280 
720- 
March 
A reflectance minimum was found at 670 nm. It was 
approximately 1% and was barely dependent on Chi concentration. 
In samples with Chi concentration < 5 mg.m, a wide shoulder 
was found at 683 nm. This peak was consistently found during the 
low Chi period (Fig. la) . 
The red maximum showed near 700 nm. Its magnitude and 
position were strongly dependent on Chi concentration. The linear 
regression between the log(Chi) and the peak position with r -0.9 
could be summarized as follows (Fig. 2): 
Peak position = 677.1 + 15.5*log(Chi), nm (1) 
Chlorophyll detection 
Low chlorophyll concentration period . The maximum of 
reflectance at 685 nm is caused by Chl-a fluorescence and was 
exploited to estimate Chi concentration in several ways. First, 
the fluorescence line height at 685 nm above the linear 
base line that was drawn between 650 and 715 nm (FLH 650 _ 715 ) was 
measured (Gower, 1980; Doerffer, 1981; Fischer and° Kronfeld, 
1990). The relationship Chi vs. FLH 650-715 gave r 2 = 0.64 and an 
estimation error < 0.71 mg.m -3 : 
Chi = 0.934 + 1.496*10 3 FLH 650 _ 715 , mg.m -3 (2) 
Two alternative algorithms were used to deduce the Chi 
concentration. A linear base line was fixed at 670 and 750 nm 
and FLH at 69 0 nm was measured above the base line. 
It lowered an estimation error to 0.6 mg.m -3 (with r 2 > 0.73): 
Chi = 1.84 + 0.98*10 3 FLH 670 _ 750 , mg.m -3 (3) 
The accuracy of Chi estimation could be further 
improved by determining the sum of reflectance above the 
base line (SUM) in the region from 670 to 750 nm (Fig. 3): 
Chi = 1.8 + 30* SUM, mg.m -3 (4) 
An Chi estimation error < 0.48 mg.m -3 and r 2 > 0.84 were 
achieved.