QUALITY OF UPWELLING RADIANCE RETRIEVED FROM COASTAL ZONE 
COLOUR SCANNER (CZCS) DATA FOR OCEAN COLOUR DETERMINATION 
by 
S.M. SINGH 
Carnegie Laboratory of Physics, 
UNIVERSITY OF DUNDEE, 
DUNDEE DD1 4HN, 
Scotland, U.K. 
ABSTRACT 
In this paper we shall begin with a brief discussion on the inflight 
calibration quality of the Coastal Zone Colour Scanner (CZCS) detector. 
The atmospheric correction algorithm currently in use is based on the 
assumptions that (i) the aerosol path radiance is not attenuated by the Rayleigh 
atmosphere, (ii) the Rayleigh path radiance is not attenuated by the aerosol 
atmosphere and (iii) the azimuthal angle of the satellite-sensed radiation is a 
constant. We have developed another algorithm which does not use these assumpt- 
ions. However, because of limited space available, the details have been 
omitted. Some of the difficulties associated with these atmospheric correction 
algorithms are discussed. The water-leaving radiances obtained from these two 
algorithms show that there could be a significant effect on the chlorophyll-like 
pigment algorithm. 
We have also included a brief discussion on the uncertainty in the 
chlorophyll-like pigment concentrations due to factors such as the uncertainty 
in the solar irradiance on the top of the atmosphere, variation in the salinity 
and temperature of the sea-water, and differences in the values of the refractive 
index of sea-water used by different investigators. It is concluded that the 
uncertainty in the solar irradiances could have a sever effect on the chlorophyll- 
like pigment algorithm. 
INTRODUCTION 
Sunlight incident on the ocean-surface undergoes reflection, refraction, 
Scattering and absorption. The refracted light serves as an ideal tool for 
oceanic studies. As the refracted light penetrates the water body, it undergoes 
multiple scattering and absorption by water molecules and by foreign material 
present in the water. Because of scattering and absorption, the spectral char- 
acteristics of underwater light differ from that of the daylight incident on the 
water surface. It is well known that the underwater spectral characteristics 
are intimately related to the nature of the foreign matter, living or non-living, 
suspended or dissolved, organic or inorganic, present in the water. Thus the 
spectral analysis of the underwater light can provide information about the 
nature and abundance of those materials present in the water which are respons- 
ible for the modification of the spectral characteristics. Alternatively, if the 
presence of a certain material in the water and its effect on the light spectrum 
are known, then one may correlate the underwater spectral signatures with the 
abundance of that particular material. 
Some of the most important materials in ocean water are chlorophylls and 
these pigments have pronounced absorption bands in the blue and red part of the 
visible spectrum. Perhaps Tyler (1) was the first to make use of the optical 
properties of chlorophylls and demonstrated that the scattered underwater light 
seen horizontally can be used to detect phytoplankton if in situ chlorophyll 
concentrations are greater than 1-2 mg/m'. Strickland (2) suggested that it 
might be possible to measure chlorophyll concentrations in water from an aircraft 
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