Infrasonic interferometry applied to microbaroms observed at the Large Aperture Infrasound Array in the Netherlands

We present the results of infrasonic interferometry applied to microbaroms, obtained from ambient noise. For this purpose the 'Large Aperture Infrasound Array' (LAIA) was used, which has been installed in the Netherlands. Pre-processing appeared to be an essential step in enhancing the microbarom signals from ambient noise that strongly influences the results of the interferometry. Both the state of the atmosphere and the noise characteristics are taken into account to assess the strength of the cross correlation. The traveltime of the microbaroms between two stations is determined through cross correlating the recordings. By calculating the cross correlations between all 55~station pairs of LAIA we are able to find the traveltime of microbaroms up to a inter-station distance of 40.6 km. Using the strength of the cross correlations we are able to show that the coherence of the microbaroms along the direction of arrival is higher than orthogonal to it. A comparison of the atmospheric state, with a cross correlation, over a period of 10~days, reveals that the infrasound propagation over the array is correlated with the tropospheric temperature and wind. Based on the cross correlations between the three closest stations, we are able to passively estimate the effective sound speed and the wind speed as a function of time.