Observation of Stable Sound Field Components in Lake Ladoga

The paper presents the results of processing measurement data on the spatiotemporal structures of sound fields in Lake Ladoga. Measurements were taken with an extended vertical receiver array. The aim of processing was to isolate the field components that were stable with respect to small variations in the waveguide parameters. Since a model of the medium is inevitably inaccurate, such components can be predicted with greater accuracy than the total field. In terms of the ray approach, a stable component is generated by a beam of rays propagating over close trajectories. The discussed experiment analyzed sound fields excited by a point source that emitted wideband pulses, as well as the fields of wave beams excited by the emitting vertical array at fixed frequencies. In both cases, the processing results showed that the isolated stable components, as expected, coincide substantially better with the prediction of theoretical calculation (by the wide angle parabolic equation method) than with the total wave field.