POSSIBILITIES FOR REMOTE SENSING OF CHLOROPHYLL 
BY OPTICAL METHODS 
H.ARST, J.LOKK 
Institute of Thermophvsics and Electrophvsics 
Estonian Academy of Sciences 
Paldiski Str.ï. Tallinn 2000371 
Estonian SSR, USSR 
ABSTRACT 
The upwelling light measured above the sea surface provides 
information on the characteristics of the sea: I) the light ref- 
lected from the surface is influenced by the roughness of the sea: 
2) the light backscattered (reflected diffusely) from the water 
depends on the concentrations and types of optically active: subs- 
tances in the sea. In the present paper the possibilities of in- 
terpretation of the light spectra backscattered by seawater are 
considered. 
A calculation model based on the "two-stream approximation" 
is used. The values of diffuse reflectance (DR) just below the 
water surface for I6 wavelengths between 400 X A « 700 nm are 
computed. Three kinds of optically active substances were taken 
into account - suspended matter, yellow substance and chlorophyll. 
DR was calculated for the concentration maxima on depths 2,5,1I0, 
I5 m as well as for homogeneous vertical distribution. The DR 
spectra are presented in normalized and unnormalized form. 
During the last years a lot of experiments have been carri- 
ed out in different countries to study water resources from low 
level carriers as helicopters, planes and ships. These experiments 
are needed for satellite data interpretation to understand the 
processes that effect the light field above the water carrying in 
itself information about water quality, dynamical conditions etc. 
Most of the experiments and theoretical studies are carried out 
for upwelling light proceeding from nadir, because these  condi- 
tions are less complicated for estimations. We have carried ‘out 
our experiments in the open Baltic from R/V "Ayu-Dag" and in 
coastal areas from helicopter and research vessels. 
The main obtained parameters - chlorophyll and suspended 
matter concentrations in the water, Secci disc visibility,salinity, 
temperature, sea state, spectral irradiance were measured in the 
same place simultaneously . On the basis of measurements as 
the first approximation  semiempirical relations have been pre- 
sented by Lokk and Purga (1982). 
The light measured above the sea surface contains double 
information : I) light reflected from the sea surface is influenced 
by the conditions of the sea surface: 2) light diffusely  backscat- 
tered from the water is influenced by the quantity and type of 
optically active matter in the water.