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LASER-INDUCED FLUORESCENCE FROM IN VIVO CHLOROPHYLL:
INTERPRETATION ASPECTS IN LIDAR REMOTE SENSING
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M.Yu. GORBUNOV and A.M. CHEKALYUK*
Moscow State University,
Department of Chemistry (*Dept. of Physics), Moscow 119899 (Russia)
i.B. Satterwhite. 1993.
cience Remote Sensing
s by derivative analysis
J.R. Noriega. 1975.
752-755.
il Water Conservation
and reflectance of crop
iasurement techniques.
ABSTRACT:
The present paper is devoted to analysis of some problems related to correct
interpretation of lidar data based on measurements of laser-induced
fluorescence ( LIF) from in vivo chlorophyll-a (Chl-a). The theoretical
description of Chl-a LIF emission caused by nanosecond laser pulses is
presented in the paper. The consequence of practical importance is nonlinear
dependence of Chl-a LIF intensity on power of laser pulses ("saturation of
fluorescence"), manifesting itself even at relatively low levels of excitation
(I > 10 kW/cm -2 ). One of the key problems in data interpretation is high
variability (more than 3-5 times) of in vivo Chl-a fluorescence yield, caused
by changes in physiological state of photosynthetic apparatus due to
environmental influences (light, nutrient availability, etc.). The bright
manifestation of such variations is diurnal rhythm of Chl-a fluorescence yield
of phytoplankton and vegetation caused by changes in solar illumination. The
relevant results of laboratory and field studies are analysed in the paper.
KEY WORDS: Chlorophyll, Fluorescence, Photosynthesis, Lidar, Remote Sensing
1. - INTRODUCTION
Various biological and environmental applications of lidars are based on remo
te detection and spectral analysis of laser-induced fluorescence (LIF) from in
vivo chlorophyll-a (fluorescence emission wavelength is about 685 and 730 nm).
Several lidar techniques are currently developed to provide assessments
of phytoplankton chlorophyll concentration in water (Hoge and Swift, 1981,
1983; Chekalyuk et al., 1992; Chekalyuk and Gorbunov, 1994a,b,c), chlorophyll
content in leaves, physiological status of plants (Chapelle et al., 1984,1991;
Dahn et al, 1992; Edner et al., 1992; Lichtenthaler, 1988,1990; Lichtenthaler
et al., 1992; Zimmermann and Gunther, 1986), and photosynthesis efficiency of
both phytoplankton and vegetation (Chekalyuk and Gorbunov, 1994a,b).
The present paper is devoted to analysis of some problems related to
correct interpretation of lidar data based on Chl-a LIF measurements.
2. - BACKGROUNDS OF LIF FROM CHLOROPHYLL IN VIVO
The problems of interpreting the LIF data originate not from drawbacks of
lidar technique per se, they are determined first of all by the complex nature
°f primary photosynthetic processes accompanied by Chl-a fluorescence
emission. The primary photosynthesis stages include the absorption of photons
by pigments of the light-harvesting antenna, migration of the product excitons
through the light-harvesting antenna to reaction centers (RCs), trapping of
excitons by the RCs, and primary charge separation (see e.g. Krause and Weis,
1991). At room temperature Chl-a fluorescence is emitted predominantly from
Photosystem II ( ps II).
