Influence of weather on the acoustical properties of a ground surface: measurements and models

The acoustic properties of a ground surface are well known to be affected strongly by soil moisture contents. Many studies have been conducted to quantify the effects through in-situ and laboratory measurements. The soil moisture is also well known to be influenced by continuous variability of meteorological elements such as rainfall, sunshine, and air temperature. Therefore, it is expected that the meteorological variability alters ground acoustic properties over time. For this study, an in-situ measurement campaign was held during July 2014 to January 2015 at a site in Niigata, Japan. An automatic weather station observed meteorological elements at 1-minute intervals. A buried soil moisture sensor measured water saturation in the ground near the station at 5-minute intervals. The acoustic absorption coefficient of the same ground position was measured once a day using an in-situ measurement technique. The observations showed that the absorption coefficient of the ground surface had variations with multiple timescales from days to months and seasons. Two-stage models of the influence of the weather on the absorption coefficient of the ground surface were derived from the data. The first stage models the short- and long-term effects of rainfall and the air temperature on the water saturation of the soil. The second stage models the effects of water saturation on the absorption coefficient of the ground. The derived models were found to explain the long-term and approximately half of the short-term variation of the acoustic absorption.