

EIVER -^ ■ \ W 



RECEIVER — ^ H 

 (HYDROPHONE' 



'i 



TRAINABLE 

 TRANSMITTER 



i|^5-* OUTBOARD 

 ' ^. COMPONENTS 



Fig 10 2 STOAZA Model SM502A CTFM sonar components aboard ALUMINAUT (US, Navy) 



Compared to passage in air, light passing 

 through water is rapidly attenuated. This is 

 the result of: Absorption and scattering due 

 to the water itself, materials dissolved in the 

 water and plankton and detritus living and 

 suspended within the water. The absorption 

 of light varies with the wavelength.* Scat- 

 tering is practically independent of wave- 

 length since the particle size is usually much 

 larger than wavelengths in the visible light 

 spectrum. Larson and Rixton (4) constructed 

 a typical curve of percent transmission 

 through 20 feet of clear ocean water versus 

 the wavelength. Their graph is reprinted in 



Figure 10.4 and shows the maximum wave- 

 length transmission (78%) as being at about 

 5,000 Angstroms — the green band. This par- 

 ticular characteristic (absorption as a func- 

 tion of wavelength) is a major factor govern- 

 ing the choice of the most effective underwa- 

 ter lights for viewing. 



While there are many varieties of lights for 

 submersibles, three types are in general use: 



Quartz Iodine— an incandescent light 

 source using a tungsten filament. The "io- 

 dine cycle" precludes deposition of evapo- 

 rated tungsten on the inside of the bulb and 

 subsequent blackening. 



472 



