Long Range Localization of Impulsive Sources in the Atmosphere and Ocean From Focus Regions in Single Element Spectrograms

摘要

Waveguide propagation often displays transitions from one type of propagation to another as the mode number (or the take-off angle from a ray theory point of view) increases. An example of such a transition occurs when the boundary of the waveguide changes from being formed by refraction to being formed by reflection. When these transitions occur, they can result in broadband focusing of energy. These focus regions are observable in time series and in single element spectrograms. By measuring the difference in arrival times between these focus regions and knowing the group velocities involved, the range to a longrange impulsive source can be estimated, in the same way that time-of-arrival differences between seismic phases in single station seismograms are used to estimate epicentral distances. Examples of such broadband focusing in low-frequency acoustic propagation in the ocean and infrasonic propagation in the atmosphere are presented in this paper.