A Noise Model for the German OBS pool

GERRIT HEIN*1, SIMON STÄHLER2, MECHITA SCHMIDT-AURSCH3, CÉLINE HADZIIOANNOU1, ROBERT MARS4

1Institute for Geophysics, University of Hamburg, Germany, 2Institute for Geophysics, ETH Zürich, Switzerland (staehler@erdw.ethz.ch), 3Alfred-Wegener-Institut, Bremerhaven, Germany, 4Leibniz Institute for Baltic Sea Research, Rostock, Germany

Ocean-bottom seismometers (OBSs) allow us to extend seismological research to the oceans to constrain offshore seismicity but also image the marine subsurface. A challenge is the high noise level on OBS records, which is created not only by bottom currents but also by the specific seismometer models used. We present a quantitative noise model for the LOBSTER OBS, which is the main instrument of DEPAS, currently the largest European OBS pool, stationed at Alfred-Wegener-Institut (AWI) Bremerhaven. Studying sensor noise in vault conditions and current sensitivity at an oceanographic measurement mast, we can show that the previously reported high noise level of the instrument is caused by the original sensor (Güralp CMG-40T-OBS) or its housing.

We also show that a strong signal that has been reported between 1 and 5 Hz can be attributed to head- buoy cable strumming. This noise signal can actually be used to estimate bottom current velocities with relatively high precision to a few cm/s.
We provide a current-dependent quantitative noise model that can be used for experiment design in future deployments. We further show that replacing the original sensor with a Trillium compact considerably improves the performance of the pool OBS at moderate cost.

Advertisements