On the infrasound emission generated by wind turbines

Aerodynamic infrasonic signals generated by wind turbines can be detected by highly sensitive micro-barometers showing spectral peaks at the blade passing harmonics, which are above the background noise level. As infrasound is one of the four verification technologies for the compliances with the Comprehensive Nuclear-Test-Ban Treaty (CTBT), decreases in detection capability for dedicated infrasound arrays have to be avoided. Therefore, preventing such decrease is particularly important for the two German infrasound stations IS26 in the Bavarian Forest and IS27 in Antarctica, which are both part of CTBT’s International Monitoring System and have to meet stringent specifications with respect to their infrasonic ambient (natural and anthropogenic) noise levels. In 2004, micro-pressure variations along a profile starting at a single horizontal-axis wind turbine were measured during a field experiment with mobile micro-barometer stations. As one of the results, a minimum distance to wind turbines for undisturbed recording conditions at infrasound array IS26 was estimated based on numerical modelling, validated with this dataset. Both observations and modelling were in agreement with the literature, where infrasonic signatures of wind turbines are reported at distance ranges up of tens of kilometres. Nevertheless, for broadening the dataset further infrasound measurements at two wind parks with modern large wind turbines have recently been carried out in Lower Saxony and Saxony-Anhalt, respectively. Here various instruments (micro-barometers, microphones, pressure sensors) have been deployed in a comparative manner. We will give an overview of these campaigns, followed by first results of our analysis and interpretation.