Plattform Platform	Reise-Nr. Cruise-No.	Zeitraum Period	Projekt Project	Arbeitsgebiet Working area
Alkor	AL386	16.03.2012 - 24.03.2012	BORA -BERECHNUNG VON OFFSHORE RAMMSCHALL	North Sea

Fahrtleiter Chief Scientist	Institut Institute	Auslaufhafen Port of departure	Einlaufhafen Port of return	Stationskarte Station map	Schiffsroute Trackchart
Rabbel Wolfgang	Institut fur Geowissenschaften - Abteilung Geologie	Kiel	Kiel

Ziel der Reise / Objectives of Cruise:

The objectives of the cruise were (1) to determine the seismic sediment structure of the seabed of offshore wind farms to a depth of approx. 30 m before the start of construction work and (2) to measure the intensity of ground-coupled underwater sound caused by ramming foundation piles during the construction of wind turbines. This part of the piling noise is not excited directly in the water column, but it is caused by the deformation of the ground during piling, propagates from there as a seismic wave below the seabed and couples back into the water column as sound. The seismic sediment structure was required in this study to create a subsurface model that can be used to simulate the propagation of ground-coupled underwater sound. The investigations were performed in two working areas within the BARD 1 wind farm and east of the ALPHA VENTUS wind farm. The measurement program included high-resolution reflection seismics to resolve the geological structure and measurements with Scholte waves to estimate the shear modulus at the sea floor. The reflection seismic measurements were carried out with a boomer source. Several parallel profiles were measured over a distance of 50 m over an area of 500 m x 500 m. In addition, a long reflection profile was recorded, on which shear wave velocities of the soils were determined from Scholte wave recordings. The Scholte waves were generated with an airgun and recorded with five seafloor seismometers. On the basis of the data collected, it was possible to determine that around 1/3 of the sound intensity measured during ramming in the water column comes from ground-coupled waterborne noise. The seismic measurements were combined with a marine geophysical practical course, which is part of the curriculum of the geophysical courses at Kiel Universit. With this practical course, the students were given general knowledge of work processes on board as well as technical knowledge, especially in the implementation and evaluation of marine seismic reflection measurements and the application of seabed seismometers and hydroacoustic measurement methods.

Messungen / Measurements