practice, any combination of sea state and shipping may be encountered. As 

 may be seen from Figure 5, the sea state noise dominates the high frequencies, 

 and shipping noise controls the low frequency region of the ambient noise 

 spectrum. 



3. Calculation of Detection Range . The detection range 

 calculations ate carried out for two sound propagation conditions: 



a. Spherical (inverse square law) spreading, where 

 TL = 20 log r + r x 10-3 



b. Cylindrical spreading, where 

 TL = 10 log r + r x 10-3 



The latter is the better sound transmission, and leads to the 

 upper limiting detection ranges. In all cases the value of attenuation 

 coefficient ( ) is taken from Figure 2. The calculated detection ranges are 

 given at the bottom of Tables 1, 2, and 3. 



V. DISCUSSION 



It is clear from the calculations above that there is a distinct 

 possibility that the sounds radiated from the noisier oil platforms, either in 

 drilling or production mode, may be audible to whales out to great ranges 

 under favorable sound propagation and noise conditions. It must be noted that 

 the range is \jery dependent on the specific propagation and ambient noise 



G-31 



