chlorophyll-a absorption feature at 676 nm, R(676). The peak is 
shifting towards longer wavelengths with increasing 
concentration of phytoplankton in the water. We have 
continuous spectra with 2 nm interval. Therefore, the peak value 
was taken from the spectral range 690 nm to 716 nm instead of 
a fixed wavelength like you have to do in the case of satellite 
data. The correlation was very good as seen in Figure 3. The 
Lake Harku samples with chlorophyll-a concentration above 
200 mg/m? make the correlation better than it would have been 
for the lakes with smaller concentrations. The only point 
currently significantly off from the regression line (see Figure 3) 
is Lake Támnaren where the strong winds and shallow water 
depth caused high amount of suspended sediments in the water 
(TSS=64.95). Most of the suspended matter (63%) were organic 
particles absorbing light as the total absorption measured in 
Tamnaren was significantly higher than in most other lakes. 
This may have affected also red part of spectrum used in the 
chlorophyll-a retrieval algorithm. 
  
  
  
250 
mn 200 NS T ut 
t i. 
— 
oo 
E 150 
S 
S 100 
e 
= 
e * 
50 al 2 
= y=111.09x + 17.384 
& s 
°* R? = 0.925 | 
0 0.5 T 1.5 2 2.5 
Maxíred)-R(676) 
Figure 3. Correlation between the height of the reflectance peak 
near 700 nm and concentration of chlorophyll-a. 
Several band-ratio type algorithms were tested for total, organic 
and inorganic suspended matter retrieval (Kallio et al. 2001, 
Doxaran et al. 2005). However, no sufficiently good algorithms 
were found up to now for these lakes. 
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