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ACOUSTIC DAYLIGHT-HOW TO "SEE" IN THE 



DARK 



Researchers at Scripps Institution of Oceanography led by Michael Buckingham 

 have developed a new imaging technology that allows them to "see" under water 

 using naturedly occurring sounds. Called Acoustic Daylight, the technology uses the 

 sound generated by bubbles in the ocean. When these bubbles come into contact 

 with an object, the noise they produce changes. By analyzing these changes, it is 

 possible to create a visual image of the object and display it on a monitor. 



Acoustic Daylight pronuses to be useful for underwater navigation and salvage, and, 

 because the new technology is not detectable, it may prove useful for defense 

 purposes such as detection of mines and submarines and protecting harbors and 

 moored ships. 



For many years, the principal means of probing the ocean using soimd has been 

 through the use of active or passive techniques. With an active system, an object is 

 illuminated by a pulse of sound, such as sonar, and its presence inferred from the 

 echo it produces. The passive approach involves listening to the sound that an 

 object itself emits, such as engine noise. 



"What we are proposing is a new method of employing sound in the ocean, which 

 is neither active nor passive," Buckingham said. "It relies on the naturally 

 occurring ambient noise field in the ocean as the sole source of acoustic 

 illumination." 



Noise in the ocean is created by breaking surface waves that create large numbers of 

 bubbles. The bubbles emit noise, and the sound is dispersed throughout the ocean 

 to great depths. The resulting sound is comparable to sunlight, which spreads 

 evenly to all space available. The presence of an object in the ambient noise field 

 modifies the field by scattering acoustic energy in all directions. This scattered 

 radiation can be focused onto an image plane by an acoustic lens, processed by 

 imaging electronics, and displayed on a computer monitor. 



SCRIPPS INSTITUTION OF OCEANOGRAPHY 

 UNIVERSITY OF CALIFORNIA, SAN DIEGO 



