James H. Wilson
Naval Postgrad. School, Dept. of Oceanogr., Monterey, CA 93943
J. Huw Davies
Robert H. Bourke
Naval Postgrad. School, Monterey, CA 93943
Recently, an active broadband dispersion phenomenon was observed
empirically in measured data for propagation paths within the mixed layer (ML)
[Dien et al. (1994)]. This so-called Wilson Dispersion Phenomena (WDP) is
explained simply by noting that high-frequency energy trapped within the ML
travels faster than low frequencies that diffractively ``leak'' out of the ML.
Thus WDP is a useful technique for distinguishing between reflectors in the ML
and reflectors below the ML. More recently it was shown that the WDP may occur
in other shallow-water environments [Davies et al. (1994)]. Several sound-speed
profile (SSP) environments are examined, using normal mode theory, for depth
dependence of broadband frequency dispersion. A very conservative approach is
taken regarding frequency reflectors. Geoacoustic properties of the bottom are
not addressed. SSPs for which dispersion depth dependence is observed within the
water column for a lossy bottom are labeled useful for active classification.
Future research including geoacoustic properties of the sub-bottom may lead to a
wider range of SSP and geoacoustic sub-bottom environments which produce
dispersion depth dependence. It has been empirically observed that bottom
reflectors (the primary false targets) never have significant dispersion and are
spread over much longer times than reflectors within the water column. [sup