SECT. 4] 



LIGHT 



436 



irradiance and sample volume are used to compute the volume scattering 

 function between 20° and 160°. These values can then be integrated to give the 

 total scattering coefficient (see equation 21), and the forward and backward 

 scattering coefficients. 



More recently Jerlov has developed the instrument shown in Fig. 16 for 

 studying the volume scattering function of ocean water. The detector in this 

 instrument is fixed in a vertical position as shown in the figure. The lamp 

 assembly can be released to turn slowly around the point, p, carrying a series of 

 semicircular ly arranged stops with it. These stops are designed to maintain a 



Fig. 15. Scattering meter designed by Tyler (1958) for in situ measurements oi a{d). 



sample volume of j&xed size at jp. Relative values of the volume scattering 

 function are obtained at 12 angles from 10° to 165°. 



Measurements of the scattering of ocean-water samples at a fixed, angle have 

 been found useful for characterizing waters of various types, and for studying 

 the particle distribution in the ocean. Jerlov (1953) has developed the equip- 

 ment shown in Fig. 17 for this purpose and, in his investigations, has used the 

 premise that a direct correlation exists between his measurements at 45° 

 from the beam and the total scattering coefficient. 



The equipment consists of a modified Zeiss turbidity meter and a Pulfrich 

 photometer set at the desired scattering angle. The volume of the sample is 

 constant by virtue of the fact that it is contained in a glass cylinder which is 

 immersed in water to reduce interface reflection. 



Measurements are obtained by visually matching the scattered light to a 

 comparison glass illuminated directly by the source. This is done in the spht 

 field of the Pulfrich photometer. Since the radiance of the comparison glass is 



