Wind-generated ambient noise in a topographically isolated basin: A pre-industrial era proxya)
The TOTO, a geographically and acoustically isolated deep basin surrounded by the Great Bahama (coral) Bank, is a very quiet acoustic environment [from Szlyk (2002)].
Twelve monthly climatological SSPs for the location of the acoustic array in TOTO, based on GDEM-V (2003).
Frequency vs frequency plot of NSL at 1 kHz vs NSL at 2 kHz was used to establish the spectral shape of the ambient noise in TOTO. The solid line shows the “best grouping” straight line fit between the NSL at the two frequencies. Maximum and minimum NSLs for which the best fit line is considered a valid approximation are indicated by a “+” symbol. Dashed lines indicate regions of extrapolation of the regression.
NSL vs wind speed (kt). Small data points depict 495 NSL values used to establish the correlation with integer values of the log of the wind speed. Diamonds depict mean values of NSL for each value of wind speed. Solid line indicates the linear regression based on mean values (diamonds). Dashed lines indicate regions of extrapolation of the regression.
Wind-dependent ambient NSL in TOTO as a function of frequency. The solid lines depict the NSL for the indicated values of wind speed, which fall within the range of validity of Eq. (4), as specified in Table III, while the dashed lines (without circles) depict the curves which have been extended beyond the range of validity. Wind speeds which fall outside the range of validity of Eqs. (5) and (6) are indicated by an asterisk (*). The dashed curve with open circles indicates the lower limit of validity for the spectral shape equations [Eq. (4)]. The dashed curve with closed circles indicates the minimum background ambient noise levels recorded during the observation period.
Minimum background ambient noise levels recorded in the TOTO during the observation period (dashed curve with closed circles) compared to Wenz’s canonical “lower limit of prevailing noise” curve (thick broken dashed curve), results from Cato’s (1976) study in a very quiet acoustic environment (shaded area), and an estimate of typical open-ocean noise level for “light shipping” and sea state zero (lower solid curve), based on Urick (1983). TOTO NSL for sea state 2, corresponding to 9 kt (4.6 m/s) wind speed (dashed curve), is also plotted against a Urick-based estimate of open-ocean noise level for light shipping and sea state 2 (upper solid curve).
Best fit coefficients for Eq. (3).
Best fit coefficients for Eq. (4).
Range of validity for Eq. (4).
Article metrics loading...
Full text loading...