however, they do not show the variability. This is probably due to the fact 

 that these measurements were taken in "deep" water, and that all measurements 

 were made from a single, distant measuring site. 



The data shown in figures 1-6 indicate that based on available sources, 

 the noise from offshore oil and gas drilling activities can potentially cover 

 a broad frequency range (10 Hz to 10 kHz) with average source levels from 130 

 to 180 dB re 1 yuPa at Im. The major tonal components are below 1.0 kHz with 

 the major energy below 200 Hz. Signal-to-noise ratios may approach 80 to 100 

 dB above the ambient levels, which means that levels of this magnitude would 

 not be completely attentuated until they reached a point 30 to 50 nautical 

 miles from the source. 



A-6 



