SECTION I. 



ESTIMATED SOURCE LEVELS FROM OFFSHORE OIL AND GAS DRILLING ACTIVITIES. 



Source levels for six activities and ambient noise spectra corresponding 

 to these areas are shown in figures 1-6. Each figure contains two pieces of 

 information that describe the acoustic environment in the vicinity of the 

 drilling activity. The source level data for an activity is plotted in the 

 upper half of each figure, and ambient noise spectrum levels are plotted for 

 the general area in which the measurements were made in the lower half of each 

 figure. Data at 20, 100, 200 and 300 Hz are from the ASEPS prediction model, 

 and are plotted as the average of four predicted values plus or minus a 

 standard deviation for winter (o) and summer (.) seasons. (ASEPS prediction 

 model data were obtained from NOSC, San Diego, for specific lease areas.) The 

 ambient noise levels as a function of shipping traffic and wind speed are from 

 published sources (Urick, 1967). 



Signal-to-noise (S/N) ratios may be estimated from these figures by 

 subtracting the spectrum level noise from the source level at a particular 

 frequency. The S/N ratio can be used to estimate the maximum range at which 

 the sound may be detectable for these ambient noise conditions. 



Prudhoe Bay Area 



Figure I shows the major tonal components from two drilling sites in the 

 Prudhoe Bay area: the NIAKUK 3 well, on a man-made gravel island, and the 

 Reindeer Island Coast well, on a natural barrier beach island (Malme and 

 Lawski, 1979). The source levels are plotted as averages of received levels 

 from several ranges (1,000 to 1,600 m) corrected for attentuation. The 

 variability indicated by the standard deviation probably indicates changes in 

 (1) propagation characteristics in shallow water, and (2) wind speed, ice 

 movement and activity levels at these sites during the measurements. 



These data show little difference in the noise levels; however, they 

 have different tonal components. Although the bandwidth of the receiving 

 equipment was reported to be at least 20 kHz, the authors noted that no useful 

 data were obtained at frequencies higher than 8 kHz, and that the acoustic 

 levels in this high frequency region were low. 



A-4 



