The determination of signal coherence length based on signal coherence and gain measurements in deep and shallow water

Abstract

Experimental measurements of signal coherence and array signal gain are presented for both deep- and shallow-water sound channels. The signal gain is related to the transverse horizontal coherence length through relationships from the statistical theory of antennas. Signal gain measurements in the transverse direction are proffered as a practical measure of coherence length for both broadband and narrow-band signals. With this technique, measurements at frequencies near 400 Hz are presented and show for the deep-water cases that lengths on the order of 100 wavelengths can be achieved to ranges of 500 km; while in the variable downward refraction conditions of shallow-water waveguides with sand-silt bottoms, lengths on the order of 30 wavelengths to ranges of 45 km are realized. The measurement of broadband and narrow-band coherence is discussed with emphasis on the role of partly coherent noise backgrounds, multipath interference effects, and averaging constraints. Experimental results are interpreted with deep-ocean coherence models consistent with sound scattering from the ocean volume and Gaussian coherence function for the shallow-water waveguide.

Acoustic Ducting, Reflection, Refraction, and Dispersion by Curved Nonlinear Internal Waves in Shallow Water

“…17(d)], and the value looking at one particular steering angle. It is seen that these numbers have an average of about 25 wavelengths, in good agreement with the work of Carey [25]. Also, during periods of strong internal wave activity, this correlation length decreases significantly, in agreement with what was found numerically by Finette and Oba [4] and previously found in the limited analysis of Collis et al [23].…”

Horizontal coherence of low-frequency fixed-path sound in a continental shelf region with internal-wave activity

“…Among them, covariances have been computed for long-range low-frequency propagation (Duda et al, 1992), and horizontal correlation scale estimates have been tabulated (Carey, 1998;Carey et al, 2006). The latter were in the range of tens of wavelengths for shallow water.…”

Observed limiting cases of horizontal field coherence and array performance in a time-varying internal wavefield

“…5 Under the assumption that noise is uncorrelated between the sensors, the gain degradation can be related to signal coherence length. Signal gain G c is calculated as…”