844 
2 - OPTICAL RESPONSE OF SEA WATER TO LASER EXCITATION 
Because of strong attenuation of light in water, lidar systems are capable for 
effective detecting the backscattered signal emitted from nearsurface water 
column (less than 10 m even in relatively clear waters in the open sea). 
Gating the detecting system synchronously with laser pulse allows to diminish 
the contribution of ambient light to the spectrum. 
In general, there are three important contributions (see Fig.2) to the 
spectrum detected: the water Raman scattering, as well as fluorescence of 
organic matter (both dissolved organic matter (DOM or "yellow substance") and 
oil pollutions) and pigments of phytoplankton (chlorophyll-a (Chl-a) and, for 
some species, phycoerythrin and phycocyanin). Therefore, the lidar technique 
is potentially capable to provide both qualitative and quantitative 
information about important environmental, biological and physical parameters: 
"yellow substance" (Bristow et al., 1985; Reuter et al., 1993; Alberotanza et 
al., 1994, Chekalyuk et al., 1992a) and oil pollutions characteristics (e.g., 
see Hoge and Swift, 1980; Hengstermann and Reuter, 1990), pigment composition 
of phytoplankton (Hoge and Swift, 1981, 1983, 1990; Babichenko, 1994), their 
concentrations and algal photosynthetic activity (e.g. see Chekalyuk and 
Gorbunov, 1992b, 1994), temperature (Leonard et al., 1979; Raimondi and 
Cecchi, 1994) and salinity (Bekkiev et al., 1983) of sea water, light 
attenuation in water column (Bristow et al., 1981, 1985). The combination of 
these capabilities, as well as the capacity for high-resolution day-and-night 
remote monitoring, could provide a wide range of applications of lidar 
techniques for studies of bio-geochemical and physical processes in the sea, 
and for environmental monitoring in coastal zones. 
Figure 1. Block Diagram of Lidar 
System. 
Figure 2. Typical Spectrum of Return 
Signal from Water Excited by Irradi 
ation of Double-Frequency YAG-laser 
(X«x = 532 nm). 
The conventional approach is to normalize the fluorescence contributions 
to water Raman scattering (WRS) to exclude signal affecting by varied 
detecting conditions (Klyshko and Fadeev, 1978; Bristow, 1981; Hoge and Swift, 
1981). The wavelength X R = l/y R of water Raman scattering band is defined by 
the frequency y = 1/X of laser excitation ; y = y — Ay , where Ay = 3440 
_J L L R L R R 
cm . As a result, X = 344 nm in case of UV excitation with XeCl excimer 
R 
laser (X l = 308 nm), and it would be shifted to the red area (X r = 651 nm, see 
Fig.2) with changing the excitation to the second harmonic of Nd:YAG - laser