Application of Near-Field to Far-Field Transformation to Doppler Features From Wind Turbine Scattering

The near-field to far-field transformation (NFFFT) algorithm from Mensa and Vaccaro is applied to obtain the far-field Doppler signatures of wind turbines based on near-field measurement data. A set of angular window and sampling criteria are derived to aid in the data collection and processing. Simulations are performed to demonstrate the effectiveness of the NFFFT and sampling criteria. Near-field measurements are made of a three-arm wire turbine model and a small commercial turbine. The NFFFT is applied to recover the far-field backscattering. The NFFFT is shown to effectively correct the Doppler features from the wind turbine scattering. The measurement results are corroborated with near-field and far-field simulations.