Potential impacts from operational noise produced by wind turbines is a major issue during the project planning and permitting process, particularly for projects east of the Mississippi River in fairly populous areas. While still an issue farther west, more buffer space and lower population densities sometimes make noise less of a factor. In general, however, noise may be the principal obstacle, from an environmental impact standpoint, to the more rapid growth of this renewable energy source in the United States. Proposed projects are frequently opposed on noise concerns, if not outright fear, usually aroused by the highly biased misinformation found on numerous anti-wind websites. While significant noise problems have certainly been experienced at some newly operational projects, they are usually attributable to poor design (siting units too close to houses without any real awareness of the likely impact) or to unexpected mechanical noises, such as chattering yaw brakes or noisy ventilation fans. A common theme at sites with legitimate complaints is that no one-not the developer, their consultants or the regulatory authority-really understood the import and meaning of the sound levels predicted at adjacent homes in project environmental impact statement (EIS) noise modeling. This paper seeks to address this lack of knowledge with suggested design goals and regulatory limits for new wind projects based on experience with the design of nearly 60 large wind projects and field testing at a number of completed installations where the apparent reaction of the community can be compared to model predictions and measurements at complainant's homes.

There is a need in the United States for some Federal or prominent standards organization to publish limits in residential areas for low frequency noise attributable to industrial sources. This paper proposes maximum limits based on experience in investigating and solving low frequency noise problems, principally from open cycle combustion turbine installations The author believes the recommended C-weighted limits in this paper are applicable to most common steady low-frequency noise sources in addition to combustion turbines due to the combined tonal and broadband character of the sound. It is hoped standardizing bodies can add this reference to the larger body of literature to arrive at a workable sorely-needed standard.

Excessive low-frequency noise from open-cycle combustion turbine power plants has been recognized as a serious noise and vibration problem since the early 1970s. Yet, the problem still occurs, mainly because siting and specifying agencies are largely uninformed about the problem and because there are no standardized noise criteria in the U.S. to consult for guidance in avoiding low-frequency noise problems. Detailed sound pressure level measurements from five low-frequency problem sites are analyzed for support of a proposed criterion. The data are compared to noise and vibration thresholds. In addition, a small sampling of responses from residents to varied levels of low-frequency noise immissions is presented. This paper proposes a "C" weighted overall sound level criterion. The proposed criterion should be applicable to most industrial sources of steady low-frequency noise in addition to combustion turbines.

Despite the use of windscreens, the measurement of ambient sound levels or noise emissions in quiet environments can be adversely affected by wind blowing over the microphone. This is especially true when environmental impact assessments are being carried out for proposed wind turbine power projects where the objective is to determine the level of background masking noise available as a function of wind speed, since any potential noise impact from the project will only occur under moderately windy conditions. Under calm conditions the project will produce no noise at all. A number of windscreen products are commercially available for short and long-term sound level monitoring in adverse weather conditions. Generally, these windscreens vary by physical size and the method of preventing water from reaching the microphone. High frequency attenuation effects are usually available from the product suppliers but, in general, low frequency turbulence effects are not available. Consequently, a controlled laboratory test program was carried out in a state-of-the-art wind tunnel at the Fraunhofer Institut fur Bauphysik in Stuttgart, Germany to quantify the level of low frequency interference (down to 6.3 Hz) associated with a number of different foam windscreens and an aerodynamic microphone nose cone. A total of nine configurations were tested with "quiet" airflow only, artificial noise only and noise plus airflow to evaluate both low frequency wind induced noise and high frequency attenuation effects. The test program demonstrated that the largest size foam-based windscreens provided the most protection from flow induced noise due to wind. Flow induced noise by air flow alone was estimated from the study results and compared to community noise measurements at a typical wind turbine site. It was determined that flow induced wind noise does not have a significant or detrimental effect on the measurement of A-weighted sound levels under wind conditions of concern as long as the suggested measurement techniques described herein are followed

For interpretation ofthermally driven mesoscale circulation systems, meteorologists are interested in detailed structures of boundary-layer temperature fields. The surface temperature of a coastal region is analyzed using an optimum interpolation scheme. Covariance estimates are frequently based on the assumption of isotropy. The interpolation is improved by consideration of the anisotropic character induced by inhomogenities ofthe terrain. By a simple model, typical variations of the covariance function in a coastal zone are estimated. The results are discussed by a comparison of interpolated and observed time series. Finally the refined statistical model is tested by the application to objective analysis of coastal surface temperature fields. It is evident that the specification of topographic dependencies leads to a reduction of mean square interpolation error.