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results and discussion 
The optical properties of the water and reflectance spectra, were 
very different in different seasons for Lake Kinneret. Therefore, 
the results will be presented in the context of apparent Chi 
concentration in the lake: during low Chi period and during the 
Peridinium high Chi period. 
Spectral Features of Reflectance 
Low Chi concentration period . Although we tried to sample as 
wide a range of constituent concentrations as possible, their 
spatial distribution was quite homogeneous. Chi ranged from 3.1 
to 7.3 mg.m 3 in October 1992 and from 5 to 20 mg.m -3 in July 
1993. The acquired reflectance spectra were similar in general 
outline (Fig. la) . A sharp decrease around 440 nm corresponded 
to Chi absorption. The maximum near 560-57 0 nm was caused by 
minimum absorption by all phytoplankton pigments. From 670 to 
675 nm, the lowest levels of reflectance were recorded. The 
minimum was evident for Chi > 4 mg.m -3 , and hardly distinguished 
for Chi < 3.5 mg.m . A small peak around 690 nm, which varied 
from 685 to 695 nm, was recorded in all spectra. This peak 
appeared at 685 nm at the station with maximum water 
transparency; in most spectra the peak was close to 690 nm. At 
wavelengths greater than 690-695 nm the reflectance dropped 
sharply. The spectra converged to a common value at 750 nm. 
Fig. 1: Reflectance spectra recorded in Lake Kinneret (the number 
above the spectrum line indicates the Chi concentration). a) Low 
Chi period; b) High Chi period (Peridinium bloom). 
High Chi concentration period . Representative reflectance 
spectra, acquired in March and April 1993 were pronouncedly 
different (Fig. lb) from the spectra obtained during the low Chi 
period (Fig. la) . For Chi > 30 mg.m a wide minimum from 430 
through 500 nm is seen. In this region of the spectrum, 
reflectance increases with the decrease of Chi concentration. 
This tendency is more pronounced at the domain of 480-520 nm. 
At chl > 2 0 mg.m -3 , the reflectance is extremely low, reaching 
only 1% for the highest values. 
The reflectance peaked between 550 and 58 0 nm. The peak 
width and its magnitude decreased with rise of Chl concentration. 
In samples with highest Chl, it did not exceed 3% due to strong 
absorption by Chl - even at these wavelengths. In the region from 
590 to 650 nm, the reflectance spectra of all the samples with 
Chl > io mg.m 3 were practically uniform.