Passive ranging using the fluctuation of target tonal acoustic intensity

The tonal acoustic intensity of the shipping noise will fluctuate with the movement of the target. The fluctuation of two or multi tonal acoustic intensity is used in tonal source ranging. The reason why the acoustic intensity fluctuates with the change of range is the interference of different normal mode. Theoretical relation between the different tonal acoustic intensity which fluctuates with the change of range is derived using the relationship between the horizontal wavenumber difference of normal mode and waveguide invariant in shallow water. Based on the theoretical relation, the range of the tonal source can be estimated using the fluctuation of two or multi tonal acoustic intensity. The reason why the ranging results show high sidelobes level when using the fluctuation of two tonal acoustic intensity and the method which suppresses the side lobes level using the fluctuation of multi tonal acoustic intensity are given. The feasibility of the two methods is verified by simulation and the method using the fluctuation of multi tonal acoustic intensity can effectively suppress the side lobes. Results from the shallow water acoustic experiment show that the range of a fishing boat can be achieved using the fluctuation of multi tonal acoustic intensity when the range can't be estimated from the week continuous spectrum and the mean relative error of the range estimation is 12%, demonstrating the feasibility and robustness of this method.