PACT a bottom pressure based, compact deep-ocean tsunameter with acoustic surface coupling

摘要

The German-Indonsian Tsunami Early Warning System (GITEWS) processes a multitude of information tocomprehensively and accurately evaluate the possible risks inherent to seismic events around Indonesia. Withinjust a few minutes, measurements of the vibration and horizontal movements off the coastal regions of Indonesiaprovide a clear picture of the location and intensity of a seaquake. However, not every seaquake causes a tsunami,nor is every tsunami caused by a seaquake. To avoid nerve-wrecking and costly false alarms and to protectagainst tsunamis caused by landslides, the oceanic sea-level must be measured directly. This goal is pursued in theGITEWS work package ocean instrumentation, aiming at a a highest reliability and redundancy by developinga set of independent instruments, which measure the sea-level both offshore in the deep ocean and at the coast onthe islands off Indonesia.Deep ocean sea-level changes less than a centimetre can be detected by pressure gauges deployed at thesea floor. Based on some of the concepts developed as part of the US DART system, a bottom pressure based,acoustically coupled tsunami detector (PACT) was developed under the auspices of the AWI in collaboration withtwo German SME and with support of University of Bremen and University of Rhode Island. The PACT systemrecords ocean bottom pressure, performs on-board tsunami detection and acoustically relays the data to the surfacebuoy. However, employing computational powers and communication technologies of the new millennium, PACTintegrates the entire sea-floor package (pressure gauge, data logger and analyzer, acoustic modem, acoustic releaseand relocation aids) into a single unit, i.e. a standard benthos sphere. PACT thereby reduces costs, minimizes thedeployment efforts, while maximizing reliability and maintenance intervals.Several PACT systems are scheduled for their first deployment off Indonesia during 2009. In this presentation,the technical specifications and results from extensive laboratory and at-sea tests are shown.