Underwater noise emission from the NOAH’s drilling operation at the narec site, Blyth, UK

Abstract

In November 2011, the National Renewable Energy Center (narec) launched their offshore wind demonstrator project 'round 3'. Narec commissioned SeaRoc to undertake the deployment and drilling operation of the Narec Offshore Anemometric Hub (NOAH). On this occasion, the Bio-Acoustic Research Consortium combining university and industry researchers conducted a study on noise and marine mammal occurrence before, during and after installation of the Noah platform. This paper describes the noise emission from the installation of the NOAH's jacket. The team preliminary undertook underwater ambient noise measurements at different seasons, and locations at the site. The results of these measurements are discussed in this paper. The pin pile drilling itself occurred at 3 nautical miles offshore Blyth and at a 40 m depth. The Newcastle research vessel Princess Royal was positioned at 500m and 3 nautical miles from the NOAH's drilling. The engine and all electronic equipment on board, such as sonar and depth sensors were switched off during the pin pile drilling noise monitoring. At each position, a self-recorder hydrophone was deployed from a semi-submersible drifting buoy to reduce the effect of the swell (sea state 3), which could have affected the quality of the recordings. The deployment from a drifting buoy also has the advantage of reducing mechanical noise from the boat as the buoy drifts freely away from the vessel. Each recording lasted between 5 and 10 minutes and the buoy was then retrieved for another deployment at the next position. Sample measurements were taken at approximately 10 m depth and at a sampling rate of 312 kHz and 24 bits resolution. Matlab was used as a post-processing tool to analyse the data. Each file was processed on a 2 min average using a FFT of 216 points. The in-house code displays Sound Pressure Level (dB re1µParms) and Pressure Spectral Density (dB re1µParms2/Hz) with a 1Hz resolution. The results demonstrate that the noise coming from the pin pile drilling was relatively low in comparison to the background noise. At 500 m from the drilling, the noise appears to be only 10 to 20 dB higher than the background noise over the frequency band 10 Hz to 50 kHz. Higher energy was concentrated between 100 Hz and 600 Hz reaching up to 100 dB re1µParms.