exposure meters used were calibrated against a pyrheliometer before 

 use. Little is known of the accuracy possible with an instrument of 

 this type, but, if sufficient accuracy is attainable, the use of exposure 

 meters would afford a relatively inexpensive means of measuring 

 radiation. It is recommended that the practicability of using exposure 

 meters in heat budget studies be investigated and that some compara- 

 tive experiments be conducted by the Hydrographic Office. 



c. Other radiometers 



It is known that several good radiometers have been devel- 

 oped in Europe which have not been evaluated by this Committee. 

 It is recommended that investigations continue on the evaluation of 

 existing foreign radiometers. 



2. Instruments used below water 



a„ Open ocean clarity instrument 



An instrument should be developed that is capable of mea- 

 suring the attenuation of ambient light with depth as well as trans- 

 parency in relatively clear open ocean water. It should be equipped 

 so that a number of wave length ranges could be measured on one 

 cast, thus shortening the amount of time necessary to complete a 

 cast and minimizing the chance of changes in the illumination condi- 

 tions. 



b. Water clarity meter (photocell type) 



The Visibility Laboratory recently proposed a radically new 

 design for a second generation of water clarity instruments based on 

 the principle of null balance. This design appears to promise improved 

 reliability and operation for the water clarity meter, and it is recom- 

 mended that development of the design and new instruments be followed 

 closely by this Office. 



VIII- 8 



