Last Updated: 04/12/2013*
The wind turbine interference problem has drawn considerable attention in recent years. A number of mitigation approaches have been proposed and pursued, ranging from special anti-reflective coatings on wind turbine blades, to the fielding of additional gap-fill radars in the vicinity of the air traffic control (ATC) radar site, to data suppression algorithms that edit out target detections or inhibit track formation in wind farm areas. These solutions have demonstrated only limited success to date, as they tend to mask the problem instead of solving it; moreover, most involve excessive cost as well as further technology development.
ATC radars generally fall into two categories: primary surveillance radars (PSRs) that detect echoes of transmitted electromagnetic pulses to identify targets in the surveillance area, and secondary surveillance radars (SSRs) that send out coded messages and receive replies from aircraft equipped with appropriate electronic transponders. The data collected by PSRs and SSRs is usually combined in an automation system that generates an airspace picture used by controllers to maintain separation between aircraft. Raytheon is a world supplier of PSRs, SSRs and automation systems.
The wind turbine RF reflection problem significantly affects PSRs. PSRs find targets principally by discriminating moving objects within the imaged space using the Doppler shift imparted to the radar pulse echo by the target. Rotating wind turbine blades can produce echoes with the same Doppler frequency offsets as aircraft. As a result, the radar echo from a wind turbine looks like a real aircraft to the radar. This may potentially result in the generation of many false tracks, the dropping of real tracks and the displacement of real tracks to false locations on the air traffic control display. Unless this problem is solved, these effects can result in dramatic restrictions being imposed on air traffic. The construction of new wind farms may even compromise flight safety. Large tracts of airspace above wind farms are currently designated as "no-fly zones" because local ATC radars are effectively blind in these areas. In the U.K. alone, more than 30 gigawatts of wind power are currently prevented from coming on-line because of objections raised by air navigation service providers.
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