The light reflected from the sea surface. consists. of sky
radiation and direct solar radiation (sun glitter). The wind-driv-
en waves and Sun^s altitude effect on brightness significantly. If
we have abundant sun glitter in the field of view a bright back-
ground can be observed and its influence on the signal fluctu-
ation is small. Sun glitter prevents the measurements of sea col-
our. Such conditions can be observed as a rule when the Sun”s al-
titude is more than 509 by Eerme, Lokk (1978).
In many cases with the spatial resolution about 30 to 40
meters the reflection from the sea surface (including sun glitter)
produces a steady background and the variability of the signal is
mainly influenced by the sea colour.
From low heights (from aboard the ship) that provides us a
small area for measuring, only separate patches of sun glitter,
having though a considerable influence, can be observed and the
variability of signal fluctuations increases.
Therefore the measurements of single spectra at the. station
give us mainly unreliable data on the sea colour. In our experi-
ments from aboard the ship we use from 50 to 100 spectra measured
in, the. same. point during 50. to. 100 sec. Only. statistical charac-
teristics of these spectra are used (mean values, standard devia-
tion,asymmetry and excess). Analysing the data on surface bright-
ness, we can estimate some of wave characteristics, discover oil
slicks and find dynamical inhomogeneities like velocity gradients,
high turbulence areas etc. (Byalko, Lokk (1981)).
The main information about water is concealed in the sea
colour. It is influenced by optically active matter in the water
as pigments of phytoplankton (mainly chlorophyll), suspended mat-
ter and dissolved organic matter, more precisely, by its opti-
cally active part the so called "yellow substance". In the open
ocean water the correlations between the spectra of upwelling
light and some optically active matter in the water can be found
relatively in ja simple way. looking for chlovophyll, we find it,
in the water combined with yellow substance originated from the
destruction of phytoplankton. But far from the coast the majority
of suspended matter in the water consists of phytoplankton again.
So the absorption inhomogeneities in most spectral areas must have
a good correlation with the quantity of phytoplankton and the
backscattering from suspension due to their algal origin.
The situation in nearshore areas and in closed seas like the
Baltic is different. A lot of yellow substance is carried into the
Sea by rivers from marsh areas. Therefore the correlation between
yellow substance and chlorophyll as a measure of phytoplankton is
poor. Large quantities of suspended matter is picked up from shal-
low areas by waves and mud carried on by rivers.
Trying to gain some insight into the upwelling light spec-
trum, we have to take into account optical properties of all the
optically active substances in the water and to use the whole vis-
ible part of the spectrum for selecting them.
Investigation of water environment on the basis of spectral
curves of brightness or diffuse reflectance of the sea represents
an inverse problem, generally having no unique solution. Therefore,
it is suitable to carrv out numerical experiments calculating the
sets of spectral curves of radiative characteristics for various
concentrations and vertical profiles of optically active matters
in the water. A remarkable contribution to such investigations is
given by the works of Kattawar and Hymphreys (1976), Gordon et al.
(1975, 1980), Plass et al. (1978), Morel and Prieur (1977, 1980),
“aith and Baker (1978, 1980): etc:
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