Biological Factors 



AMBIENT SOUND 



Biological and other sounds which 

 contribute to the total ambient noise are 

 identified and measured from the tower. 



The low background noise permits 

 the study of a wide variety of sounds of 

 biological origin, and is favorable for 

 high-frequency acoustic tests. There is, 

 however, some low-level water noise be- 

 low 10 kc/s which is caused by waves 

 surging against the tower framework. 



Two distinct periodic variations 

 in underwater noise level are observed. 

 The first has a semidiurnal period in the 

 band between 200 and 1200 c/s. Higher 

 intensities are noted around sunrise and 

 sunset in summer. The second variation 

 has a period of 25 to 40 seconds and is 

 observed only at night and only in the late 

 spring and summer. It is commonly 3 to 

 6 dB above the background, but a maxi- 

 mum of 16 dB has been recorded. It 

 occurs in the limited 300- to 800-c/s 

 band, with a peak amplitude at 450 c/s. 



Both ambient sounds are apparently 

 biological in origin and are related to 

 sandy bottoms. Two members of the 

 croaker family; spotfin, Roncador 

 stearnsi; and yellowfin, Umbrina roncador, 

 are believed to be largely responsible. 



Listening hydrophone is placed in view of the tele- 

 vision camera in an attempt to identify the organisms 

 which produce sounds in the sea around the tower. 

 View looking down rail track. 



