Clear harmonic components at multiple s of 0.5 Hz were observed on the majority of the spectra with particular peaks at 0.5, 3.0, 4.5, 6.0, 7.5 Hz and higher frequencies at levels of up to 250 nanometres s -1 ( 0.25 microns s -1 ) and general levels of 50 to 80 nanometres s -1 (Figure 6) . The presence of so many harmonics which are multiples of the blade passing frequency and the clear attenuation of signal amplitude with distance es pecially for the 7.5 Hz component is a prima facie argument that the signals are being generated from the wind turbines an d although the levels are small they can easily be detected on appropriate sensors. The 1.5 Hz component is not the strongest harmonic as might ha ve been suspected.