Experimental Tracking of Aerial Targets Using the Microflown Sensor

Abstract

Determining target bearing based on a passive acoustic signal typically relies on beamforming the signals from an array of sound pressure sensors. A major drawback, however, is the proportional increase in array aperture when dealing with low frequencies, such as the lengthy towed arrays used for anti-submarine warfare. This thesis demonstrates the use of a single acoustic vector sensor (Microflown Ultimate Sound Probe (USP)) to derive the target bearing by processing both the pressure as well as particle velocity information of an acoustic wave. Field experiments were set up to track commercial aircraft during their final approach before landing. Despite healthy signal-to-noise (SNR) ratios, significant challenges were faced in accurate real-time tracking. Post-processing frequently achieved better results, but required the beamformer to process a broader range of frequencies (typically 300-1000 Hz), instead of focusing on narrowband energy peaks. This was attributed to the effects of noise and bottom reflections (mainly from the concrete ground), as implied by the distinct Lloyds mirror patterns in the spectrograms. Notwithstanding, additional information such as target altitude and horizontal distance at the closest point of approach (CPA) could be determined from analyzing these patterns.