This talk describes the MITRE Undersea sounding experiment (MUSE16) conducted in Narragansett Bay from September 12-23, 2016, where acoustic communication, localization waveforms, and signal processing techniques were explored. This experiment utilized newly developed acoustic buoys which were designed and built by the University of Rhode Island (URI) Ocean Engineering Dept. in collaboration with the MITRE Corporation. The buoys use Global Positioning Satellites (GPS) for localization and time synchronization and are capable of both transmitting and receiving acoustic data in the range of 8-18 kHz. The buoys were designed to further research in the areas of acoustic communications, channel modeling, and continuous active sonar (CAS). For the communication and channel modeling experimentation, modulated M-sequences of various sequence length were transmitted to explore channel characterization and communication enhancements. For the CAS experimentation, Linear Frequency Modulated (LFM) chirps of various bandwidths and center frequencies were explored as well as utilization of several underwater targets. A description of the prototype buoys including hardware, software, experimental setup, types of data collected, as well as some initial results will be discussed.
There is a growing need for real-time monitoring of marine life and floating debris during a wide variety of commercial operations. These include seismic exploration for oil and gas, explosive removal of offshore structures, pile driving for the installation of marine structures including offshore wind farms, and the operation of tidal turbines and wave power generation devices. Active acoustics is likely the best method for monitoring where there is a high-danger region with a limited range around the activity. The SSI Swimmer Detection Sonar Network was originally designed as a human swimmer and diver detection and tracking system. However, extensive trials have demonstrated that the system is also capable of tracking marine life ranging from a large fish or marine mammals to schools of smaller fish. Analysis of the detection characteristics and movement behavior of marine life is being conducted as a means of tracking and classification at ranges out to roughly 500 m. Real-time identification and tracking over time may also provide insight into the habituation of marine life to these facilities in addition to serving as a protective measure. [Research supported by ONR SBIR.]
The ability to conduct surveillance and tracking of targets over a wide area necessitates the use of a distributed sensing network and an appropriate processing scheme. One such technique that may be appropriate for the target tracking problem is continuous active sonar (CAS). In September 2016, an experiment was performed in Narragansett Bay, RI, to assess the performance of CAS for tracking a single unmanned underwater vehicle (UUV). PN sequence-coded chirps and LFM pulses of various bandwidths and center frequencies were transmitted from one transducer and received at two hydrophones in different locations. Following the experiment, several range-doppler sidelobe reduction techniques were experimented with to improve target detections and range-doppler estimations. During processing, waveform properties critical to sidelobe reduction performance were identified, and new waveforms have been chosen which exhibit these properties. A new experiment will be conducted in the coming months to demonstrate the performance of these waveforms, and results are expected to show improved detections and range-doppler estimations for various targets.
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