Sound propagation for a low height impulsive source over an absorbing ground

Noise contours around military training areas are calculated by using: a) the measured source strength for the impulsive sources and b) the calculated sound propagation using a representative set of meteorological situations. For high-energy impulsive sounds the source strength is measured at distances beyond 100 meters, where peak levels are below 154 dB. A linear model is used to correct for the sound propagation from the source to the measurement position. In this way a linear source strength is determined that can be used with linear sound propagation models. Previous results showed that the source strengths at higher frequencies (above 250 to 500 Hz) were overestimated when the impulsive source is on the ground. Apparently, the calculated sound propagation over an absorbing ground, used to determine the source strength, is accounting for too much ground effect. Note that the actual meteorology and ground absorption are measured during the measurements. In this paper an impulsive reference source is used at two heights and the sound propagation is measured and calculated at increasing distances. It is shown that the measured ground effect saturates for higher frequencies. Next, an unknown impulsive source was measured and the effect of saturation was demonstrated.