Radar signals and wind turbines are, in a sense, natural enemies. Military radar installations are generally located such that their coverage above the surrounding terrain is as unobstructed as possible. Wind turbines are generally located on the top of hills or ridges and made as tall as possible.
The most relevant categories of military radar as they pertain to wind development are set out below. However, in general terms, the potential for interference stems from the fact that all radar systems emit an electromagnetic pulse, which interacts with a target of interest, and the returning signal is analysed to provide information about the target. Wind turbines, like any other physical structure, have the potential to interact with the radar signals to varying degrees, and this can affect the quality of the returning signal and, consequently, degrade the quality of the information.
This article focusses on military radar constraints. An article focussing on civil radar constraints can be found here.
Stakeholders
Common parties that safeguard military radar infrastrucure are listed below, however this is not an exhaustive list:
- Government bodies, including ministeries and other departments that are dedicated to a country’s air force or defence interests in general.
- Military air bases themselves, if their safeguarding is more autonomous.
- Military aviation authorities, which typically have a regulatory role, not a direct safeguarding duty.
Radar Types
Military radar can be:
- Non-cooperative (primary radar), which is to say designed to detect targets based on their physical presence only.
- Co-operative (secondary radar), which means in communication with a transponder on-board a friendly aircraft.
Mitigation
Radar mitigation is a very broad and dense subject in its own right, this is not covered in depth here. However, an overview of the extent to which mitigation is typically available will be given for context purposes. With this in mind, it is important that we distinguish between two categories of mitigation:
- Technical mitigation – by which something is there is some change made to the hardware and/or software associated with the radar system and/or the turbines themselves. This could include the incorporation of in-fill coverage from an alternative radar, or the application of a stealth coating to a turbine blade, for example.
- Operational mitigation, whereby the impact is tolerated as being acceptable. It is often subject to marking the turbines’ presence on associated charts and other published information or changing specific flight procedures and airspace.
Military Radar: Air Traffic Control
Military air bases often have radar installations for managing air traffic approaching and departing the base. Such radar can be primary and/or secondary as set out above.
Primary radar can be adversely affected by wind turbines because the reflections from the moving blades can be processed as reflections from aircraft, leading to a target being shown on a radar screen. Technical and operational mitigation are both, in principle, options for developers facing potential impacts in this regard. The available options depend on the level of impact, the budget for mitigation and the quality of the relationship between the developer and the stakeholder (among other factors).
Secondary radar can also be affected by wind turbines because signals between the radar and the aircraft can be affected by the presence of the turbines. Mitigation options are, in general terms, more restricted here. However, the likelihood of an impact is generally less for secondary than for primary radar, all things being equal.
Impacts on military air traffic control radar can stop projects going ahead, but it’s an area where advances have been made in recent years.
Military Radar: Air Defence
Military air defence radar are typically long-range radar installations that are strategically located to detect hostile jets. In the case of the UK for example, air defence radar installations are mainly located on the east coast of the country.
Some air defence radar are more sophisticated than others. Some models purport to have more options for mitigating turbine impacts specifically.
Technical mitigation solutions do exist for air defence radar, however there are fewer viable options than there are for regular air traffic control primary radar. In addition, air defence radar installations are usually safeguarded more robustly than air traffic control radar.
Impacts on air defence radar are not an automatic showstopper for wind developments, but they can present a very significant constraint.
Military Radar: Precision Approach Radar
Precision approach radar installations are specifically designed to guide an aircraft in to land, maximising safety even in poor visibility. They are exclusively used by military air bases. The good news is that relatively few aerodromes have precision approach radar, and they are typically only safeguarded in a relatively small area (e.g. a cone extending to 20 nautical miles off the end of the runway, with exceptions). The bad news is that technical mitigation options effectively don’t exist, and operational acceptance is highly unlikely (although not entirely unprecedented).
The safeguarded areas associated with precision approach radar can be treated as de-facto exclusion zones from an onshore development perspective.
Figure 1 below summarises the main military radar constraints for onshore wind development.
Figure 1 – Summary of main military constraints (onshore wind)
Other Constraints
Military interests can utilise other types of radar and navigation infrastructure that can be affected by wind developments. The types listed above comprise the majority of constraints to onshore wind.
Pager Power
Pager Power has over 20 years of experience in modelling impacts of onshore wind turbines on surrounding infrastructure and engaging military stakeholders in order to progress development. If we can help you with your project, please do get in touch.
Thumbnail image accrediation: David Vives (November 2017) on Unsplash.com. Last accessed on 8th October 2024. Available at: https://unsplash.com/photos/a-row-of-wind-turbines-on-a-hill-JDD2cvwM4m4