identification

Target identification using battlefield acoustic sensor arrays is an important problem for the Army. Acoustic signatures of targets of interest, such as tanks and trucks, exhibit time-varying patterns of harmonic amplitudes that facilitate target ID. In this paper, harmonic phase coupling is shown to also be present in these acoustic signatures though issues remain to fully exploit these relationships for target ID. With all else being equal, frequencies with simple harmonic relationships, such as 2 to 1 or 3 to 2, are preferred to produce stable features. Also, naive use of FFT approaches to estimate phase leads to erratic estimates. Cramer-Rao bounds (CRB) are presented and provide insights into the limitations of the accuracy of phase coupling estimates and suggests the value of developing nonstationary methods