Improved capabilities for siting wind farms and mitigating impacts on RADAR observations

The development of efficient wind energy production involves challenges in technology and interoperability with other systems critical to the national mission. Wind turbines impact radar measurements as a result of their large reflectivity cross section as well as though the Doppler phase shift of their rotating blades. Wind farms can interfere with operational radar in multiple contexts, with degradation impacts on: weather detection such as tornado location, wind shear, and precipitation monitoring; tracking of airplanes where air traffic control software can lose the tracks of aircraft; and in identification of other low flying targets where a wind farm located close to a border might create a dead zone for detecting intruding objects. As a result, a number of potential wind power locations have been contested on the basis of radar line of site. Radar line of site is commonly assessed using a standard atmosphere assumption; however, it has been shown that the index of refraction and refractive gradient may depart substantially from these conditions, especially in critical weather conditions. Moreover, as wind energy development looks to offshore locations where super-refractive conditions are common, the development of site specific radar line of site determination is necessary to provide the optimal balance between future energy development and radar requirements. In order to help meet the recent goal established for increasing the capability for 20% wind energy by the year 2030 (US DOE 2008), a climatology of radar line of site is provided to investigate site dependent deviation from standard atmosphere assumptions. Based on the climatology, specific conditions leading to negative impacts can be determined. Operational determination of radar beam propagation effects for real-time assessment of mitigation strategies as well as assimilation and synthesis of Radar data will be provided. Many current mitigation strategies are based on post-processing software to remove artifacts and to employ anomalous propagation filtering and correction methods. Providing predictive propagation fields would allow radar systems as well as processing systems to adaptively apply mitigation strategies in a more efficient manner. In the extreme case where exclusion zones are employed, these periods could be determined in advance such that their automated use would be minimized. Novel methods which employ radar data themselves to detect atmospheric refractivity profiles will be discussed. There are currently a number of wind farms that are within line of site of existing NOAA Doppler weather radars. These wind farms are situated at a range of distances, and therefore will provide quantitative evaluation of impact forecasts.