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22nd October 2008

Holographic Infill Radar offers potential solution for the wind farm radar conflict

• Early tests of Cambridge Consultants' innovative Holographic Infill Radar technology indicate that it can successfully distinguish between turbine blades and other moving targets

Wind farms have been found to confuse existing radar systems, compromising Air Traffic Control.  This has led to a situation where around 40 wind farm projects - with a combined capital value of approximately £12bn and a potential output of nearly 6GW of renewable energy - are delayed because of objections from the aviation sector.  Although the vision for the UK government's mitigation strategy - the Aviation Plan - states that "there is no universal solution" to the issue, tests are now indicating that Cambridge Consultants' proposed solution, based on its Holographic Radar technology, can successfully distinguish between wind turbine blades and aircraft.  We believe it is the ‘silver bullet’ the industry is looking for.

Tests of a prototype Holographic Radar system at Ecotricity’s 66m diameter 1.5MW turbine at Swaffham in Norfolk have provided a proof of the principle, with a small-scale system discriminating effectively between the turbine and a moving target.  Further tests are planned with a scaled-up system of the same instrument and moving airborne targets, before a full-scale system is developed for testing at the site of a large wind farm.

Craig Webster, Head of Cleantech at Cambridge Consultants comments, “The vision statement for the Aviation Plan reflects the consensus of the parties that created it and is based on what was known at the time of its formation. However, the statement does not reflect what could be achieved by innovation, and does not appear to allow for the possibility of a solution like ours … a universal solution that could enable the large scale generation of renewable wind energy.”

Holographic Radar is a non-scanning, continuously tracking 3D radar that can discriminate between turbines and aircraft based on easily observable differences in their behaviour.  Current Air Traffic Control radars can detect an object’s movement but can’t resolve speed very well.  If you know the speed as well as the position it is relatively easy to tell the difference between a turbine, which has moving blades but doesn’t change position, and an aircraft, which has a clear correlation between its position and speed over time.  Because transmission and reception are complementary rather than symmetric as in scanning radars, Holographic Infill Radar provides persistent illumination of the field of view with sufficient RF bandwidth and return signal sampling to resolve and measure an object’s motion at fine scale, as well as its range and direction.  This enables it to effectively discriminate turbine clutter at the level of linear signal processing.

“Our solution works because we get to the root of problem: Acquiring continuous information about every target,” comments Gordon Oswald, creator of Holographic Radar at Cambridge Consultants and architect of the current development.  “Current radar systems scan the surveillance zone, emitting a pulsed beam and detecting reflections of moving objects.  Because the sampling period is too short and the interval between scans too long, speed - or Doppler - resolution is poor and the Doppler spectrum is aliased, making it impossible to separate the target from the turbine using any analytical processing technique.  Scanning radars, while excellent at detecting aircraft over long ranges and wide areas, are simply not suited to this task.  That’s where a supplementary Holographic Infill Radar will come into its own.”

“Put simply, Holographic Radar is able to tell the difference between an aircraft and a wind turbine because it can see that they behave differently,” explains Craig Webster. “It will classify and report a radar return as a target when it sees that it moves in a way that is impossible for a turbine.  More importantly, when plugged into an existing radar system to provide infill coverage, it will be able to see a target turn, circle, hover or land while in the vicinity of a wind farm, restoring a level of certainty for an Air Traffic Controller that neither scanning radar nor predictive mitigation strategies can offer.”

Cambridge Consultants has made the Aviation Plan aware of the solution and of its proposals for further tests. 

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