12. Advances in understanding the mechanisms of fluorescence emission
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Considerable progress is observed in understanding the mechanism of laser induced fluorescence emission. Three
significant advances were presented :
— a new model describing the fluorescence response of algae to pulsed laser excitation, presented by
Gorbunov and Chekalyuk (Russia).
— a comprehensive analysis of blue-green fluorescence of leaves presented by Cerovic et al (LURE, France).
— a time dependent canopy model enabling to separate partly the effects of changes in plant physiology and
canopy geometry by S. Biala (Germany).
2 - APPLICATION DOMAINS
The recent advances provide a solid basis for the development of new approaches based on Ildars for monitoring
crops and forest stresses. The new promising results in this field have been presented in particular by Moya et al.
(France), Colao et al. (Ihdy) and Takahashi et al. (Japan).
Lidar possesses also a great potential in environmental applications. A new method to quantify residue
cover has been reported by Daughtry et al. (USA). Patsayeva (Russia) presented a paper devoted to new
techniques for distinguishing the fluorescent response lirom oil in film (on water surface) and in dispersed form,
as well as from dissolved organic matter.
The review on the state of the art in the field of oceanographic lidar fluorosensors has been presented
by Chekalyuk and Gorbunov (Russia)
3 - FUTURE DEVELOPMENTS :
The laser-induced fluorescence offers new possibilities for monitoring land and sea. Its advantages as compared
to the other systems are :
— capability for real time day and night continuous monitoring (in particular for water pollution);
— space and time scales intermediate between satellite and ground-based measurements;
— high spatial resolution (10 m)
— weak dependence on weather condition;
— recent development of operational system (Germany) to monitor the coastal zones;
However, the main problem to solve is the development of reliable and universal algorithms for data
interpretation.
4 - CONCLUSION
The research activity in the domain of laser-active remote sensing has grown quite fast in the last years. The
mechanism of plant fluorescence are better understood and actually the remote determination of the physiological
status of the plants can rely on three parameters :
— the fluorescence life time
— the fluorescence emission spectrum from blue to red;
— the photo-induced variable fluorescence (pump an probe technique).
In addition, the analysis of the elastically reflected signal enables a fast and accurate description of the
architecture of a plant canopy.
The comprehension of the laser-induced fluorescence mechanisms offers also new perspectives for the
development of passive measurements in the Fraunhofer lines.
