Pressure ratio and phase difference in a two-microphone system under uncertain outdoor sound propagation conditions

Predictions of outdoor sound propagation in uncertain conditions are a challenging task. Evidence suggests that using more than one receiver can reduce the effect of uncertainties. This paper studies via numerical simulations the effects of uncertainty in the source/receiver geometry and impedance ground condition on the sound pressure ratio recorded using the two-microphone method. A Monte Carlo method is employed to study the effect of uncertainties in the range and ground parameters. The range and frequency are found to be key parameters which control the resultant probability density function for the absolute sound pressure ratio and phase difference. The introduction of small uncertainty only matters if the uncertainty is present in the distance between the source and receiver. Uncertainties in the impedance ground are found to have a negligible effect. The sound pressure ratio is affected by the uncertainty more strongly at a shorter range. These findings pave the way to the development of more robust methods for outdoor acoustic source localisation and identification from two-microphone data.