Assessing the seismic wavefield of a wind turbine using polarization analysis

Ambient seismic noise can often be seen as problematic but with the right analysis can act as a tool to image the Earth. Wind turbines are known to generate low frequency vibrations; however, the wave types that are generated are currently unknown. Characterizing these vibrations will allow wind turbines to be used as a seismic source and be of value to geotechnical applications and seismic interferometry. This paper uses polarization analysis of the seismic wavefield around a small wind turbine to identify the type of wave being generated by the turbine and to clarify the source. The seismic data recorded 190 m from the wind turbine are processed using a window length of 0.1 s and bandpass filtered on a selection of frequency ranges. Polarization analysis is performed for two different wind speed ranges, in order to show the variation of wave characteristics between operational and non-operational modes of the wind turbine. Polarized surface waves are identified as the predominant wave type at blade rotation harmonics, making this work particularly relevant to multichannel analysis of surface waves and seismic interferometry. Copyright © 2017 John Wiley & Sons, Ltd.