Investigation and remediation of munitions and explosives of concern (MEC) at marine sites are both time consuming and expensive. MEC assessment in marine environments has additional challenges compared to terrestrial sites, including the high cost of marine operations,
the general absence of surface sweeps prior to geophysical assessments, the difficulty of quick or effective site reconnaissance activities, and high levels of clutter in ports, harbors, and bays. Consequently, a high payoff exists for effective methods of feature extraction and data fusion
for improved assessment in marine settings. Recent site investigations have pointed to the potential of utilizing innovative geophysical sensing and new methods that directly link MEC experts to enabling technologies. We present two case studies to highlight the benefits of combining various
technologies to provide the information needed for comprehensive munitions site characterization. This approach has been successful for both time-critical response activities and longer-term remedial investigations.
The relationship between the signal bandwidth and the coherence of high frequency, surface forward scattered underwater acoustic signals has been investigated experimentally and compared with available theory. Acoustic measurements were made under ONR sponsorship (the ARL Program) during 2000 [J. G. Keranen et al., J. Acoust. Soc. Am. 109 (2001)] and again in 2002, both times in deep water off the coast of San Diego. Transmitted signals consisted of 0.1 to 1.0 ms CW pulses and 500 Hz to 22 kHz wide linear frequency modulated sweeps using center frequencies of 18 to 46 kHz. Concurrent environmental measurements included water temperature, current speed and direction, directional wave height and wind speed. An analysis of the data is focused on how the coherence of the surface forward scattered path depends upon the signal bandwidth. We evaluate the usefulness of the frequency coherence bandwidth parameter [P. H. Dahl, IEEE J. Oceanic Eng. 26(1) (2001)], and compare measurements with time spread-based theoretical predictions [J. C. Reeves, Ph.D. thesis, UCLA, 1973; M. H. Brill et al., J. Acoust. Soc. Am. 75 (1984)]. [Work supported by ONR under Award No. N00014-02-1-0156.]
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