Abstract
The acoustic noise measurement standard for wind turbines provides to use a hard board placed on the ground to minimize the influence of different ground type as well as to reduce wind-induced noise. It also requires to report measurement uncertainty. Since ground surfaces of wind turbine site are believed to be variant from bare soil to grass covered with unevenness, it is necessary to acquire information concerning the ground type effects on measurements to improve measurement results. This report describes results of the tests on sound pressure level distributions due to obliquely incident sound over 1.5m diameter ground board on four different ground surfaces of cut-lawn, bare sandy soil and grown grasses. It was found that the board carefully placed on the bare soil surface avoiding making gap between the board and soil surfaces gives minimum spectrum error. Also effects of gap of the 1.0m diameter split board for acoustic measurements were examined.
