Progress in understanding seismic wind noise

Abstract

Previous work at NCPA on predicting and measuring wind noise in the ground used a quasistatic calculation employing Shield’s wind noise correlation function. This method predicted the vertical displacements at the surface well, but under predicted the horizontal displacement and predicted a rapid decay of levels with depth that was not observed in the measurements. A new measurement of the wind noise correlation coefficients using flush mount microphones was presented at the Seattle Meeting (2aPa1). In this talk additional measurements and improved methods for evaluating the coefficients are described. An improved calculation of the seismic levels due to wind induced pressures at the ground has been developed based on the wavenumber-frequency analysis developed for studying airframe noise due to turbulence. This calculation correctly predicts the surface vertical component and the near constant seismic level in the first 40cm of the ground. It still under predicts the horizontal component, but the under prediction is smaller than that predicted by the quasistatic calculation. [This research was sponsored by the Department of the Navy, Office of Naval Research under ONR Award No. N00014-18-2489.]