N141-003 TITLE: Innovative Signal Processing Techniques for Mitigation of Wind Turbine Farm Interference in Airborne Radar Systems

TECHNOLOGY AREAS: Air Platform, Electronics, Battlespace

ACQUISITION PROGRAM: PMA 265

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted". The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Develop innovative signal processing techniques for the mitigation of adverse effects on airborne radar systems resulting from the interference caused by the large radar cross section of a wind turbine combined with the Doppler frequency shift produced by its rotating blades which impacts the ability of a radar system to differentiate a wind turbine from an aircraft.

DESCRIPTION: There is growing public and private sector interest in generating electrical power using wind energy both within the United States and abroad. Systems that harness wind energy are largely comprised of installations of multiple wind turbines with rotating blades reaching to heights of 500 feet. The quantity, height and rotation of wind turbines present technical challenges to the effectiveness of airborne radar systems. Wind turbine farms located within line of sight of an airborne radar system have the potential to degrade the ability of that radar to perform its intended function. The magnitude of the impact will depend upon the quantity, size, structural properties and location of the wind turbines. The physical size of the wind turbine blades results in a substantial radar cross section (RCS) target, irrespective of whether the blades are viewed face on or edge on by the radar. The tip velocities for wind turbine blades fall within a speed range applicable to aircraft and in fact the broadly spread variable Doppler signature of the reflected signal from the wind turbine can often exceed that produced by an aircraft. Consequently, the turbine blades will appear on a radar system as a moving target of significant size if they are within the radar line of sight. Responses cannot be inhibited using normal moving target indicator (MTI) based techniques since they are generated by a moving structure of long airfoils resulting in an extremely complex spectrum of Doppler returns.

Wind turbines in close proximity to military training, testing, and development sites and ranges can adversely impact the ability to test airborne radar systems and train Navy aviators in the proper operation of airborne radar systems. Since airborne radar systems are required to work independently, some of the traditional mitigation techniques used in a ground based scenario such as gap filling, wind turbine structural regulation, radio frequency (RF) signature reduction, and environmental techniques cannot be employed. In order to ensure that airborne radar systems can continue to function properly in an environment where wind turbine farm activity will continue to proliferate there is a need to develop an innovative signal processing technique within the radar system to mitigate the problems caused by wind farms.

PHASE I: Identify and define the RF signature from wind turbines in various configurations. Perform modeling and simulation of the RF returns from wind turbine farms, and investigate signal processing techniques for mitigation of wind turbine farm effects.

PHASE II: Develop, test, and demonstrate signal processing algorithms for mitigation of wind turbine farm effects with simulated wind turbine farm data, and several sets of radar data.

PHASE III: Complete testing of the wind turbine farm mitigation signal processing algorithm and transition the technology to appropriate platforms.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: There is a high potential for private sector use of algorithms developed under this topic. Primary
candidates for dual use of wind turbine farm mitigation technology are air traffic control and weather radar systems that must contend with the issue of interference resulting from the presence of wind turbines.

REFERENCES:
1. Air Warfare Centre Royal Air Force (2005). Further Evidence of the Effects of Wind Turbine Farms on AD Radar. London, UK. http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA466373

2. Jackson, C. A. Windfarm Characteristics and Their Effect on Radar Systems. http://www.jacksonresidence.pwp.blueyonder.co.uk/Radar2007_Windfarm_Characteristics_and_their_effect_on_radar.pdf

3. Jackson, C. A., & Butler, M. M. Options for Mitigation of the Effects of Windfarms on Radar Systems. http://www.jacksonresidence.pwp.blueyonder.co.uk/Radar2007_OPTIONS%20FOR%20MITIGATION%20OF%20THE%20EFFECTS%20OF%20WINDFARMS%20ON%20RADAR%20SYTEMS.pdf

4. Air Warfare Centre Royal Air Force. (2005). The Effects of Wind Turbine Farms on Air Defence Radars. London, UK. http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA467441

5. Air Warfare Centre Royal Air Force. (2005). The Effects of Wind Turbine Farms on ATC Radar. London, UK. http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA466350

6. Office of the Director of Defense Research and Engineering (2006). The Effect of Windmill Farms on Military Readiness: Report to the Congressional Defense Committees. http://www.defense.gov/pubs/pdfs/WindFarmReport.pdf

KEYWORDS: Radar, signal processing, wind turbines, clutter, RF, RCS target

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