THE VARIABILITY OF BOTTOM REFLECTED SIGNALS USING THE DEEP RESEARCH VEHICLE ALVIN
NAVAL OCEANOGRAPHIC OFFICE NSTL STATION MS
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Two dives were made using the Deep Research Vehicle ALVIN to investigate the variability of normal incidence bottom reflected signals at 12 kHz. The measurements were made over a locally smooth bottom in a water depth of 4750 feet in the Tongue of the Ocean. Approximately 270 bottom reflected signals were recorded at each of three levels above the bottom 500, 2000 and 4500 feet. For each depth, frequency distributions, autocorrelation coefficients, and coefficients of variation were computed using both relative peak amplitude and energy levels. The results indicate that significant changes in bottom reflectivity can occur in a short duration and that the observed variations are probably caused by changes in the reflective characteristics of the ocean bottom combined with horizontal drift of the vehicle. Changes in the bottom are suggested by the data collected at the deepest level, which exhibits a pronounced shift in signal level and a bimodal frequency distribution of pulse amplitudes. In addition, the observed fluctuations generally increase with increasing distance above the bottom.
- Physical and Dynamic Oceanography
- Marine Engineering