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

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 inn 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. (C) 1998 Acoustical Society of America. [S0001-4966(98)04208-8]