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High-Sea Acoustic Monitoring

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CONTENTS

General information

Instrument description

Data

Contacts

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General information

Within the framework of the Universe Sciences Observatory, our goal is to maintain on a long-term basis two acoustic observatories:

  • OHA-SIS-BIO in the Southern Indian Ocean

  • HYDROMOMAR in the Central Atlantic Ocean

Each observatory represents a network of continuously-recording moored underwater hydrophones capable of functioning autonomously for up to 24 months. Such a network allows monitoring of low-level seismicity processes associated to active areas of the ocean bottom (such as spreading ridges, transform faults, deformation areas, hydrothermal sites). Due to their low magnitude, the underwater earthquakes are rarely recorded by the land-based seismic stations. However, they produce acoustic phases of appreciable magnitude, called T waves, which propagate over great distances without significant attenuation in the Sound Fixing and Ranging (SOFAR) channel. The T waves are recorded by the hydrophones positioned in the axis of the SOFAR channel. Our objective is to acquire long-time series which would be most representative of the tectonic and magmatic processes happening at the active areas.

Frequency range of our instruments (0-120 Hz) also allows us to record the vocalizations of several species of large whales, for example Antarctic Blue whale and Fin whale. This gives to the whale biologists an invaluable opportunity to study seasonal behavior of the whales as well as estimate how much the whale population recovered since the ban on the whaling in the 1960's.

We also work on:

  • the development of the new tools for automatic processing of large volumes of data (automatic signal classification)

  • the problem of extracting the information on an earthquake from generated T waves. This study involves conducting advanced numerical simulations whose results are then compared with T waves recorded by the hydrophones.

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Instrument description

Pressure variation is continuously recorded on a 24-bit basis at a sampling frequency of 240 Hz. This amounts to approximately 24 Gb of data per year. The internal clock precision is 10-8 seconds. Depending on the number of Lithium batteries, the instrument is able of functioning from 18 to 24 months.

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Data

The pressure variation is recorded on 24-bit basis with the sampling frequency of 240 Hz. The hydrophones with the new data are recovered every year (sometimes every two years depending on the availability of the research vessel). Once on board the ship, the internal clock of the hydrophone is synchronized with the GPS clock in order to know precisely the clock drift. The hydrophone is then reconditioned and redeployed during the same oceanographic campaign. Our data are thus logically divided into the periods between deployment and recovery as listed below:

OHA-SIS-BIO

OHA-SIS-BIO-1 (2009/12-2011/01)

OHA-SIS-BIO-2 (2011/01-2012/01)

OHA-SIS-BIO-3 (2012/02-2013/02)

OHA-SIS-BIO-4 (2013/02-2014/02)

OHA-SIS-BIO-5 (2014/02-2015/01)

OHA-SIS-BIO-6 (2015/02-2016/02)

HYDROMOMAR

HYDROMOMAR-1 (2010/06-2011/08)

HYDROMOMAR-2 (2012/08-2014/06)

HYDROMOMAR-3 (2014/06-2016/06)

Contact

Those interested in our data are welcome to contact:

  • OHA-SIS-BIO : jean-yves.royer [at] univ-brest.fr, alexey.sukhovich [at] univ-brest.fr

  • HYDROMOMAR: jperrot [at] univ-brest.fr

 

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