In the last decade limits on environmental noise have been established by legislation in many European countries. Usually these limits have different values for day and night period and, often, depend also on the land use (noise zoning). To checkthat the limits are not exceeded, the L{sub}(Aeq) level has to be either measured continuously during the reference time period or estimated on the basis of temporal sampling techniques. In the latter case, the most used in practice, the more precise isthe knowledge of the noise level temporal pattern during the reference period, the more accurate is the prediction of L{sub}(Aeq) Even if the urban noise typically varies with time, it might be classified in temporal patterns, having a specified time resolution (most frequently the hourly L{sub}(Aeq) levels) The present paper deals with this topic and describes the results of thecluster analysis carried out on a large set of experimental data of urban noise taken in some cities in Italy and Spain. The set was formed by the 24 hour time histories of hourly L{sub}(Aeq) levels, monitored in different urban sites in order to berepresentative of the situations usually occurring in the cities. Data refer not only to weekdays but also to weekends and bank holidays. In most of the sites traffic noise was the predominant noise source. The parameters of the cluster analysis, that is the algorithm for calculating the distance between clusters and the agglomeration criteria, have been varied in order to evaluate how the resulting classification groups the experimental data, also inrelation to the type of the site and of the day. The number of clusters have been selected taking into account the need of an adequate accuracy of the classification and, on the other hand, the capability of generalization. The resulting hourlyL{sub}(Aeq) patterns have been compared to the results obtained in previous studies carried out in Italy and Spain.
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