On the Use of Infrasonic Ambient Noise in Imaging the Atmosphere

Abstract:

To retrieve information on the wind and temperature in the (upper) atmosphere, determinsitic transient signals, like those from volcanoes, can be used. Both the traveltime and the slowness of the signals can be translated to variations in the wind and temperature structure along the source-receiver trajectory. In such a case, ground-truth about the source location and sometimes orgin time are necessary to restrict the analysis. However, sources with such a ground-truth are limited to certain geographical locations and have a sparse temporal availability. It is therefore attractive to use the ambient noise field, which is continuously present from a variety of directions. In theory, the cross correlation of the ambient noise field between two receivers should reveal the acoustic lag time between these receivers. With a known distance between the receivers, this lag time can be translated to the acoustic velocity which in turn is a function of the wind and temperature. In this presentation, the theory and results of this so-called ambient noise interferometry will be shown.