Wind Turbines and Air Traffic Contol
Throughout the world, wind turbines are rapidly becoming a widespread feature of landscapes, because of efforts to reduce dependence on fossil fuels, spurred on by presidential mandates and global agreements. Air traffic control radars are just one of many types of radar that are being directly affected by the proliferation of wind turbines in the environment, and Raytheon is one of the leading companies addressing the issue of wind turbine and radar coexistence.
By Peter Drake, Raytheon Company, USA, and Brian Smith, Raytheon Canada Ltd
Wind Turbine Siting Guidelines
Eurocontrol has released draft guidelines to air navigation service providers (ANSPs) to aid in the assessment and mitigation of wind farm effects on airspace surveillance systems. The draft guidelines were developed in close collaboration with civil and military surveillance system providers from across Europe, as well as with input from air navigation authorities in Australia, Canada, Japan, New Zealand and the USA. As the document states:
Unless sited with care, wind turbines can have a detrimental impact upon many aspects of aviation.
and
Such aspects include, but are not limited to, performance reduction of ATM infrastructure (communication, navigation and surveillance), constraints on procedure design, airspace planning and design, minimum safe altitudes, climb rates of aircraft, descent rates of aircraft, procedures to ensure that wind turbine locations are correctly represented on maps and in terrain avoidance tools (and) procedures to ensure that they are appropriately lit, etc
The proposed process set out in the guidelines defines four different geographical zones, based on simple criteria, for each type of sensor (confined to primary and secondary radar for the time being). In the ‘safeguarding’ zone, the closest area to the sensor, wind turbines are not allowed to be built. In the second zone, wind turbines can be built provided that a complex and detailed impact assessment analysis demonstrates that the impact can be tolerated. In the third zone, wind turbines can be built on the basis of the results of a simple impact assessment analysis. In the last zone, wind turbines can be built without any constraints.
In general, a large percentage of wind farm developments generate objections because of potential ATC or air defence issues. The British Wind Energy Association (BWEA) estimates that 4.7GW of renewable energy projects are being held up because of military or civil aviation concerns, while in the USA the American Wind Energy Association (AWEA) estimates that over 9GW of renewable energy projects are being held up for similar reasons. This is expected to grow exponentially as the wind energy roll-out gets into full swing, reflecting the 45% increase in US wind energy projects between 2009 and 2010.
Typical ATC Radar Impacts
Smaller wind farms generally present fewer problems, but the need to find a solution has become more pressing as applications for larger and larger wind farms, including those offshore, are put forward. However, turbines of any size or configuration can create a false target or false weather effect. Figure 2 (courtesy Volpe) depicts typical effects such as loss of primary targets (red), false targets (blue), and fully tracked targets (green) at Travis Air Force Base (AFB) prior to applying mitigation techniques. Note that there is a significant section above the wind resource area where primary target detection is lost.
Mitigation Techniques and Capabilities
Being one of the pre-eminent suppliers of air traffic management (ATM) equipment globally, Raytheon has been applying its radar and signal data processing expertise to develop and implement solutions supporting wind turbine and radar coexistence, thus allowing wind turbines to be sited closer to radar facilities. The company has engaged both government agencies and the global wind energy industry in advancing solutions so that they can be certified for operation in the air traffic domain. Experience has shown that there is no single silver bullet, and therefore Raytheon is providing a suite of enhancements that can be adapted to the specific operational environment. These enhancements distinguish the radar returns from wind turbines from those of aircraft, removing the former from the processed signal.
The current and future enhanced set of mitigation techniques are outlined in Table 1 that are available depending on ATM radar configuration. The ‘ASR-XX’ flag indicates that the corresponding technique can be applied to all Raytheon ATM radars, while the ‘ASR-11’ flag indicates that the technique is only currently available on the US configuration. Those techniques flagged with ‘LRR’ are available on the upgraded US Long Range Radars.
Table 1. Suite of mitigation techniques
Application of the ‘implemented’ techniques to the ASR-11 at Travis AFB, along with optimisation and improved tracking capabilities, has proved that application of a subset of the suite resulted in regained detection. As depicted in Figure 3, this significant improvement in radar capability allowed base operations to proceed, and wind turbines and radar to coexist. This occurred as a result of cooperation in the USA between local authorities, the base, and the wind energy suppliers.
Raytheon is under contract to UK NATS to implement the mitigation techniques that are depicted as being ‘under development’ in Table 1. Raytheon has been working with UK NATS on wind turbine mitigation since 2005, when NATS approached Raytheon Canada. The company later carried out an initial study for NATS, which ultimately led to the current project.
The company laid out a careful schedule with NATS, BWEA and the UK DECC (Department of Energy and Climate Change), and with funding now in place expects it to take around two years from the start of the contract to do the final development and test for NATS.
The cost of the £5 million (US$ 8.3 million) project has been picked up by the BWEA, DECC, Crown Estates and other private wind energy providers in the UK. The backbone processor required for this project, otherwise known as the Advanced Signal Data Processor, was developed cooperatively between Raytheon, the US Federal Aviation Administration (FAA) and the Department of Defense (DoD).
The solution set comprises a suite of signal processing enhancements, combined with an enhanced tracking capability. Sophisticated signal processing and tracking algorithms will be applied at the radar to eliminate the wind turbine blades as a false target. Raytheon’s approach does not suppress returns from real targets and therefore enables the operator to clearly identify real targets. This approach differs from other solutions that attempt to remove the turbine radar clutter using downstream processing.
After field testing in 2010, Raytheon claims it will have the first radar set-up with an integrated suite of solutions that will successfully allow wind turbine and radar coexistence.The company is planning on two field tests with NATS – one relates to en route radars and the other for terminal area coverage, because both can experience the problem. The locations for these trials are the en route site at Lowther Hill in the UK, and the terminal site at Soesterberg in the Netherlands.
Future Gap Fill Radar
Raytheon is also developing a stand-alone low-cost x-band phased array gap filler radar solution that will be capable of both target and weather detection, and will use advanced processing techniques similar to those available with the ATM radars. The gap filler radar is designed so that it can be integrated with wind farms, and will allow data to be merged with that of other radars. The first production prototype of this radar will be under test in 2011.
Summary
Raytheon believes that there is currently no low cost silver bullet to wind turbine and radar coexistence, and as such is developing a cost-effective suite of solutions for ATC and other radars. Upon successful completion of testing and evaluation, Raytheon will be the first company to offer an ATC radar solution that has a built-in system to effectively mitigate the radar returns from wind farms.
Biography of the Authors
Peter Drake is ATM Future Surveillance Lead and DASR Technical Director. He has over 30 years’ experience developing ATC Systems. Mr Drake holds a BSc with Honours in Electrical and Electronic Engineering from the University of Bath (UK). Mr Drake is a recipient of the prestigious Raytheon Thomas L Philips award.
Brian Smith is the General Manager at Raytheon Canada Limited, which specialises in solid-state air traffic control radar systems and services. Mr Smith holds a masters in business administration from Wilfred Laurier University, and a bachelor’s degree from the University of Waterloo in systems design engineering.{/access}
Throughout the world, wind turbines are rapidly becoming a widespread feature of landscapes, because of efforts to reduce dependence on fossil fuels, spurred on by presidential mandates and global agreements. Air traffic control radars are just one of many types of radar that are being directly affected by the proliferation of wind turbines in the environment, and Raytheon is one of the leading companies addressing the issue of wind turbine and radar coexistence.By Peter Drake, Raytheon Company, USA, and Brian Smith, Raytheon Canada Ltd
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}Wind turbines that are sited in the view of radars can cause blind spots for air traffic control (ATC); radar clutter that can result in the loss or corruption of a real aircraft’s position. This equivalent return can appear on a controller’s radar screen as a moving aircraft or, equally disconcerting, as strong false weather. In ATC circles this is described as a false target/false weather and may cause the air traffic controller to re-route aircraft. Thus these false targets create additional work for controllers, and may also have safety implications. Typical issues caused by turbines are circled in Figure 1 which shows (from left to right), false air traffic targets, radar clutter and false weather.
When a wind turbine is in operation, the spinning blades create a Doppler effect that appears on the radar to be equivalent to a Boeing 747 on final approach. The radio frequency energy coming from the radar is picked up by the turbine blades and returned to the radar as though it is a moving target. This problem can be partially offset by wind turbine siting.Wind Turbine Siting Guidelines
Eurocontrol has released draft guidelines to air navigation service providers (ANSPs) to aid in the assessment and mitigation of wind farm effects on airspace surveillance systems. The draft guidelines were developed in close collaboration with civil and military surveillance system providers from across Europe, as well as with input from air navigation authorities in Australia, Canada, Japan, New Zealand and the USA. As the document states:
Unless sited with care, wind turbines can have a detrimental impact upon many aspects of aviation.
and
Such aspects include, but are not limited to, performance reduction of ATM infrastructure (communication, navigation and surveillance), constraints on procedure design, airspace planning and design, minimum safe altitudes, climb rates of aircraft, descent rates of aircraft, procedures to ensure that wind turbine locations are correctly represented on maps and in terrain avoidance tools (and) procedures to ensure that they are appropriately lit, etc
The proposed process set out in the guidelines defines four different geographical zones, based on simple criteria, for each type of sensor (confined to primary and secondary radar for the time being). In the ‘safeguarding’ zone, the closest area to the sensor, wind turbines are not allowed to be built. In the second zone, wind turbines can be built provided that a complex and detailed impact assessment analysis demonstrates that the impact can be tolerated. In the third zone, wind turbines can be built on the basis of the results of a simple impact assessment analysis. In the last zone, wind turbines can be built without any constraints.
In general, a large percentage of wind farm developments generate objections because of potential ATC or air defence issues. The British Wind Energy Association (BWEA) estimates that 4.7GW of renewable energy projects are being held up because of military or civil aviation concerns, while in the USA the American Wind Energy Association (AWEA) estimates that over 9GW of renewable energy projects are being held up for similar reasons. This is expected to grow exponentially as the wind energy roll-out gets into full swing, reflecting the 45% increase in US wind energy projects between 2009 and 2010.
Typical ATC Radar Impacts
Smaller wind farms generally present fewer problems, but the need to find a solution has become more pressing as applications for larger and larger wind farms, including those offshore, are put forward. However, turbines of any size or configuration can create a false target or false weather effect. Figure 2 (courtesy Volpe) depicts typical effects such as loss of primary targets (red), false targets (blue), and fully tracked targets (green) at Travis Air Force Base (AFB) prior to applying mitigation techniques. Note that there is a significant section above the wind resource area where primary target detection is lost.
Mitigation Techniques and Capabilities
Being one of the pre-eminent suppliers of air traffic management (ATM) equipment globally, Raytheon has been applying its radar and signal data processing expertise to develop and implement solutions supporting wind turbine and radar coexistence, thus allowing wind turbines to be sited closer to radar facilities. The company has engaged both government agencies and the global wind energy industry in advancing solutions so that they can be certified for operation in the air traffic domain. Experience has shown that there is no single silver bullet, and therefore Raytheon is providing a suite of enhancements that can be adapted to the specific operational environment. These enhancements distinguish the radar returns from wind turbines from those of aircraft, removing the former from the processed signal.
The current and future enhanced set of mitigation techniques are outlined in Table 1 that are available depending on ATM radar configuration. The ‘ASR-XX’ flag indicates that the corresponding technique can be applied to all Raytheon ATM radars, while the ‘ASR-11’ flag indicates that the technique is only currently available on the US configuration. Those techniques flagged with ‘LRR’ are available on the upgraded US Long Range Radars.
| IMPLEMENTED – but result in reduced detection | ||
| Sensitivity Time Control (STC) | ASR-XX | LRR |
| Range Azimuth Gating (RAG) | ASR-XX | LRR |
| Track Initiation Inhibiting | ASR-XX | LRR |
| Velocity Editing | ASR-XX | LRR |
| Plot Amplitude Thresholding (PAT) | ASR-11 | LRR |
| UNDER DEVELOPMENT – Regains detection capability | ||
| Concurrent Beam Processing | ASR-XX | |
| Improved Constant False Alarm Rate (CFAR) | ASR-XX | LRR |
| Clutter Map per Doppler Filter | ASR-XX | LRR |
| Optimisation and Enhanced Tracking Techniques | ASR-11 | LRR |
| PROSPECTIVE – Extends capability | ||
| Polarimetrcs (Duel Polarisation) | ASR-XX | |
| Pulse-burst (High PRF) | ASR-XX | LRR |
| Blind Spot/Gap-Filler | ASR-XX | LRR |
Table 1. Suite of mitigation techniques
Application of the ‘implemented’ techniques to the ASR-11 at Travis AFB, along with optimisation and improved tracking capabilities, has proved that application of a subset of the suite resulted in regained detection. As depicted in Figure 3, this significant improvement in radar capability allowed base operations to proceed, and wind turbines and radar to coexist. This occurred as a result of cooperation in the USA between local authorities, the base, and the wind energy suppliers.
Raytheon is under contract to UK NATS to implement the mitigation techniques that are depicted as being ‘under development’ in Table 1. Raytheon has been working with UK NATS on wind turbine mitigation since 2005, when NATS approached Raytheon Canada. The company later carried out an initial study for NATS, which ultimately led to the current project.
The company laid out a careful schedule with NATS, BWEA and the UK DECC (Department of Energy and Climate Change), and with funding now in place expects it to take around two years from the start of the contract to do the final development and test for NATS.
The cost of the £5 million (US$ 8.3 million) project has been picked up by the BWEA, DECC, Crown Estates and other private wind energy providers in the UK. The backbone processor required for this project, otherwise known as the Advanced Signal Data Processor, was developed cooperatively between Raytheon, the US Federal Aviation Administration (FAA) and the Department of Defense (DoD).
The solution set comprises a suite of signal processing enhancements, combined with an enhanced tracking capability. Sophisticated signal processing and tracking algorithms will be applied at the radar to eliminate the wind turbine blades as a false target. Raytheon’s approach does not suppress returns from real targets and therefore enables the operator to clearly identify real targets. This approach differs from other solutions that attempt to remove the turbine radar clutter using downstream processing.
After field testing in 2010, Raytheon claims it will have the first radar set-up with an integrated suite of solutions that will successfully allow wind turbine and radar coexistence.The company is planning on two field tests with NATS – one relates to en route radars and the other for terminal area coverage, because both can experience the problem. The locations for these trials are the en route site at Lowther Hill in the UK, and the terminal site at Soesterberg in the Netherlands.
Future Gap Fill Radar
Raytheon is also developing a stand-alone low-cost x-band phased array gap filler radar solution that will be capable of both target and weather detection, and will use advanced processing techniques similar to those available with the ATM radars. The gap filler radar is designed so that it can be integrated with wind farms, and will allow data to be merged with that of other radars. The first production prototype of this radar will be under test in 2011.
Summary
Raytheon believes that there is currently no low cost silver bullet to wind turbine and radar coexistence, and as such is developing a cost-effective suite of solutions for ATC and other radars. Upon successful completion of testing and evaluation, Raytheon will be the first company to offer an ATC radar solution that has a built-in system to effectively mitigate the radar returns from wind farms.
Biography of the Authors
Peter Drake is ATM Future Surveillance Lead and DASR Technical Director. He has over 30 years’ experience developing ATC Systems. Mr Drake holds a BSc with Honours in Electrical and Electronic Engineering from the University of Bath (UK). Mr Drake is a recipient of the prestigious Raytheon Thomas L Philips award.
Brian Smith is the General Manager at Raytheon Canada Limited, which specialises in solid-state air traffic control radar systems and services. Mr Smith holds a masters in business administration from Wilfred Laurier University, and a bachelor’s degree from the University of Waterloo in systems design engineering.{/access}
