Passive acoustic detection of a small remotely operated vehicle

Abstract

This project quantifies the feasibility of passive acoustic detection of a small commercial off-the-shelf (COTS) remotely operated vehicle (ROV) by experimentally characterizing the acoustic signature and hydrodynamic flow associated with the motion of ROV. Three experiments are conducted as parts of this characterization in this project. These trials are conducted in a small laboratory test tank, a larger outdoor test tank and a shallow-water coastal ocean environment. The laboratory tank test consists of a stationary hydrophone to detect the acoustic emissions, while simultaneously measuring the flow field using particle image velocimetry (PIV) system. Based on a variety of maneuvers in the test tank, the experiments are quantified by the acoustic signatures of the ROV. Also, we predict the capabilities of acoustically detecting an ROV in typical ocean environments such as shallow-water, ports and harbors, and deep-ocean environment. In addition, this thesis reports the results of a series of underwater detection trials in the field to verify the laboratory demonstration and analytical moderns. The intention is to experimentally measure the signal-to-noise ratio (SNR) of the ROV acoustic signature, as a function of distance between the ROV and acoustic receivers in the shallow-water ocean environment. On the basis of experimental analysis, we present that the most significant contribution for ROV acoustic detection is from electric motors with signal frequency range of around 400-500 Hz. The detectable distance range with ambient noise at 116 dB re 1 uPa is between 15 m and 22 m away in a noisy littoral environment. Combined with the experimental analysis, we state the comparison between the acoustic predicted levels of the ROV with the measured results. Finally, this project demonstrates the feasibilities of acoustical detection of a small ROV in the port environment. As a result, we conclude the experimental studies with later highlights and future research.