APPENDIX B. ALGORITHMS 



The CZCS provides estimates of the near surface concentration of phyto- 

 plankton pigments (defined to be chlorophyll a and its associated phaeo- 

 pigments) by measuring the spectral radiance backscattered out of the 

 ocean. This radiance scattered out of the ocean and reaching the top of 

 the atmosphere comprises only a small portion of the total radiance 

 measured at the sensor. In general, the sensor radiance U(x) (x is the 

 wavelength) can be decomposed into L^x), the radiance due to photons 

 that never penetrated the sea surface, and t(x)L (x), the radiance due 

 to photons which were backscattered out of the water (the water-leaving 

 radiance) and diffusely transmitted to the top of the atmosphere, i.e., 



L t (X) = L X (X) + t(X)L w (X). (1) 



All of the information relating to the oceanic constituents such as the 

 chlorophyll concentration is contained in L (x). 



W 



Schemes for extracting L ( x) from L. (x) are referred to as 'atmospheric 



w u 



correction' algorithms, and empirical relationships used to derive the 



pigment concentration from the extracted L (x) are called 'bio-optical' 



w 



algorithms. 



B.l BIO-OPTICAL 



Most early studies concerning the remote sensing of ocean color (Clarke 

 et al., 1970; Arvesen et al., 1973) were directed toward the extraction 

 of the surface chlorophyll concentration from the spectral radiance 

 upwelling above the sea surface. Chlorophyll a is the pigment present 

 in living plants responsible for photosynthesis. In the ocean, this 

 pigment is present in microscopic organisms called phytoplankton, which 

 form the first link in the marine food chain. In productivity studies, 

 chlorophyll a_ is usually taken as a measure of phytoplankton 'biomass' 

 (Piatt et al., 1975). 



B-l 



