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2	Outline Hydrophones: Specifics Acoustic characterization (air) Measurement system Array of hydrophones Audio equipment Array: acoustic characterization Array applications: “Passive mode”: DOA estimation; “Active mode”: Target research and identification Conclusion
3	Hydrophones
4	Array of receivers
5	Audio equipment
6	Audio equipment
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20	"Implementation of a low-cost system..." Implementation of a low-cost system and software, based on a “Not-Uniform Linear Array” is possible; Good agreement between the estimated and theoretical values of array directivity. Good capability of the system to detect real angle of incoming sound (DOA), especially at medium-high frequencies (greater directivity). (Passive sonar) Identification of submerged objects placed in a wide angle under the array is possible. (Active sonar) The linear sine sweep shows high SNR, high immunity to external noise and good capability to penetrate in the sediments.
21	"The authors want to express..." The authors want to express their gratitude to: the company WASS (Whitehead Alenia Sistemi Subacquei) ( http://www.wass.it ) that has supported this research supplying transducers and electronic equipment, and advising the authors in the choice of transducers. Dr. Michele Zanolin (Embry-Riddle Aeronautical University – Prescott (AZ)), who attended some of the measures and provided the sound source used in the characterization of the array.