LASER ACTIVE REMOTE SENSING
A.K. Chekalyuk (1) and G. Guyot (2)
(1) Moscow State University, 119899 Moscow (Russia)
(2) INRA, Bioclimatologie, 84143 Montfavet Cedex (France)
INTRODUCTION
The section was devoted to presentation of recent advances in laser active remote sensing applied to
environmental monitoring. Four papers from France, Russia, Sweden and USA were presented in plenary session
on 20 January and 14 papers (France, Germany, Italy, Japan, Russia, USA) in poster sessions during the
Symposium.
From the last colloquium (Courchevel) a strong evolution can be noted. Three years ago, the research
teams were just starting to consider the blue fluorescence besides the red chlorophyll fluorescence. In Vai d’Isere,
the blue fluorescence was extensively used and analysed, giving complementary information on the physiological
status of the plants. The second evolution is relative to the development of operational field equipment for the
remote determination of plant fluorescence and a prototype was presented by a company in the exhibition
coupled with the symposium.
1 - RECENT ADVANCES
Due to its capability for remote monitoring in vivo plant fluorescence, the lidar technique has a great potential in
the measurement of parameters related to the physiological status of vegetation A number of presented papers
were devoted to recent progress in this promising direction.
1.1. Advances in instrumentation
Three new promising techniques were presented. The two first provide complementary information to the method,
suggested by Lichtenthaler et al., based on the measurement of the ratio of spectral components. The third
concerns fluorescence imaging systems.
Pump and probe lidar technique : developed by Chekalyuk and Gorbunov (Russia) it is based on the
simultaneous use of two lasers : the "pump" gives actinic saturating light pulses changing, for a short time, the
functional state of the photosynthetic apparatus, and the low intensity pulses of the "probe" enables the direct
determination of the ongoing photosynthesis efficiency. This technique has been successfully tested on
phytoplankton and higher plants.
Time resolved fluorescence : the interest of the measurement of the fluorescence life time instead of the
fluorescence intensity, was discussed in the preceding colloquium (Courchevel). But in Val d'Isère the results of
the first measurements performed in field or near-field condition were presented. A prototype of lidar and
interpretation algorithms have been developed in a collaborative efforts of LURE, INRA Bioclimatologie and
CEC JRC (Ispra). In addition the analysis of the time resolved reflected signal, seems to be a promising way for
analysing the threedimentions! structure of a plant canopy, as reported by Camenen et al (INRA, France).
Fluorescence imaging : a new approach in methodology and instrumentation has been implemented by
S van berg et al. (Sweden), Lichtenthaler (Germany) and Miehe (France). The basic idea is the use of fluorescence
imaging system for 2D monitoring of plant leaves. The Swedish equipment is able to acquire remotely
fluorescence images in four spectral bands (blue and red).
Towards passive measurements : The measurement of blue and red fluorescence intensity in the Fraunhofer
lines of the solar spectrum was also proposed and discussed. This approach based on hyper-spectral resolution
measurements could be the starting point of a new way for identifying and monitoring plant canopies.
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