917 
î-a fluorescence 
;ical state of 
> II RCs. If the 
:e, under weak 
3 a, where P680, 
iate pheophytin 
riding maximum 
As in the case of conventional lidar systems, the pump-and-probe lidar 
provides remote measurements by using laser pulses for excitation of Chl-a 
fluorescence in subsurface water layers. The distinction is that with the 
pump-and-probe lidar this fluorescence is alternately detected in response to 
excitation by the single probe pulses and by the probe pulses following the 
pump pulses. In the first case the actual Chl-a fluorescence intensity (4>) is 
detected, in the second case - the maximum one (<J> ). The function of the 
m 
he influence of 
sfer of RCs to 
The resulting 
ion of variable 
the closed PS 
es between its 
'S II RCs. The 
pumping laser pulse is to cause the transition of previously open RCs to the 
closed state at the moment of probing pulse action; the role of probing pulse 
- to induce Chl-a fluorescence to be detected. 
This novel lidar technique, being capable for remote laser control over 
functional state of photosynthetic apparatus, may be classified as superactive 
(Chekalyuk and Gorbunov, 1993a,b). The basic idea of superactive remote 
sensing is to cause remotely some changes in the object to obtain required 
additional information. 
id Kiefer, 1985) 
is sufficiently 
to the closed 
red in response 
ump flash with 
in response to 
rease in Chl-a 
ence) n = ($ 
m 
this parameter 
its value is a 
conversion in 
Kiefer, 1985). 
iter determines 
>hotochemistry. 
atively simple 
ind irradiance, 
the on-going 
increased the 
ilar - in sea 
l. The use of 
about vertical 
r, nondestruc- 
>etween these 
of primary 
Nevertheless, 
mmon problems 
difficulties in 
î areas, 
ir implementa- 
10 th photosyn- 
>oard a moving 
>rbunov, 1992) 
flashes in the 
.ser pulses, in 
notely. 
4. - PUMP-AND-PROBE LIDAR SYSTEM 
The first prototype of pump-and-probe lidar system has been intended for 
monitoring algal photosynthetic parameters in the sea (Fig.l, left). It 
consists of two pulse YAG:Nd-lasers, the optical system including optical 
multichannel analyzer (OMA) for detection of laser-induced response from water 
column and its spectrum analysis and computer for control of the system and 
data processing. All the components of lidar (excluding folding mirror) are 
mounted inside the laboratory of a research vessel. 
Pulses of the first laser (irradiance wavelength - 532 nm; pulse duration 
- 10 ns; pulse power - 3.5 MW) are utilized as pump ones to close initially 
open RCs PS II. The second laser generates probe pulses (532 nm; 10 ns; 0.5 
MW) to induce Chl-a fluorescence emission. The time delay between pump and 
probe pulses in double-pulse mode is about 30-50 ps. Our estimations and field 
experiments have proved that the described pulses parameters ensure required 
characteristics of irradiance in the subsurface layer of seawater (down to 2-5 
m of depth) if the distance from lidar to water surface is about 10-15 m. 
Figure 1. Block Diagrams of Pump-and-Probe Lidar Systems 
for Phytoplankton (left) and Higher Plants (left) Monitoring.