Extraction of seabed properties in mid-frequency range using waveguide invariant applied to broadband signals

One of the fundamental problems in shallow water environments is to assess the seabed properties. The waveguide invariant can be used in both passive and active sonar processing, source ranging, time reversal focusing, and in geoacoustic inversion processes. In Pekeris waveguide, the waveguide invariant value is approximately 1 and the slope of the interfering acoustic intensity fringes relates to the bottom sound speed. Using the slope of the striations as a variable, the spacing of the interference in range (or frequency) can be related to the penetration of energy into the bottom. The depth given by spacing of real arrivals has an effective depth of penetration which depends on the geoacoustic properties of the bottom sediments. Here, we study the frequency dependence of the waveguide invariant due to sediment layer structure and physical properties and provide a detailed data/model comparison for a shallow water range independent waveguide and extract the seabed properties for the frequency band 1.5 to 4.0 kHz using recent data obtained in shallow water environments. [Work supported by ONR 321OA.]