Ambient noise and signal uncertainties during the summer shelfbreak primer exercise

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Author
Abbot, Philip
Gedney, Charles
Dyer, Ira
Chu, Ching-Sang
Date
2002Metadata
Show full item recordAbstract
Uncertainties in noise Ievel, andin signallevel after long-range (42 km) acoustic shallow
water transmissions, from a pulsed source, are determined from the summer shelfbreak
PRIMER experiment. Fluctuations over the 1 0-day period are not stationary, but are
rendered so by tracking the wandering of their means. Then narrow-sense stationary
probability density functions are obtained of ambient noise and signal peak transmissions
from a match-filter output with time-bandwidth product = 1. The data are centered at 400
Hz, in a 100 Hz bandwidth, and analyzed from three individual hydrophones of a vertical
line array. The ambient noise fluctuations closely follow the phase-random Log-Rayleigh
density, with standard deviation cr = 5.6 dB. Signal peak statistics are determined from
demeaned 50 s samples. The signal statistics over an 8-h period are approximately
similar, but not identical, to those over the entire 10-day period. The signal has narrower
histograms (cr "' 0.8 dB) than the noise. Log Chi-Square densities, fit to the signal
histograms, suggest that about 30 equal intensity components contribute to the
fluctuations, many more than can be attributed to the idealized modal structure in the
shelfbreak duct. This suggests that either strong scattering affects the signal transmission,
or the signal process is not fully phase-random.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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