(1981) use an empirical relationship derived by Austin and Petzold 

 (1981) for Case 1 waters; 



L w (670) = 0.0829L W (443) [R(13)] _1 ' 661 (14) 



and solve the resulting set of nonlinear equations iteratively. 



As mentioned previously, in Gordon et al. (1980) S(x,X ) was determined from 



the water-leaving radiance measured at one position in the image from a 



ship. It is, however, desirable to be able to determine S(x,x ) without 



resorting to any surface measurements. The key to effecting a solution 



to Equations 12 and 13 or 14 is the determination of S(x,X^) or 



equivalently e(x,X.). This is accomplished using the concept of 'clear 



water radiances.' Gordon and Clark (1981) have shown that, for 



3 

 phytoplankton pigment concentrations less than about 0.25 mq/m , the 



water-leaving radiance in the green, yellow, and red CZCS bands can be 



written 



L w ( A) - L w ( x) N cose o x 



exp[-(t r /2 + T 0z )/cose Q ] , 



(15) 



where [L ] M ,the normalized water-leaving radiance, is 0.498, 0.30, and 



less than 0.015 mW/(cm m ster) for 520, 550, and 670nm, respectively. 



3 

 Thus, if a region of image for which C < 0.25 mg/m can be located, 



Equations 7 and 10 can be used to determine e (520,670), e (550,670), and 



e(670,670). e (443,670) can then be estimated by extrapolation. An 



important aspect of this algorithm is that no surface measurements of 



either <L(x)> or of any properties of the aerosol are required to 



effect the atmospheric correction with this scheme. 



B-14 



