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High hopes for new weather radar fix to 'ignore' wind farm clutter

By Scott Sutherland
Meteorologist/Science Writer
Thursday, August 14, 2014, 3:34 PM

With wind farms cropping up throughout the countryside to feed our need for clean energy, there's one way that they're definitely causing us problems - they can show up on weather radar looking like severe weather, making life difficult for forecasters issuing warnings to keep the public safe.

Rather than tear down the wind farms, since they do represent a very valuable renewable energy source, Environment Canada scientists have developed a new trick in the software that interprets the radar signals, which will hopefully filter out this 'noise' and only show the true weather from now on.

As radar signals expand out from the station, they encounter many different obstacles - trees, buildings and even terrain - which reflect back the signals strongly, contaminating the radar display with 'clutter' that can spoil the view of real weather. Also, this reflecting back of the signals creates a 'blind spot' beyond the object. This is normally avoided by carefully choosing the location of the radar station (King City radar is at an elevation of over 200 metres above the GTA), careful angling of the radar signals so that they are above as many obstacles as possible and getting overlap from different radar stations in the area (although Canadian weather radar coverage is rather sparse for this). 

However, with wind turbines encroaching on radar station 'territory', that is getting tougher to do, as tower and blade can reach 150 metres into the sky - the height of a 35-story building - and farms can combine together to produce significant blind spots.

King City radar visibility map, Credit: Env. Canada

The reason none of these stationary obstacles show up on radar displays is because there is code included in the program that interprets the signals, which instructs the computer to ignore anything that isn't showing significant movement. Since trees and buildings and wind turbine towers don't move around often, except under extreme conditions, they get filtered out of the display. However, since wind turbines have moving blades, this adds in an extra complication.

According to the Environment Canada website, "wind turbines have rotating blades which constantly change their orientation based on wind direction. This rotation is detected by the Doppler radar as an object with velocity. Turbines cannot be filtered out because the blades are moving. This kind of false information can be significantly misleading for forecasters under storm conditions."

The Canadian Press reports that the new changes to the software are coming about in the fall, and Jim Young, Science Liaison for Environment Canada's National Radar Program, told the news agency that he has "very high hopes" for the change to make a difference.

However, it may not be enough to fix the problem in every situation, especially when it comes to extreme weather. To address this particular issue, the government is in talks with energy companies like NextEra Energy Canada, to give forecasters to ability to request that specific wind turbine farms shut down operations when extreme weather is in their area. This would remove any residual radar clutter during critical times, which could even allow the radar software to run faster, since it wouldn't be dealing with added subroutines. A good example of this would be when forecasters are trying to scan storms for small-scale rotations that would denote the potential for a tornado to form.

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