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Small aircraft – manned or unmanned – can play a significant role in near-shore operations that include transporting vital items – for instance, blood, food supplies – to ships in distress. Of course, harbour security is another task that can be fulfilled by such air operations. Given that the sound emitted by these fixed wing aircraft is predominantly in propeller rate harmonics, a time-frequency portrayal of the acoustic signal can help glean vital information on the kinematic parameters of the aircraft. The passive means of detecting and possibly localizing the aircraft is important if the aircraft location is needed in near real time, in case of link loss in the case of an UAV. Herein we present results of experiments carried out with an UAV in flight over the Arabian Sea and a manned aircraft over the Bay of Bengal. An array of microphones and an early version of an acoustic vector sensor were positioned aboard the deck of a ship in each case. The sensor signals recorded on a digital tape unit were post processed using time-frequency signal processing methods. Intensity and particle velocity cross correlation based algorithms were investigated towards estimating the direction –of – arrival information. The campaign overview and signal processing challenges encountered are explained in the paper.
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