Understanding the components of site aviation assessment process

Large on and offshore wind farm developments are beginning to proliferate and these projects can have a big impact on the operations of the aviation industry.

In this context, it is critcal to be equipped with the relevant information about the concerned authorities and what can result as obscructions in the progress of the respective parties involved.

Aviation stakeholders typically fall into one of two categories, according to Clive Jackson, Lead Consultant, Wind Farm Technology, BAE Systems. These two categories are: Civil (National or Airfield) Air Traffic Services  providers (e.g. in the UK NATS and Europe EUROCONTROL or individual airports) or Military (Military Air Traffic Control or Air Defence operations).

Objections from these stakeholders can fall into a number of categories, said Jackson, who is scheduled to speak during European Wind Farm Site Selection Summit to be held on 1-2 April in Hamburg . These include:

·          Impact on radar - Wind farms have a well documented impact on radar performance, most aviation stakeholders rely on radar to provide aircraft position information either for safety of life purposes or air defence purposes.

·          Low Flying or Physical Aviation Obstuction: In some cases turbines may be so tall that they would cause a hazard to low flying aircraft and thus prevent aircraft from safely landing or carrying out low level training exercises

·          Cumulative impact: In some cases, where an Aviation Stakeholder may be able to manage the effects of a small number of wind turbines operationally, they will still object on the basis of a cumulative impact of many turbines or wind farms in their area.
There may also be some issues with Instrument Approach Procedures at some airports, while Meterological service providers may also object on the basis of impact on weather radar, which may be providing information to Aviation Stakeholders for flight planning purposes.

"These issues are quite specific to each stakeholder and need to be understood early in the planning (or pre-planning) process to determine how critical they are. It is possible to predict the impact on aviation of a given wind farm provided certain information is made available such as site location, layout and turbine sizes. With our in depth aviation and radar expertise, this is part of the service that we at BAE Systems are able to offer. As part of our site assessments we are able to give an indication of any mitigation options that may be available to resolve any objections," Jackson told windenergyupdate.com.

Evaluating the potential effect of a wind farm on radar early in the planning process

Jackson says the first step is to determine if a wind farm would even be visible to any radars. This can be achieved using radar propagation modelling tools using a terrain database. These work in a similar way to Visual Impact prediction tools currently used by wind farm developers - except the radar tools require details of radar performance and take into account a variety of radio propagation effects not relevant to optical propagation such as refraction and diffraction over terrain.

The sort of factors that influence wind farm visibility include site location, turbine layout, turbine size, radar location and intervening terrain. 

"However, the most important factor is the radar reflectivity of wind turbines. This is called 'Radar Cross Section' (RCS) and, depending on orientation with respect to a radar, wind turbines can have RCS many thousands of times larger than aircraft. It is this factor which determines to a large extent how visible and how much impact a wind turbine will have on a radar," pointed out Jackson.

Once it is determined that a wind farm would be visible to a given radar, an analysis of the performance impact must be undertaken, based on an understanding of how the radar is designed and operated. Typically effects fall into three categories:

·          Unwanted turbine reports on the radar displays. This 'Clutter' can be a source of distraction or may obscure wanted aircraft reports.

·          Reduced probability of detecting the wanted aircraft reports in the vicinity of turbines.

·          Tracking performance degradation - where there are radar reports of lots of turbines (that look like aircraft) and not many genuine aircraft reports then the probability of automatic aircraft tracking systems maintaining a good quality track on only the  genuine aircraft is much reduced.  This can result in an effect called 'Track Seduction' where an aircraft appears to be flying around in circles within a wind farm, when in fact it has flown away somewhere else!

"In some cases these performance impacts, while seeming bad at first glance, may not actually have an operational impact on the Aviation Stakeholder (for example if the wind farm is in an area that is not of operational significance to the stakeholder). However, in many cases these impacts on the radar result in an unacceptable impact on the stakeholders ability to carry out their operations safely or effectively," said Jackson. 

This performance and operational analysis is something which BAE Systems undertakes with every wind farm developer  and project it deals with.

"This allows us, if necessary to then liase with the Aviation Stakeholder(s) with a good understanding of their potential issues and also how they might be mitigated," said Jackson.

In terms of demonstrating the impact, as a result of research and published reports over the past few years, many stakeholders are aware of the impact on other radar systems of existing wind farms. In some cases these impacts are not as relevant to a specific stakeholder and it is vitally important to engage with them as early as possible after identifying them to understand their concerns and investigate a way forward.

"Here at BAE Systems we are using our operational experience to allow us to engage with aviation stakeholders on the same terms and in a language we both understand to explain impacts and discuss mitigation options," said Jackson.

European Wind Farm Site Selection Summit

BAE Systems' Clive Jackson is scheduled to speak during European Wind Farm Site Selection Summit, which is scheduled to take place on 1-2 April in Hamburg this year.

For more information click here: http://www.windenergyupdate.com/eurosite09/programme.shtml

or contact: Ian Evans by email ian@eyeforenergy.com