Further Analysis of Helicopter Noise Experiments in an Urban Environment

A previous paper by the authors [J. Acoust. Soc. Amer. (in press)] discusses preliminary analysis and interpretation of recent experiments in which recordings were made while a helicopter flew over (1) an array of microphones placed in an open field, and (2) a similary array placed in the center of a city street surrounded by tall buildings. The present paper examines (1) the frequency dependence of the urban enhancement effect, (2) the variation in noise-versus-time profiles with microphone location, and (3) the reproducibility of the helicopter flyover noise data. Third-octave-band spectra of the open field and urban recordings are exhibited and discussed and simultaneously recorded data by microphones in the center and at the side of the street are exhibited. [Research supported by U. S. Department of Transportation.]