Researchers from the Polytechnic University of Catalonia (UPC) and the Spanish Council for Scientific Research (CSIC) have developed an ocean bed seismometer that operates using a data acquisition and storage system based on CompactFlash memory cards such as those used in commercial digital cameras. The machine’s low energy consumption means it can operate independently for two months at depths of up to 6,000 metres.
A group of researchers has presented the new ocean bottom seismometer (OBS) in the magazine IEEE Transactions on instrumentation and measurement. Thanks to its low consumption batteries, the machine can monitor earth tremors using passive seismic techniques for long continuous periods in the ocean depths.
“Until not long ago, OBS were only able to operate independently for periods of 15 days or a month, but this model can carry on collecting data for up to two months,” Shahram Shariat Panahi, one of the report’s authors and a scientist at the UPC’s Department of Electronic Engineering, told SINC.
The seismometer has already been trialled in the waters off Tarragona and Vigo at depths of 1,000 metres, but it is able to withstand pressures in ocean trenches up to 6,000 metres below the surface. During the trials, 20 teams worked in the area to gather information about the thickness of each layer in the ocean floor and the materials from which these were made, down to a depth of 40 kilometres.
The potential of passive seismics
A compressed air cannon is used to periodically simulate small artificial tremors in the form of acoustic waves that are reflected and refracted within the different layers of the sea bed, and are then picked up by the OBS’ sensors. The seismometer converts the analogical signal into digital data, which are stored on memory cards.
The seismometer also performs well because of its small size, low weight, low electronic noise levels, and the use of CompactFlash memory cards similar to commercial ones that act like hard discs, and can store up to 56 GB of information.
The researchers are currently developing 10 more OBS, which they hope will permit even longer independent functioning of up to six months. This project, which will involve new tests around the Spanish coast, will last for two years and will use the new design during seismic refraction campaigns on the sea bed.
- Panahi et al. A Low Power Datalogger based on Compactflash memory for Ocean Bottom Seismometers (OBS). 2005 IEEE Instrumentationand Measurement Technology Conference Proceedings, 2005; 21278 DOI: 10.1109/IMTC.2005.1604353
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