SOUND-PROPAGATION IN THE ATMOSPHERIC SURFACE-LAYER - COMPARISON OF EXPERIMENT WITH FFP PREDICTIONS

This paper presents a set of acoustical and meteorological data from a n outdoor sound propagation experiment. This experiment was done in a farm field near Rock Springs, Pennsylvania, on 7 July 1990. Meteorolog ical and acoustical measurements were recorded simultaneously during s ix different times in the day. The meteorological measurements permitt ed determination of the sound speed profiles during each of the measur ement sessions, using a method based on surface-layer similarity scali ng. The acoustical measurements allowed precise determination of the r elative sound pressure levels for a frequency range up to 3150 Hz at s ix different distances (66, 88, 125, 175, 250 and 350 m). The results show atmospheric conditions have an important effect on sound propagat ion. At medium and high frequencies, variations of the relative SPL ha ve been measured at distances as short as 62 m. These effects increase d with the distances so that variations as great as 30 dB have been me asured during that day. Comparisons with the fast field program predic tions are also presented, and amply demonstrate the accuracies of this model, especially for the downward refraction cases.