By Jesse Lewis and Helen Lewis
Aircraft Detection Lighting Systems (ADLS) originated out of the “dark sky” initiative started in the 1950s by astronomers, who were concerned that nocturnal skyglow was obscuring stars. In 1988, the International Dark-Sky Association (IDA) was formed to reduce inappropriate or excessive use of artificial light. Wind farms, high voltage transmission lines, and communication towers in remote areas were particularly targeted. Most of us refer to this phenomenon as “light pollution”, affecting not only our ability to clearly see stars in the night sky, but also the natural behavior of animals - especially migrating birds.
In 2011, the FAA Obstruction Evaluation Services started research into radar-activated obstruction lighting technologies. They developed standards that resulted in AC70/7460-1L as Chapter 14: “Aircraft Detection Lighting Systems”. The FAA Technical Note states that, “Due to the number of existing telecommunication towers and wind turbines, combined with expected future construction, the number of obstructions that have these required lighting fixtures has greatly increased. The light generated by the increased number of fixtures has created a light pollution nuisance to residents living near these obstructions. Using an ADLS could have a positive impact on this problem by limiting the amount of time light fixtures are active while still providing a sufficient level of safety for pilots operating at night in the vicinity of these obstructions.”
ADLS radar monitors the airspace around the windfarm for aircraft. When aircraft cross a pre-set perimeter, the system signals the wind farm network to turn the lights ON. When the aircraft exits the control perimeter, the system issues a “lights OFF” signal. The objective is to have the lights OFF as much as possible. Many rural areas have limited aviation at night, and so enjoy lights off the majority of the time.
The FAA has designated that the radar should be able to detect the aircraft a minimum of 3 NM (5.5 km) – horizontally - away from the obstruction or perimeter of a group of obstructions. It should also provide vertical detection coverage from the ground up to 1,000 feet (304 m) above the highest part of the obstruction or group of obstructions, for all areas within the 3 NM (5.5km) zone. It must be noted that not all wind farms are on flat plains. Some are in mountainous areas, which is why the “highest part” of the obstruction(s) is crucial. The 1000-foot limit eliminates the lights coming on and off due to commercial air traffic; depending on the location, these aircraft will be flying far above the obstruction. The FAA does, however, reserve the right to prohibit the use of ADLS, modify or adjust the lighting plan, and have input on the sensor's location. This typically applies in areas close to airports, low level flying routes, near DoD facilities, and where frequent low-level flights occur.
Safety is the most important aspect of an ADLS. The operational default is lights ON, until every criterion is met and approved by the system to turn the lights OFF. The ADLS system has a heartbeat; if there is a loss of communication by any device, the lights will default to ON until all system components are back online. To ensure the radar system is always optimized, the system is monitored remotely 24/7, 365 days a year.
The radar is generally placed on the ground, but can be placed on top of a transmission tower - wherever it can get a clear line of sight (radar is not X-ray, and can be blocked by solid objects like buildings and mountains). Radar sends out a pulse of energy and measures the time it takes to reflect from a target and return to the radar antenna. The time it takes the pulse to reach the target provides the range. Distance to the target is one-half the time of the round trip. Detailed GIS studies and modeling are done of the area to create viewshed maps, which give the ADLS provider and the customer the best information on where to site the radar.
Compared to placing a radar on a high tower, installation costs are lower for ground-based systems. Ground-based skid systems also offer lower cost O&M compared to placing the system on a tall tower, which requires a certified climber. In some cases, a ground-based system isn’t feasible due to insufficient radar coverage, and a tower system is unavoidable. Once the location for the radar has been selected, the system is placed and anchored to a concrete pad. Power and fiber are connected to the cabinet/radar unit (for remotely located equipment). The commissioning phase involves 7-14 days of radar operation to ensure the system is optimized. The main issues with optimizing radars are the removal of false positives in the radar signal (birds, vehicles, clutter, etc.). After commissioning, flight tests are done to confirm the system is functioning optimally and in compliance with FAA requirements. When commissioning and testing are complete, the ADLS can go live. Once operational, the only onsite work will be a yearly inspection of all components, and a site visit by a technician. Almost all issues can be resolved via remote connection; on-site and remote staff can be trained to monitor the system. The ADLS SQL data system compiles and stores all data while the system is operating. The FAA requires a minimum of 15 days of data storage. Daily reports are sent to the client and to Government regulating bodies, as required.
ADLS monitoring can help wind farm operators meet all necessary requirements regarding light pollution. From siting through to operation, it’s a comprehensive approach to ensuring safe delivery of clean energy (for both people and animals).
Jesse Lewis is General Manager for DeTect Americas, and Helen Lewis is Marketing Coordinator for DeTect, which specializes in advanced radar and other sensor technologies, including bird radar technologies for real-time aircraft bird strike avoidance, wind energy bird mortality risk assessment and mitigation, and industrial bird control.
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