Recording wind microstructure with a seismograph

Abstract

In an effort to characterize the effects of atmospheric waves on seismic sensors at the surface of the earth, we used geophones to perform some simple experiments allowing us to “watch” the wind. By examining the wind noise on the resulting seismograms, we were able to characterize the microstructure of atmospheric wind gusts at a horizontal scale of 1 to 10 m. In a first experiment to detect the wind-induced wave field, we placed 96 geophones on the ground in a straight line aligned parallel with the wind at intervals of 0.3 m. We recorded the resulting data using a 96-channel exploration seismograph. In essence, the seismograph system served as a linear array of 96 ground-level wind sensors. On a 1- to 2-m scale, wind-gust details became apparent after the seismograph had recorded for a period of 7.5 s. When wind-gust speeds were between 4 and 7 m/s (as measured directly from the time-and-distance relationships obtained from the seismogram), the wavelength of the gusts was between 3 and 6 m. In a second experiment, we used an array consisting of three parallel lines of 32 geophones each and were able to detect the lateral components of wind motion and turbulence relative to the long axis of the array. We noted variations in both space and time in the effect of the wind gusts on the geophones. The sensing system we describe is preliminary; however, when further refined, it may be a useful way of looking at the microstructure of atmospheric motion near the ground. The data we obtained also suggest that when models are constructed and near-ground atmospheric observations are made using grid spacings of more than 1 m, the results may be subject to serious spatial-aliasing effects. The authors offer these results in the hope that they will stimulate new, cross-disciplinary scientific inquiry. Moreover, applications of the technique might include the generation of data to support improved modeling of atmospheric turbulence at meter scales, which could be of interest to those requiring information about wind shear, wind-induced soil erosion, the dispersion of pollutants and toxins, and other subjects of interest.