Calibrations were recorded on the magnetic tape at each Alaska site by 

 means of a Bruel and Kjaer Type 4223 hydrophone calibrator. This method 

 calibrates the entire system by applying a knov;n pressure to the hydrophone, 

 amplifying the signal, and recording it. A signal of 250 Hz is used, v;hich is 

 recorded on both the FM and direct-record channels. Voice commentary was put 

 on one track of the recorder to record gain settings and general conditions as 

 the measurement continued. 



For this report, a preliminary analysis was done with a General Radio 

 Model 1921 Real Time Analyzer. This instrument analyzes in one-third octave 

 bands with band centers starting from 25 Hz. The FM and direct channels were 

 each analyzed at periods in the recording judged to be free of overload on the 

 FM channel due to low frequency pressure changes. The tape speed was then 

 doubled, ard the FM channel analyzed again. This allowed analysis down to a 

 12.5 Hz centered one-third octave band. A playback was also made of the 250 

 Hz calibrate signal on both FM and direct-record channels to allow absolute 

 levels to be determined. Voice comments relative to gain settings, location, 

 hydrophone depth, current conditions and other relevant information were noted. 



The one- third octave band levels were then tabulated and plotted in 

 figures 7 to 13. 



The data taken at Platform Molly showed that inacliinery noise in the water 

 was not at a level above ambient water noise. The recordings were played back 

 over a broad-band reproducing system, and experienced listeners could b.irely 

 detect machinery noise in the predominant soa noise. The major machinery 

 noise at Rincon was a submerged firewater pump, "but this was largely masked by 



D-6 



