7. Where high definition is required it has been used as a 

 view finder with still and/or motion picture cameras. 



8. Observations have been made for marine engineering 

 projects. 



Basically, two types of television systems are available for 

 making underwater observations. These are the image orthicon 

 and the vidicon. Where low light levels are encountered and high 

 resolution is a requirement, the image orthicon is generally re- 

 commiended. When artificial illumiination is to be used and cost is 

 an important consideration, then a vidicon system may satisfac- 

 torily be employed. 



A wide range of visibility is encountered in the ocean. Many 

 coastal areas limit viewing range to as little as 2 feet, while off- 

 shore, visibility ranges of well over 100 feet have been reported. 

 Of great importance in underwater visibility is the loss of inten- 

 sity of light, caused by part of the light being reflected from the 

 surface, by absorption, and by scattering. Horizontal scattering 

 of light beneath the surface varies considerably with depth and lo- 

 cality. In coastal waters with much wave action the planktonic life 

 and particles of minerals cause excessive turbidity, and in some 

 places half the total light is absorbed in the first 10 feet. 



Artificial lighting was found to improve contrast considerably. 

 However, for optimum results particular care must be used in 

 the physical arrangement of lights. The light source should be 

 placed as near the subject as possible to reduce back scattering 

 from particles. 



Observations made with the image orthicon system (tube type 

 #58Z0) of our Woods Hole Laboratory have shown that adequate vi- 

 sibility of 20 to 30 feet, with natural illumination, was consistently 

 found in certain areas off New England in depths of up to 25 fathoms. 

 One February, on the northeast edge of Georges Bank, we were 

 able to observe, at 40 fathoms with natural illumination, the 

 headrope of a trawl approximately 50 feet from the camera. It 

 should be noted that image orthicons now available are more sen- 

 sitive than the one we used. 



The U. S. Navy Bureau of Ships has reported nnaking obser- 

 vations up to 100 feet away at depths of 800 feet in an area off 

 Newfoundland with the use of high sensitivity image orthicon 

 cameras. Observations have been reported in depths up to 500 

 meters without the aid of artificial illumination. 



MR. J. R. R. HARTER (BUSHIPS): In November 1954 a cooperative 



249 



