PUMP-AND-PROBE LIDAR TECHNIQUE: NEW APPROACH
TO ACTIVE BIOMONITORING OF SEA AND LAND
A.M. CHEKALYUK and M.Yu. GORBUNOV*
Moscow State University
Dept, of Physics (*Dept. of Chemistry), Moscow 119899 (Russia)
ABSTRACT:
Relying on the relationship between the photosynthesis efficiency and variable
fluorescence of in vivo chlrophyll-a, the lidar implementation of pump-andprobe
pump-andprobe technique can provide a way for remote monitoring of ongoing
photosynthesis in algae and high plants. The basic idea of pump-and-probe
technique is the use of actinic (pump) light flash to cause for a short period
the change in functional state of photosynthetic apparatus. The prototype of
pump-and-probe lidar-fluorosensor is described. The laboratory experiments on
optimalization of laser excitation are discussed. The results of field
measurements in the Mediterranean and Black sea, and in the Atlantic are
presented. This novel lidar technique, capable for remote control over
functional state of the object, may by classified as superactive. The problems
of future development of pump-and-probe lidar technique are discussed.
KEY WORDS: Lidar, Remote Sensing, Photosythesis, Chlorophyll, Fluorescence
1. - INTRODUCTION
Due to recent advances in remote sensing, several promising technologies for
biomonitoring are under development at present time. Nevertheless, there is a
demand for remote technique, capable of providing direct information about
ongoing photosynthesis of algae, plants and terrestrial vegetation. It is
difficult to overestimate the value of such information for global change
studies, monitoring of biological production (including application in
agriculture, forestry and fishery), as well as for environmental survey. Our
recent lidar implementation of pump-and-probe technique may be a step towards
solution of some relevant problems.
2. - RELATIONSHIP BETWEEN IN VIVO CHLOROPHYLL FLUORESCENCE AND
PHOTOSYNTHESIS
Fluorescent methods for estimation of photosynthetic activity of plants and
algae rely on the relationship between fluorescence of chlorophyll-a ( Chl-a)
(the main pigment in photosynthetic apparatus) and the efficiency of photosyn
thesis processes. Below we present a brief summary on biophysical backgrounds
of Chl-a fluorescence emission (see as reviews e.g. Krause and Weis, 1991).
In vivo Chl-a fluorescence accompanies primary stages of photosynthesis,
which include the absorption of photons by pigments of the light-harvesting
antenna, migration of the resulting excitons through the light-harvesting
antenna to the reaction centers (RCs), trapping of excitons by the RCs, and
Primary charge separation (photochemistry). The photochemical energy is used
for fixation and conversion of inorganic C0 2 into sugars and biomass. At room
temperature the major contribution to Chl-a fluorescence is emitted from
photosystem II (PS II) (see e.g. Krause and Weis, 1991).
