Federal Radar and Impact Zones

Different types of radar serve many purposes, including scanning the skies for planes and other objects, determining the speed of a car, finding obstructions and ships in the ocean, and tracking weather. Weather radar is used to locate precipitation, track its motion, and estimate its type (rain, sleet, snow, hail, etc.), severity, and amount. Weather radar with Doppler capability can also measure environmental wind speeds, detect dangerous wind shear near airports, and estimate the likelihood of a tornado. The useful range of federal weather radar is about 250 nautical miles. Weather radar stations are located all across the U.S., including the coastline. Building structures, including wind turbines, can impact operations of weather radar stations. So what do wind energy planners need to know about federal weather radar stations and their impact zones?

  1. The weather radar and radar impact zones are two separate layers. Within, weather radar stations and the respective impact zones have been separated into separate data layers. Both data sets cover the entire U.S.; however, the stations are merely points while the impact zones cover large areas around the radar.
  2. Impact zones were calculated to determine potential wind farm conflict. Two agencies manage federal weather radar. NOAA’s WSR-88D Radar Operations Center (ROC) manages 160 Next Generation Weather Radars (NEXRADs), officially designated as Weather Surveillance Radar 1988-Doppler (WSR-88D). The Federal Aviation Administration (FAA) manages 45 Terminal Doppler Weather Radars (TDWRs), with a specific mission to detect low-level wind shear and other severe weather near major airports. The ROC created impact zones for each of the 160 NEXRAD/WSR-88D radars (note: some of the overseas WSR-88Ds are not included in the Marine Cadastre data). Using a maximum wind turbine blade-tip height of 160 meters for calculations, the ROC created four areas surrounding each station with corresponding red, brown, yellow, and green colors. Red signifies a “No Build Zone” where wind turbines are certain to cause significant impacts to radar returns and forecast operations. Orange represents the “Mitigation Zone” where significant operational impacts are likely and adjustments to the project or other mitigation efforts would be requested. Yellow represents the “Consultation Zone” where significant operational impacts are possible, depending on the height and number of wind turbines, and distance from the radar. Green represents the “Notification Zone” where the wind farm would occasionally be visible in the radar data but where significant impacts are not likely. NOAA would like to be notified by wind farm developers about the project so that radar users are not surprised by the wind turbine clutter.
  3. There are two types of possible interaction. The first type of interaction creates interference with the radar to give the illusion that something is there that really isn’t. For example, wind turbines that are in the radar’s line of sight could cause the radar scan to show a storm in an area where there is no precipitation at all. The radar’s automated precipitation algorithms, in turn, accumulate rainfall where there is none. The other type of interaction hides things that should show up on the radar scan. For example, a large storm cell might be covering a coastal city, but the wind turbines hide part of the storm. Although research is ongoing, there are currently no known radar signal processing techniques that can adequately filter out wind turbine clutter while retaining the weather signal. Therefore, wind energy developers should consider the potential impacts to federal weather radar when planning their projects.

Quick Caveats. The NEXRAD/WSR-88D impact zones were calculated using a specific height of 160 meters, which is only slightly higher than the typical terrestrial wind turbine. There is the potential for these zones to change for offshore turbines if the typical turbine height becomes significantly greater the 160 meters. The FAA and NOAA radars have significantly different missions. The FAA has not calculated impact zones for the TDWR, but any turbines within the radar’s mission area, which is defined by a 60-nautical-mile radius circle around the TDWR, would need to be evaluated for impacts by the FAA. Planners should consider the effects on TDWR radar stations when considering a project within 60 nautical miles of a TDWR. The Department of Defense (DoD) has placed its DoD preliminary screening tool on the FAA’s Obstruction Evaluation website to help developers quickly and anonymously determine if there might be negative interactions between a proposed wind farm and the NEXRAD / WSR-88D weather radar, DoD Homeland Defense radar, or military operating areas.

Data-Source Experts
Ed Ciardi, NOAA Radar Operations Center;

For questions, please contact