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Title
Mesures physiques et signatures en télédétection

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 ( ). 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
nondestruc>etween these
of primary
Nevertheless,
mmon problems
difficulties in
î areas,
ir implementa10
implementa10 th photosyn>oard
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.