Using the waveguide invariant to analyze Lofargrams

摘要: Brekhovskikhi and Lysanov introduced the concept of a "waveguide invariant" to broader audience. Assuming horizontal array incoherent processing, they showed how measured acoustic intensity produced by distant source would exhibit striations when plotted versus range frequency. The are consequence interference between propagating modes. A similar effect can also be observed data processed coherently as with beamformer. In practice, passive sonar system often displays its beamformed output spectrum evolving in time. These plots, called LOFARgrams, typically generated multiple look-directions present work, LOFARgrams related those processing. Equations derived for trajectories striations. Numerical examples presented. Sources located both above below thermocline considered.