INNOVATION & NEW TECHNOLOGY FEATURE
INNOVATION TO MORE ACCURATELY ASSESS THE IMPACT OF WIND TURBINES ON AVIATION STAKEHOLDERS
Aerostat Surveys Ltd is a new company that hopes to change the way the impact of many wind turbines on aviation is assessed though the innovative use of technology.
FORMER QINETIQ AND CAA AIR TRAFFIC SYSTEMS ENGINEER ADRIAN CLOUGH, EXPLAINS...
It is not uncommon for those in the wind energy sector to come up against objections to planning applications from Aviation stakeholders, and these issues can sometimes be ‘show stoppers’. Wind turbines have the potential to cause significant problems for aviation stakeholders; they can interfere with radar, navigation and communications systems, or present a physical obstruction that impinges upon an airport’s safeguarded volume of airspace.
CONSTRAINTS, COST AND COMPLEXITY Whilst flight paths can be changed, radars repositioned, and aircraft re- routed around wind turbines, all of these solutions present aviation stakeholders with additional constraints, cost and complexity. There are cases where the above solutions have been implemented, however as a rule, many aviation stakeholders are concerned about the need for a consistent approach to wind turbine planning applications that does not result in their own operations being compromised.
AIRPORT PROXIMITY
For proposed turbines that are more than 15km from an airport, any objection is likely to stem from a belief that the wind turbine will be ‘visible’ to aeronautical radar, navigation or communications facilities. The aviation stakeholder will almost certainly have used a software tool to predict the path loss between the aeronautical system (e.g. primary radar) and the proposed wind turbine structure. This in turn enables the strength of the aeronautical signal incident on the wind turbine’s structure to be estimated, and any consequential effects (e.g. clutter, bearing errors or shadowing etc.) to be quantified.
COMPUTER MODELS The problem with computer models is that they are only as good as the information they are given. For example, all digital elevation models have a limited resolution and can ‘miss’ some of the high spots along the signal path. In the real world, there are literally thousands of additional physical objects (buildings and structures, foliage, vehicles etc.) and other factors such as the actual performance of an installed antenna (rather than the manufacturer’s specification) that can influence the amount of signal reaching the wind turbine.
However, aeronautical stakeholders using a computer model to determine whether a wind turbine will be visible to aeronautical systems will not be concerned about such factors, as the result provided will be suitably conservative – in other words, these assessments should predict more signal than would exist in the real world. Whilst this may not be a problem for aeronautical stakeholders, the problem with this approach is that there will inevitably be objections to some wind turbines that if built, would not be ‘visible’ to aeronautical systems as a result of real world factors. At the same time, if incorrect parameters are used in the modelling, it is also possible for predictions to be overly optimistic, and this can lead to problems downstream for the aviation stakeholder.
AEROSTAT SURVEYS’ SOLUTION Recognising the limitations of desktop radio propagation modelling assessments, Aerostat Surveys has developed an innovative way to measure the actual strength of aeronautical signals at a given point-in-space, thereby ensuring that all factors are taken account of in the assessment.
Extremely lightweight signal measurement equipment is carried by a small tethered helium balloon to heights of up to 500 feet above the site of the proposed wind turbine. Precise data relating to the frequency and magnitude of signals measured is then fed down to the ground via a fibre-optic cable, where it is stored and subsequently analysed. In addition to the signal data, we also use GPS to monitor the balloon’s position, and a barometric altimeter to provide height information in real time.
By knowing the signal strength at a given location with a high level of certainty, aviation stakeholders will be in a far better position to assess the impact of a proposed wind turbine, and developers will have greater visibility of the constraining factors. Because measurement is better than prediction, we firmly believe that this approach will help all stakeholders understand the issues, and work together to find mutually acceptable solutions.
Aerostat Surveys
www.aerostat.co.uk
52
www.windenergynetwork.co.uk
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