2.1. Measurement MethodologyMeasurements of wind farm construction noise were performed from a drifting rigid hull inflatable boat (RHIB) in the vicinity of the piling site [7]. To avoid interaction with the hydrophone, the engine, Belinostat HDAC radar, and echosounder were turned off. The geographic position and time of measurement were recorded with a handheld GPS GARMIN GPSMap60 at a frequency of one position every 5 seconds. The clock of the recorder was synchronised beforehand with the GPS-time (UTC). At the start and the end of each measurement a reference signal was recorded. Several recordings of few minutes each (1 to 5min.) were performed at different locations on September 26 2009 (monopile A02) and January 15 2010 (monopile B10) at the Blighbank and on the May 11 (jacket CG3) and the of July 12 2011 (jacket CB6) at the Thorntonbank site (Table 1).

Weather conditions encountered during fieldwork featured a wind force of 1�C3BF and a sea state of 1 to 2.Table 1Geographic position, peak level (Lz�Cp), and distance from the piling location of the underwater noise measurements at the Blighbank site (monopiles A02 and B10) and at the Thorntonbank site (jackets CG3 and CB6).2.2. Acoustic Measurement EquipmentFor every measurement, a Br��el & Kj?r hydrophone (type 8104) was deployed at a depth of 10m. A Br��el & Kj?r amplifier (Nexus type 2692-0S4) was connected between the hydrophone and the recorder in order to allow for an amplification and filtration of the signal. A reference signal was used together with the output sensitivity of the Nexus to calibrate the amplitude of the recorded signal.

The signal was recorded using an audio MARANTZ Solid State Recorder (type PMD671). It was operated with the highest possible sampling rate of 44100Hz. The signal was recorded in WAVE format (.wav) on Compact Flash cards of 2GB (Sandisk Ultra II). Batteries powered all equipment. 2.3. Response VariablesIt is very common in underwater acoustics to use values expressed in a logarithmic scale (decibels). In order to characterize extreme level values of a transient signal like the one associated with pile driving the peak sound pressure level is often used. This terminology is not totally unambiguous and we prefer to use Lz?p that is defined by [9] in??dB??re??1?��Pa.(1)For impulsive sound, however,?asLz?p=10log?10pz?p2pref2 the unweighted SEL better characterises the energy Drug_discovery produced by a given stroke, extracted from a complete piling event. SEL is computed as defined by [9].