Recovering OBSs

After deploying our grid of OBSs around the Costa Rica Rift, we have finished acquiring our seismic data in this area, and are halfway through recovering the instruments again.

An OBS instrument (ocean-bottom seismograph), showing the concrete anchor on the bottom and the yellow floats on top, with the white strayline strapped on.

Once on the seafloor, the OBSs remain attached to their anchors recording data until they receive a command to be released. Part of the instrument, called the ‘acoustic release’, has a unique code in the form of a series of pings at different frequencies. We send this signal out from the ship when we are near the position of the instrument we are recovering, triggering the acoustic release system to send a very high current through a ‘burn wire’, which will then burn through and release the OBS from its anchor. Yellow floats attached to the top render the OBS buoyant enough to float up to the surface, where its strayline is hooked and the instrument pulled aboard to have its precious data downloaded. 

A set of 16 acoustic releases ready to be dunked in the water for testing, to see if they are receiving the signals from the ship

We’ve also performed some initial processing of both multichannel reflection (from the hydrophone streamer) and the wide-angle OBS data, to check everything's working correctly and do some quality control.

An OBS ready to be deployed by moonlight. Each is fitted with a flag, light and radio to help spot the instrument once it reaches the surface

Wildlife update

We’ve been very lucky with wildlife already on this cruise, with another pod of dolphins spotted, along with a turtle and more flying fish and squid! The boobies that accompanied us on JC112 have also returned, and are sadly recommencing painting the forecastle deck white.