Tuesday, May 28, 2013

Poseidon: Leg 1 completed

The Poseidon successfully deployed 38 ocean bottom seismometers (OBS) on Leg 1!

Today they are reloading the ship with 18 more OBS to deploy on Leg 2. The personnel on board will also exchange two Ocean Bottom Instrument Consortium personnel for two GEOMAR personnel.

What is an OBS?

An OBS is an autonomous instrument that sits on the ocean floor and records waves (sound waves as well as other types) traveling through the earth and/or ocean water. All of our Galicia instruments have ocean bottom hydrophones (OBH) to record waves traveling through the ocean (including some types of whale calls!), and a subset of fifty also have geophones to record waves traveling through the sediments and rocks beneath the sea floor. 

The OBS record waves by measuring tiny motions of the earth and sea water, converting it into electrical signals, which are stored digitally. The geophones, data logger, and batteries are stored in a water tight, floating sphere, and the hydrophone is attached to the outside of the sphere. A heavy anchor attached to the sphere enables it to sink to the bottom when it is deployed (sent off into the ocean).

 To pick up the OBS, the ship goes to the location where it was deployed, and a sound signal with a particular frequency is sent out. The OBS replies acoustically, cuts its anchor, and resurfaces. Scientists can then download the data and begin to piece together a picture of the local Earth structure!

Marianne Karplus
28th May

Saturday, May 25, 2013

Poseidon: Very good progress today!

We dropped 17 ocean bottom seismometers today, making 26 in all.  The weather is cloudy but bright.  There is 2-3 m of swell and this is not a very big ship, so when we were steaming eastwards into the weather there was plenty of water arriving on deck.  Later on we turned to the west, which was more comfortable and drier.  Scientist cabins are partially below the water-line and my port-hole gets a regular wash.

Tim Minshull
24th May 2013

Friday, May 24, 2013

Poseidon sails from Vigo!

On 21st May, F.S. Poseidon sailed from Vigo, Spain on the first of three expedition legs to deploy 78 ocean bottom seismometers (OBS) provided by OBIC and GEOMAR.

Seventy-two OBS will be deployed in a grid of 18 x 4 instruments across the 3-D seismic survey box. Six OBS will be deployed on a profile extending farther west, to try to locate the boundary between continental and oceanic crust.

An OBS is deployed. Photo by Dean Wilson.
Gaye Bayrakci, a postdoctoral researcher at the University of Southampton, sent this email update today:

"Yesterday (23/05/2013) the weather was ok. We tested 24 acoustic units first. Then, we deployed 9 OBSs along the regional profile. Before the finish of the day, we tested 24 more acoustic units. Food is good. Thursday is the seaman's day, so we had some cake at 5pm at the coffee break.

"Today (24/05/2013) the weather is darker but its normal for this period of the year in this area. We started at 06am (utm). We just finished the deployment of 8 OBSs on the southernmost profile and reach the eastern end of regional profile. We deployed a 9th OBS here and now we are heading westward along the regional profile."

The international team of scientists aboard the Poseidon includes two GEOMAR geophysicists, two University of Southampton geophysicists, and five OBIC personnel from University of Southampton and Durham University.

The internet connection on board the Poseidon is not good enough at the moment to post to this blog or send photos, so the above photo is from a separate OBS deployment in the Indian Ocean.

Stay tuned for more updates soon!

Marianne Karplus
24th May 2013