Estimation of the Trajectory of an Acoustic Source

This paper develops a method for estimating the linear flying trajectory of a turboprop or rotary-wing aircraft based on narrow-band passive acoustical technique, which measures the instantaneous frequency of the acoustical signal emitted by the target and received by Acoustic Vector Sensor (AVS) placed on the ground. AVS consist of one microphone and three vector sensors orthogonal to each other. The received instantaneous frequency varies due to the acoustical Doppler Effect under the condition that the target flies at a constant velocity and the trajectory is a straight line. A four parameter model was developed to describe the aircraft trajectory. The four parameters are the target's travel speed, the source acoustical frequency, the time at which the target get to the closest point of approach (CPA) to the sensor, and the CPA slant range to the sensor. Nonlinear least square theory was used to estimate these parameters. The three dimensional AVS consists of three orthogonally placed particle velocity sensors and one sound pressure microphone. The four parameters mentioned above are measured using microphone. The particle velocity sensors are used for finding the direction of acoustic source.