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