response of the photocells is made similar to the response of the 

 average human eye by means of special filters on each cell. 



The deck unit consists of a photocell for measuring surface illumi- 

 nation, an electronic unit, and a recorder. Any of the four parameters 

 may be recorded separately, or each may be recorded in succession 

 by an automatic sequencing arrangement. 



This water clarity meter has a number of limitations. Like all 

 optical equipment it is easily knocked out of alignment. However, 

 good instructions are provided for the instrument, and it is easy to 

 realign. The vertical distance between the h-meter and the Alpha- 

 meter light path, approximately two feet, makes correlation between 

 the two meters rather difficult. The error of the Alpha-meter is 

 approximately two percent. Good results can be obtained with this 

 instrument when it is used by highly trained oceanographers. It is not, 

 therefore, recommended for use as a standard survey instrument. 



C. CONCLUSIONS AND RECOMMENDATIONS 



With the growing importance of heat budget and thermal structure 

 studies required for sonar forecasting, an urgent need exists to meas- 

 ure and predict the radiant heat exchange through the sea surface 

 and the distribution of heat with depth. It follows then that the develop- 

 ment of adequate radiation measuring instruments is a necessity. 



1. Instruments used above water 



a. Geir and Dunkle radiometer 



The measurement of long wave radiation, to a large extent, 

 has been neglected in the field of oceanography. The Geir and Dunkle 

 type radiometer has been used successfully in measuring long wave 

 radiation over land, over snow, and over fresh water. The modifi- 

 cation of this instrument as an oceanographic tool should be investi- 

 gated. Of the radiometers investigated, this instrument appears to 

 offer the best promise for a seagoing instrument that will measure 

 both daytime and nighttime incoming long wave radiation as well as 

 back radiation. 



b. Photographic exposure meters 



Photographic exposure meters have been used with success 

 in measuring incident light for photosynthesis studies by P. R. Nelson 

 and W. T. Edmondson of the U. S. Fish and Wildlife Service. The 



VIII- 7 



