SECT. 4] 



439 



neglected, the total scattering coefficient s = 'I-nhNII^, where N is the measured 

 radiance of the infinite path observed and /o is the initial intensity of the plate. 

 Because of the relatively high absorption coefficients of water throughout 

 the spectrum this method has limited application to the measurement of the 

 scattering coefficient of sea-water. 



1 



^0° 60° 80° 100° 120= 



ANGLE OF OBSERVATION 



Fig. 20. Relative volume scattering function obtained by Jerlov in the Atlantic near the 

 entrance to the Mediterranean Sea for peak wavelength 465 mji.. Mean value of 30 

 records taken in the area between Madeira and Gibraltar. 



The second proposal advanced by Tyler (1957) utilizes a sample contained 

 in a watertight glass sphere on a G.E. Spectrophotometer. Using the technique 

 described, the value obtained from the spectrophotometer is the total fraction 

 of scattered light from a collimated beam passing through a fixed volume. 

 From this information the total scattering coefficient can be computed as a 

 function of wavelength. 



6. Irradiance 



From equation (3) it can be seen that, in order to measure irradiance, it is 

 necessary to use a device which collects flux according to the cosine law : 



Je — Jo cos 6. 



Since photodetector surfaces do not collect flux in this manner, an optical 



