Multipath correlation at mid-frequency in a convergence zone

Area of Science:

• Oceanography
• Acoustics
• Wave Propagation

Background:

• Convergence zone (CZ) propagation involves a limited number of eigenrays with specific turning points.
• The geometry of CZ propagation results in minimal random internal wave scattering over its ~60 km range.
• This suggests potential correlation of CZ multipath over limited observation intervals.

Purpose of the Study:

• To apply wave propagation theory in random media to CZ propagation.
• To predict the correlation of CZ eigenrays within a Garrett-Munk internal wave field over a finite observation interval.
• To compare theoretical predictions with experimental data from the Philippine Sea.

Main Methods:

• Utilized the theory of wave propagation in random media.
• Applied the Garrett-Munk internal wave model.
• Estimated complex amplitudes of multipath arrivals using beamforming with a vertical line array.
• Analyzed 5.5 kHz sinusoidal transmissions.

Main Results:

• Theoretical predictions indicated correlated multipath over observation intervals of 100–200 seconds.
• Experimental data from the Philippine Sea showed significant correlation of multipath arrivals over approximately 27 seconds.
• The observed correlation in experimental data aligns with the theoretical framework.

Conclusions:

• The study provides evidence supporting the hypothesis of correlated multipath in CZ propagation.
• Experimental results validate theoretical predictions of eigenray correlation over finite observation intervals.
• Findings contribute to understanding underwater acoustic propagation in dynamic ocean environments.