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Questions & Comments
 

FREQUENTLY ASKED QUESTIONS (FAQs)

Q1. Why can't the NEXRAD be reprogrammed to filter out returns from wind turbines?
Q2. What is the NEXRAD Program doing to solve the WTC problem?
Q3. How close is a NEXRAD-based solution to the WTC problem?
Q4. Will Dual Polarization reduce WTC?
Q5. Can we attend local/county wind farm permitting meetings and protest projects that will be too close to our radar?
Q6. Does the DOC, NOAA, or the NWS have any legal or statutory recourse to halt wind farm developments that will severely impact the NEXRAD radar?

Q1. Why can't the NEXRAD be reprogrammed to filter out returns from wind turbines?

REPLY: The NEXRAD’s clutter filter scheme only removes clutter that is stationary, such as buildings, trees, terrain. Unfortunately, both precipitation and wind turbine blades are moving, and the filter is not applied to them. Trying to filter out moving blades will inevitable alter how the radar sees real precipitation. Here’s why. A single radar volume sample (gate) at 30 miles from the radar is approximately a square kilometer. Thus, for a typical wind farm, the radar may receive reflected energy from several turbines within that gate, each with multiple rotating blades. These numerous rotating blades appear similar to precipitation, which is also made up of numerous distributed moving targets. Yes, there are fewer blades than raindrops within a sample volume, but the blades make up for their smaller numbers by reflecting significantly more energy back to the radar. However, the radar has no way to determine the number of targets it is sampling within a particular gate. Also, the reflected energy is constantly changing as the blades change their pitch and orientation relative to radar, with some blades moving towards the radar, some moving away, and some not appearing to move at all (perpendicular). This is analogous to the movement of precipitation within a volume sample. Thus, the reflected microwave energy (signal) from moving turbine blades looks too much like the reflected energy (signal) from precipitation. Reprogramming the signal processor to differentiate between them is a complex problem that may not be solvable. Studies are underway at the University of Oklahoma and other institutions to find a solution. However, at this time there is no known way to filter out turbine blade clutter.

Q2. What is the NEXRAD Program doing to solve the WTC problem?

REPLY: The NEXRAD Program has provided research funds to the University of Oklahoma to devise potential short-term and long-term solutions. Short-term efforts are focusing on automatic identification and flagging of wind turbine-corrupted data. Advanced signal processing techniques, such as non-stationary clutter filtering, are also being explored as sophisticated and robust solutions, but these are long-term efforts. In addition, innovative radar designs, such as adaptive phased array antennas, are being explored as potential solutions. Finally, knowledge-based techniques, which would exploit information (blade phase, rotation speed, etc.) from wind turbines are being conceived. The Atmospheric Radar Research Center (ARRC) at the University of Oklahoma plans to make use of its Electromagnetic Microphysics Laboratory (EML) for this final concept. With the appropriate funding stream, experiments could be conducted to simulate a working turbine within the lab, providing the ability to test knowledge-based algorithms in a controlled setting.

Q3. How close is a NEXRAD-based solution to the WTC problem?

REPLY: There may not be a NEXRAD-based solution (i.e. no signal processing solution). The simplest solutions, such as identifying and flagging wind turbine-corrupted data, are at least 5 years away and they are only partial solutions. Signal processing solutions, in general, are very complicated and are at least 5 years away, assuming an acceptable solution can even be found.

Q4. Will Dual Polarization reduce WTC?

REPLY: We do not know yet. We currently do not have any dual polarization data from wind turbines. However, we are interested in obtaining data to determine if dual polarization shows any promise to reduce WTC impacts on the NEXRAD radars.

Q5. Can we attend local/county wind farm permitting meetings and protest projects that will be too close to our radar?

REPLY: Yes, you can attend the meetings. No, you cannot protest projects. NOAA General Counsel has advised that you may attend these meetings, but you may not protest or try to halt the project. Any comments made need to be factual. The ROC can assist sites in this area.

Q6. Does the DOC, NOAA, or the NWS have any legal or statutory recourse to halt wind farm developments that will severely impact the NEXRAD radar?

REPLY: In short, no. However, the Radar Operations Center has found that many wind farm developers are conscientious and want to do the right thing. The key is making them aware of the impacts to the radar before they have invested significant time and money in the project.