Authors developed a passive sonar system for searching rocket boosters with acoustic beacons, which will be launched by JAXA with H2A rocket, detached from the rocket, and sink under deep sea. The system consists of an underwater unit that can be operated at 6500m deep and an onboard unit with signal processing and display functions. The underwater unit is mounted on ROV which is towed by a mother ship at 500～1000m above the bottom. The system provides detection and a localization functions. The detection is realized by using two linear, multi-element, hydrophone arrays receiving acoustic pulses radiated from acoustic beacons from both sides, multi-beam formers, and waterfall displays. The localization is realized by using a 4-element planar hydrophone array and an SSBL acoustic positioning signal processing. The acoustic signals received by the hydrophone arrays are digitized and transmitted to the onboard unit via an optical fiber cable. The onboard unit consists of two PC's, which execute signal processing and display functions.
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