Wind Power in the UK (PDF). - Sustainable Development Commission

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Wind Power in the UK (PDF). - Sustainable Development Commission

10 Aviation and radarEffects on PSRThe main effect of wind turbines on PSR is dueto the rotation of the blades. Since the bladesare rotating, they may not produce a radarreturn on every sweep of the radar, and inmultiple-turbine wind developments, the radarmay illuminate one turbine on one sweep, thena different one on the next sweep, and so on.This can produce shifting radar returns fromwithin the wind site, sometimes referred to as a'twinkling' appearance on the radar screen. Inmost cases, these effects only occur when thewind development is within line of sight of theradar xxxix .There are three uses for PSR in aviation: for airtraffic control (ATC) around airfields, for area or'en route' ATC, and for military air defence.ATC around airfieldsMost military airfields and commercial airportsare equipped with PSR, which is used bycontrollers to guide aircraft after take-off, toguide incoming aircraft to the runway, and tomaintain separation for aircraft operating in thevicinity of the airfield. For these radar systems,a wind development located beneath thedeparture track, or the final approach track cancreate particular problems.For military airfield radars, the MOD requestsconsultation on projects within 36nm (67km).Whilst controllers may guide aircraft onestablished tracks, aircrew regularly require todeviate from these tracks due to the nature ofthe military task. Therefore, an objection islikely for any wind energy project within 36nmwhich is determined to be visible to the radar.Unlike civil aircraft, military air movements arenot confined to defined routes therefore fullview of airspace is required for air traffic control.En route ATCControl of aircraft in the en route phase of flightis carried out using a network of long-rangeradars, located mostly on hilltops stretchingfrom Devon to Shetland and operated by NATS.Most of these aircraft are flying in controlledairspace and have SSR transponders, so inprinciple these radars are not as vulnerable tothe effects on PSR outlined above. Howeverprimary radar returns from a wind developmentlocated underneath a busy airway may clutterthe screen and make it more difficult forcontrollers to differentiate their traffic from theclutter.NATS en route radars are a frequent source ofobjections to wind developments in the UK dueto their generally prominent positions and theirlong range. However, despite the large numberof projects receiving initial holding objections, asignificant number are subsequently determinedto have little or no significance for ATCoperations.Air defence radarThe MOD safeguards seven air defence radarsites around the UK coastline. The air defenceradars are at the heart of an air surveillancesystem which aims to provide unbrokencoverage of UK airspace to enable the detection,tracking and identification of all aircraftmovements down to the lowest practicablealtitude and to deny a clandestine air approachto the UK mainland.The Government perceives an increased risk ofinternational terrorism and as such air defencexxxixCertain weather conditions may bend radar energy over the horizon on an irregular basis.100 Wind Power in the UK sustainable development commission

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