849 
Chl-a concentration reached 8...6 pg/1 and the efficiency of photosynthesis 
was also high (up to 80..90% of reaction centers were active) within the 
patches. On the contrary, Chl-a concentration reduced down to 0.5... 1 pg/1 
accompanying by corresponding reduction of photosynthetic activity (only 
35...50% reaction centers were active) in the areas between patches. 
The profiling lidar measurements were conducted in the framework of joint 
Italian-Russian project "TIRRENO’91" in April, 1991 on board of R/V ’Moskovski 
Universitet’. Along-track profiles of Chl-a concentration (Fig.4) were 
reconstructed on the basis of lidar measurements of Chl-a fluorescence 
adjusted for diurnal variations in Chl-a fluorescence yield. Corrective 
factors were calculated from the measurements of variable Chl-a fluorescence 
with lidar pump-and-probe technique (Chekalyuk and Gorbunov, 1992b, 1994), 
taking into account the current values of solar irradiance. 
The distinctive peculiarity of the Tyrrhenian Sea (as well as the major 
part of the Mediterranean Sea as a whole) is relatively low values of phyto 
plankton biomass, and correspondingly - of Chl-a concentration. With respect 
to lidar biomonitoring, it manifests in the strong requirements imposed upon 
the accuracy of measurements of the spectra and spectral data processing. From 
this point the use of optical multichannel analyzer is of particular impor 
tance. The special software has been developed for quantitative perfect 
calculation of fluorescence parameter 4> (the intensity of fluorescence band 
T normalized to water Raman scattering, see Klyshko and Fadeev, 1978) in this 
particular situation, when the relative intensities of Chl-a fluorescence (in 
the range of water Raman scattering) were as low as 0.01-0.03 in some cases. 
According to monitoring data, the Chl-a concentration varied from 
0.03-0.1 pg/1 in the open part of the Tyrrhenian sea (e.g. the northern part 
of the Chl-a profile presented in Fig.4b) to 0.15-0.3 /jg/1 in more productive 
coastal zones (Fig.4). As a whole, the horizontal distribution of Chl-a 
concentration was quite homogeneous in the open parts of the sea, while we 
observed high spatial variability at both meso- and local scales along the 
coastal zones of South Italy (Fig.4b,c) and Corsica (Fig.4a). 
4.2. Lidar Mapping in the Baltic Sea 
The measurements were conducted in May-June of 1984 (39th cruise of R/V 
’Academic Kurchatov’). More than 50 along-track lidar measurements have been 
performed, the total length of monitoring route was 8390 km. Laser-induced 
fluorescence of in vivo chlorophyll-a (excitation by the second harmonic of 
YAG-laser, X = 532 nm) and organic matter (excitation by nitrogen laser, X = 
337 nm) were detected consequently point-by-point from on board a moving ship. 
Along-track spatial resolution of lidar measurements was about 450 m. 
The maps of horizontal distributions of in vivo Chl-a fluorescence of 
near-surface phytoplankton were reconstructed relying on lidar along-track 
data, adjusted for diurnal variations of Chl-a fluorescence yield. The corres 
ponding maps for 15-30 May and 8-10 June are presented in Fig.5. The situation 
as a whole was determined by development of phytoplankton spring bloom, 
started late in April. The most significant feature of the first distribution 
(Fig.6a) is essential mesoscale patchiness in the central and south parts of 
the explored region. The similar patch structures (e.g. see results of lidar 
mapping in the Antarctic region, Fig.6) of about 10 miles in size are often 
characteristic at the stage of decline of algal bloom. One can see (Fig.5b) 
disappearance of the patches in the central area of the Baltic Sea (the region 
of Gotland hollow) two weeks after the first route measurements in May. 
Fig.7 presents the map of organic matter distribution reconstructed rely 
ing on lidar remote sensing in June of 1984. As in the case of phytoplankton, 
ough there was also essential but more moderate mesoscale variability of horizon 
tal distribution. The comparison between this pattern and that of Fig.6b 
allows to suppose that organic matter patch structures in the south part of 
the area had a natural origin and were in direct connection with phytoplankton