ts of sky 
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ight back- 
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30 to 40 
sun glitter) 
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vides us a 
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the station 
lr experi- 
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/ gradients, 
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the water 
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find it, 
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ed into the 
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Kf all the 
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of spectral 
represents 
. Therefore, 
lating the 
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e matters 
gations is 
rdon et al. 
77, 1980), 
   
In the present paper the spectral curves (in the range from 
400 to 700 nm) of diffuse reflectance just below the sea surface 
depending on the concentrations and vertical profiles of hydrosols, 
Chlorophyll and yellow substance in the water are computed. The 
total absorption coefficient of the water environment under  con- 
sideration for the wavelength of incident radiation A is  des- 
Cribed by the formula: 
K (A) = Eu (0) + kn (A) Cu + kc(^)& * ky@)Cy , (1) 
where k,"—.spectral absorption coefficient of pure water; KH,kes 
ky - spectral absorption coefficients of hydrosol, chlorophyll and 
yellow substance, correspondingly; cg , Cc , Cy - concentrations 
of the hydrosol, chlorophyll and yellow substance,correspondingly. 
Assuming the light scattering caused by water and hydrosols 
only, the total scattering coefficient may be described: 
DA) = Ou O0) t 6i, (2) 
where ©w and 6,4 - the Spectral scattering coefficients of pure 
water and hydrosol, correspondingly. : 
The numerical values of these spectral absorption and 
scattering coefficients are obtained from the investigation by 
Plass et al. (1978). The mathematical model based on the well-known 
"two-stream approximation" is used (see Arst and Lokk (1981)). The 
Sun”s zenith angle is chosen to be 60° and the corresponding 
values of the relation between the direct and diffuse solar radia- 
tion for clear sky are determined on the basis of the results by 
Avagte et al. (1962). The diffuse reflectance (DR) of the sea’ is 
computed as a relation between the values of upward and downward 
solar irradiance just below the water surface. 
The dependence of /C,| , €c, and €, on the depth (z) in 
the water is assumed to be described by the formula: 
2 -5 
€ - e wxpl- pt -25)*] * exp C (0 z*). : (3) 
Varying the.parameters e , (f and Có one can obtain 
different from each other vertical profiles of c. Fig.l represents 
the profiles of c , corresponding to various numerical values of 
ol + Bp and Y . Besides, the spectra of DR are computed for 
several cH , cce and cy assumed not depending on depth. 
The DR spectral curves are presented both in normalized 
(to A = 520 nm) and unnormalized form. As our estimations show, 
normalized spectra of DR do not depend on the nonselective radia- 
tive characteristics (nearly nonselective are the scattering cha- 
racteristics of seawater). On the contrary, the absolute values of 
the unnormalized DR spectral curves are essentially sensitive to 
the scattering and backscattering coefficients of seawater. Hence, 
if scattering is the main distinguishing feature for decoding, it 
is better to use the absolute spectral values of DR, but if ab- 
sorption is presumably the main distinguishing feature the 
normalized spectral curves must be preferred. However, it must be 
pointed out that in some cases the analyse by collating the 
normalized and unnormalized spectral curves of DR may occur very 
helpful. 
In Fig.2 some results of calculations of the normalized DR 
Spectral curves depending on the concentration of optically active 
substances in the water are shown. Three main cases of the