Fifth International Congress on Sound and Vibration

For a fast moving CROSS-AMBIGUITY FUNCTION Kam W. Lo and Brian G. Ferguson Defence Science and Technology Organisation P.O. Box 44 Pyrmont NSW Australia acoustic source in proximity to a pair of widely spaced sensors, the conventional cross correlation method results in poor time delay estimates because the signal received by each sensor experiences a different degree of time scaling. The correct procedure for time delay estimation in this case is to match the time scales of the two received signals, prior to cross correlating them. In practice, the relative time scale between the two signals is not known a priori and hence it must be estimated jointly with the time delay. This can be done by evaluating the passive wideband cross-ambiguity function. Four different methods are described for computing this function. The most efficient method is applied to synthetic acoustic data which simulate the outputs of three widely spaced microphones during the low altitude transit of a jet aircraft. The resulting time delay estimates are used to calculate the angular trajectory of the aircraft during the transit.