The suitable parameters to assess noise impact of a wind farm in a complex terrain: a case-study in Tuscan hills Luca Fredianelli E. Fermi Physics Department, University of Pisa, Pisa, Italy. Paolo Gallo Department of Pisa, Environmental Protection Agency of Tuscany Region, Pisa, Italy. Gaetano Licitra Department of Lucca, Environmental Protection Agency of Tuscany Region, Lucca, Italy. Diego Palazzuoli Technical Directorate, Environmental Protection Agency of Tuscany Region, Firenze, Italy. Summary Noise impact may represent a major hindrance to new wind farms. In Italy installations are usually planned in hilly areas, where amenity and quietness are the main attractiveness and characteristics. Moreover, in those scenarios, the influence of wind profiles on noise propagation is very complex due to the topography of the sites. Due to this peculiarity, the evaluation of noise impact of a wind farm is a tricky and weighty task. Specific instrumental investigations were performed in a wind farms in the Tuscan hills chosen as cases of study to analyze the critical aspects and to develop measurement and experimental procedures for a correct assessment of noise impact in a context of this type. 1. Introduction The noise impact of wind turbines is becoming a steady concern to the diffusion of large wind installations. The noise level from a wind farm may be quite low but differs from noise emitted by other sources in terms of generation, propagation and perception by neighbors. Everything about it is particular, therefore specialized techniques for measurements and data analysis are necessary to rationally assess impacts from existing and new operational projects. In contrast to other European countries, in Italy there is no specific legislation relating to wind turbine noise measurement and the limits set by existing rules [1], are not functional to control the annoyance of a wind farm. After a brief presentation of the methodologies in force in Italy for assessing the noise impact of conventional sources (like industrial sites), this document highlights the issues relating to the application of these methodologies to multi-turbine wind farms located in complex terrain. The aim is to propose useful parameters for the elaboration of a procedure to monitoring noise impact of operating wind farms and to compare the results with limit values for noise levels in force in Italy. The results obtained are based on the analysis and processing of noise data, wind speed at hub height, wind speed at receptor height and operational settings of the wind turbines that were acquired during a series of long term measurements performed near the wind farm "La Miniera" in the municipality of Montecatini Val di Cecina (PI). 2. Italian legislation on environmental noise In Italy there is no specific regulation for noise produced by wind farms, thus it is necessary to refer to more general standards on noise impact. Absolute limits for outdoor noise levels are related to six different classes of land use [2] whereas the indoor levels have to be compared to differential limit values for the immission (differential criterion). A ministerial decree [3] defines the detection techniques to be adopted for noise levels measurements, sets out as noise descriptor the equivalent A-weighted sound level (L Aeq ), calcutated on daytime (6:00 to 22:00) or nighttime (22:00 to 6:00). It also assigns the correction factors for tonal, low frequency or impulsive components. According to Italian law, therefore, the assessment of wind turbine noise must be done by treating the source as an industrial site: outdoor measurements at the receptor must be performed at least at 1 m of 783