877 
3 - RESULTS AND DISCUSSION 
3.1. Detection of the water Raman peak 
As anticipated above, illumination of a water column by means of a 308 nm laser radiation gives rise to the 
3300 chi' 1 water Raman shifted signal centered at 344 nm. It has been demonstrated that the peculiar shape of 
the liquid water Raman peak is traceable to the contemporary presence of monomers and molecular aggregates, 
so that it is sensitive to water temperature and salinity, which their mutual equilibrium concentrations [6]. This 
signal is easily detected in the field and on water columns higher than 20 cm, whereas it cannot be used for data 
normalization in the experiments on small photobioreactor (water depth as small as a few cm). 
A part from the water Raman peak, the spectrum of a "clean" water column always contains a 
broad structure due to traces of dissolved impurities. This structure, called Dissolved Organic Material (DOM) 
is peaked around 400 nm and its intensity increases with increasing organic pollution. 
25000 
Fig. 1 - LIF spectra measured upon excitation @ 308 nm on saline solutions containing dif 
ferent algae in a 30 cm high water column. 
3.2 Detection of phytoplankton in water 
This section deals with measurements of phytoplankton dissolved in saline solutions simulating the real brack 
ish water in natural environments, including coastal lakes and open sea. LIF spectra excited on a water column 
by 308 nm radiation, contain the backscattered laser radiation, the water Raman peak and peculiar structures 
extending from the blue to the red spectral region which are related to different phytoplankton pigments [7]. 
Most important phytoplankton fluorescing pigments include carotenoids (emitting between 400 nm and 450 
nm), phycoerithrin (580 nm), pbycocyanin (660 nm), and chlorophylls (685 nm with a shoulder at 730 nm). Ex 
cluding carotenoids emission, which overlaps the DOM emission, all the red pigment fluorescence can be used 
to the remote phytoplankton classification. 
By measuring LIF spectra of phytoplankton, we investigated the feasibility of remotely classify- 
ln 8 its species in major groups, according to their characteristic pigments contents quantified through suitable 
spectral ratios. We considered in the present investigation the Blue-Green (Cyanobacteria) and the Green (Chlo- 
tophyceae) Algae, due to the remarkable importance of these phytoplankton classes, for natural bio-mass pro 
duction in saline waters. A part from small amounts of carotenoids, the Blue-Green Algae contain chlorophylls 
(mostly chlorophyll a) and phycocyanin. In some species, not analyzed here, phycoerithrin is also present The 
Green Algae are basically characterized by chlorophylls (chl-a and chl-b) alone.