Wind turbine clutter mitigation for weather radar by means of telemetry

Wind energy has undergone extremely fast growth in the past few years in the form of proliferation of wind farms across America. The reflection from wind turbines, so called wind turbine clutter, is almost immune to current clutter mitigation strategy due to its complicated dynamic spectral characteristics. The rotation of turbine blades might cause continuous contamination of Doppler spectra due to velocity aliasing. The clutter contamination is so strong compared to the weather signal that not only the wind farm area itself, but also the sector blocked by wind farm is contaminated due to multipath reflection and attenuation.

In order to give an insightful study on how wind turbines impact weather radar operation and to establish proper models so that wind turbine clutter can be mitigated by means of signal processing, a unique scatterometer system has been built at the Atmospheric Radar Research Center (ARRC) of the University of Oklahoma. The system includes two major parts: the first is an X-band, dual-polarized pulsed radar emulator. The emulator has a range resolution of better than 2 meters in order to meet indoor measurement requirements and adjustable Pulse Repetition Time (PRT) to keep the Doppler spectrum from aliasing as the blade rotation rate varies; the next part is a sophisticated computer-controlled turbine model which has been specially manufactured for a laboratory-based measurement. Orientation and blade rotation rate can be precisely controlled. Both static and dynamic measurements are taken in an anechoic chamber and time series are collected from various scenarios. It shows that for a single wind turbine, given enough a priori and in situ information (dimension, blade rotation rate, and orientation of the blade plane with respect to radar line of sight), it is possible to estimate the Doppler spectra of a spinning wind turbine and mitigate it by signal processing.

Currently, many wind turbines in field are able to provide telemetry information, in the form of sensors which measure blade orientation and velocity. It is proposed that once such information is available in real time to weather radar operators, it could be applied to the proposed models to accurately estimate the interference generated by the turbines on a scan-to-scan basis. Adaptive clutter mitigation would significantly improve the quality of weather data in the presence of wind turbine clutter.

Future study will be performed on estimation of echo signal from multiple turbines. The interaction between adjacent turbines and the multi-path effect caused by reflection bouncing from ground will be studied. As most weather radars work with Volume Coverage Pattern (VCP) scan, the possibility of wind turbine clutter mitigation with shorter observation time will also be studied in the future.