Assessing noise pollution in sensitive areas: Soundscape analysis in an alpine valley by psychoacoustic means

Abstract

Alpine valleys are sensitive areas due to topography, meteorology, housing, and land-use pattern, that modify noise propagation and make protection against noise pollution rather difficult. The ‘‘amphitheater’’ effect was mentioned as explanation for deviating noise-annoyance curves and health effects observed at lower sound levels. However, detailed empirical analyses are lacking. In this study a series of simultaneous, binaural sound recordings was carried out in several cross sections of the Wipp Valley along the central-European transportation route to the Brenner pass. During 6 weeks a wide variety of day- and week times was sampled with variable wind (‘‘Foehn’’) and weather conditions (dry, rain, snow). Sound recordings were paralleled by meteorological recordings near the source and on the slope. First analyses have revealed several facts. (1) The assumption of linear sound propagation to the slope is seriously in error. (2) Tonal components from gearboxes are a significant feature in the slope recordings. (3) Low-frequency modulations make the sound more intrusive on the slope—while near the source this feature is better masked. (4) Low background sound levels (<30 dB,A) on the slopes are in sharp contrast with incoming sound levels (52 dB,A,Leq about 1200 m from the source). (5) Meteorology leads to substantial changes in measured sound levels.